Imaging of the Mediastinum

Introduction

Mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy

• The middle of the thoracic cavity, located between the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
• Subdivided into the:
  • Superior mediastinum Superior mediastinum Mediastinum and Great Vessels: Anatomy
  • Inferior mediastinum Inferior mediastinum Mediastinum and Great Vessels: Anatomy:
    • Anterior: from the sternum Sternum A long, narrow, and flat bone commonly known as breastbone occurring in the midsection of the anterior thoracic segment or chest region, which stabilizes the rib cage and serves as the point of origin for several muscles that move the arms, head, and neck. Chest Wall: Anatomy anteriorly to the anterior surface of the pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy posteriorly
    • Middle: between the anterior and posterior surfaces of the pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy
    • Posterior: between the posterior surface of the pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy and T4 T4 The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines (diiodotyrosine) in the thyroglobulin. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form triiodothyronine which exerts a broad spectrum of stimulatory effects on cell metabolism. Thyroid Hormones–T12

Imaging modalities

• The common radiologic modalities used to evaluate the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy:
  • Chest X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests
  • CT
  • MRI
• Additional details covering the radiologic modalities for chest evaluation are summarized in Pulmonary Radiology Pulmonary Radiology Pulmonary, or chest, imaging includes imaging of the lungs and surrounding structures in the thorax. Imaging of the chest represents a substantial portion of the imaging tests that are routinely performed. Common imaging methods include X-ray, CT, MRI, and ultrasonography (US). Imaging of the Lungs and Pleura.

Chest Radiograph

Overview

• Chest X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests is the initial modality of choice in evaluating mediastinal structures.
• Positioning:
  • Rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays:
    • There should be no rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays.
    • Spinous processes midway between medial ends of clavicles
  • Visualization:
    • Lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy should be fully visible from apices, above clavicles, to bases Bases Usually a hydroxide of lithium, sodium, potassium, rubidium or cesium, but also the carbonates of these metals, ammonia, and the amines. Acid-Base Balance.
    • Performed in inspiration Inspiration Ventilation: Mechanics of Breathing: 7–10 posterior ribs Ribs A set of twelve curved bones which connect to the vertebral column posteriorly, and terminate anteriorly as costal cartilage. Together, they form a protective cage around the internal thoracic organs. Chest Wall: Anatomy visualized above diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy
    • No superimposition of chin Chin The anatomical frontal portion of the mandible, also known as the mentum, that contains the line of fusion of the two separate halves of the mandible (symphysis menti). This line of fusion divides inferiorly to enclose a triangular area called the mental protuberance. On each side, inferior to the second premolar tooth, is the mental foramen for the passage of blood vessels and a nerve. Melasma over neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess or arms over peripheral chest
• Positioning for specific views:
  • Posteroanterior (PA):
    • The board is against the anterior chest.
    • X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests beams posterior → anterior direction through patient
  • Anteroposterior (AP):
    • The board is against back. 
    • X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests beams anterior → posterior direction through the patient
  • Lateral (from side):
    • The patient is upright.
    • The board is against the side (left or right).
  • Lateral decubitus (from side, lying down):
    • The patient is supine.
    • The board is against the side.
    • Usually left side down on table

PA view

• The trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy is midline. 
• The shadow of the superior vena cava Superior vena cava The venous trunk which returns blood from the head, neck, upper extremities and chest. Mediastinum and Great Vessels: Anatomy (SVC) is immediately to the right of the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy. 
• The right and left hila are seen. 
• The right (right atrium) and left (left ventricle) heart borders are clearly visible. 
• Portions of ascending and descending aorta Descending aorta Mediastinum and Great Vessels: Anatomy are visible.

Lateral view

• The retrosternal space is clear.
• The anterior (right ventricle) and posterior (right atrium) heart borders are visible.
• The right hemidiaphragm is slightly higher.
• The hila overlap each other in this view.

Compartments of the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy

• Anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy (prevascular):
  • Area between the sternum Sternum A long, narrow, and flat bone commonly known as breastbone occurring in the midsection of the anterior thoracic segment or chest region, which stabilizes the rib cage and serves as the point of origin for several muscles that move the arms, head, and neck. Chest Wall: Anatomy to the anterior heart border (essentially anterior to the pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy) 
  • Contents:
    • Thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System: Anatomy
    • Fat
    • Lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy
    • Internal mammary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
  • In adults, most common area of mediastinal masses
  • Mediastinal masses typically found here (“Terrible Ts”):
    • Thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs
    • Teratoma/germ cell tumor Tumor Inflammation (GCT)
    • (Terrible) lymphoma
    • Thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy tissue
• Middle mediastinum Middle mediastinum Mediastinum and Great Vessels: Anatomy (visceral):
  • Area extending from the anterior to posterior margins of the heart 
  • Lies between the anterior and posterior mediastinum Posterior mediastinum Mediastinum and Great Vessels: Anatomy
  • Contents:
    • Pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy
    • Heart
    • Aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy and its branches
    • Vena cava
    • Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy
    • Esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy
  • Masses typically found:
    • Lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy (LAD)
    • Cystic Cystic Fibrocystic Change masses
    • Vascular aneurysms
    • Esophageal tumors
• Posterior mediastinum Posterior mediastinum Mediastinum and Great Vessels: Anatomy (paravertebral):
  • Area extending from the posterior wall of the pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy to the spinous processes (includes the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy)
  • Contents:
    • Spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy (SC)
    • Thoracic spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy
    • Neurovascular bundle
    • Sympathetic chain
  • Masses typically found here:
    • Neurogenic tumors
    • Thoracic spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy lesions
    • Meningocele Meningocele A congenital or acquired protrusion of the meninges, unaccompanied by neural tissue, through a bony defect in the skull or vertebral column. Neural Tube Defects 
    • Extramedullary hematopoiesis Extramedullary Hematopoiesis Primary Myelofibrosis (can present as a soft-tissue mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast)

Computed Tomography

Overview

• CT identifies the location of the pathology accurately and is thus the modality of choice in evaluating the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy.
  • Contrast helps define structures (e.g., vasculature, lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy, mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast).
  • The degree and variability of attenuation of a mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast or structure depends on its content.
  • Hounsfield units Hounsfield Units Computed Tomography (CT) ( HUs HUS Hemolytic uremic syndrome (HUS) is a clinical phenomenon most commonly seen in children that consists of a classic triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Hemolytic uremic syndrome is a major cause of acute kidney injury in children and is most commonly associated with a prodrome of diarrheal illness caused by shiga-like toxin-producing bacteria. Hemolytic Uremic Syndrome) measure the density of the structures:
    • Air (seen in pneumomediastinum Pneumomediastinum Mediastinitis): lowest HU HU Computed Tomography (CT)
    • Fat
    • Water
    • Soft tissue Soft Tissue Soft Tissue Abscess
    • Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)/calcification
    • Bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types: highest HU HU Computed Tomography (CT)
  • Window levels: digital manipulation of the images to accentuate structures (e.g., in soft-tissue window, soft tissues such as muscles are seen well)

Normal findings

• The trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy is visible as a black air-filled space.
• Heart:
  • 4 chambers are visible. 
  • The pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy (made of 2 layers) is seen as a linear line (upper limit Limit A value (e.g., pressure or time) that should not be exceeded and which is specified by the operator to protect the lung Invasive Mechanical Ventilation is 2 mm thick) enclosing the heart and great vessels.
• Blood vessels:
  • Blood-filled structures appear brighter in CT with contrast CT with Contrast Imaging of the Head and Brain.
  • Major vessels (pulmonary arteries and veins Arteries And Veins ACES and RUSH: Resuscitation Ultrasound Protocols, aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy, and SVC) are continuous with the heart.
  • Each smaller (black) bronchus is paired with a blood vessel (white).
• Bony structures: ribs Ribs A set of twelve curved bones which connect to the vertebral column posteriorly, and terminate anteriorly as costal cartilage. Together, they form a protective cage around the internal thoracic organs. Chest Wall: Anatomy, vertebrae, scapulae, and humeri should be visible and lightest in color (the most dense structures).

Magnetic resonance imaging

Overview

MRI

• Usually used to study mediastinal masses, specifically to:
  • Determine precise location
  • Assess invasion and staging Staging Methods which attempt to express in replicable terms the extent of the neoplasm in the patient. Grading, Staging, and Metastasis (subcarinal and aorticopulmonary lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs node masses are well visualized in coronal Coronal Computed Tomography (CT) and sagittal Sagittal Computed Tomography (CT) sections)
  • Evaluate for mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast contents (due to excellent resolution of soft-tissue structures)
• Also indicated for those with contrast allergy Allergy An abnormal adaptive immune response that may or may not involve antigen-specific IgE Type I Hypersensitivity Reaction and/or renal failure Renal failure Conditions in which the kidneys perform below the normal level in the ability to remove wastes, concentrate urine, and maintain electrolyte balance; blood pressure; and calcium metabolism. Renal insufficiency can be classified by the degree of kidney damage (as measured by the level of proteinuria) and reduction in glomerular filtration rate. Crush Syndrome
• Not associated with ionizing radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma
• Among the disadvantages:
  • High cost 
  • Longer scan time

Normal Findings

• Views:
  • T1-weighted image (T1):
    • Tissues with high fat content appear bright/white.
    • Compartments filled with water appear dark/black.
  • T2-weighted image (T2):
    • Compartments filled with water appear bright/white.
    • Tissues with high fat content appear dark/black.
• Structures:
  • Thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System: Anatomy:
    • Soft-tissue lobulation
    • Convex, straight, or concave edges based on patient age 
    • Largest ages 12–19, then involutes (7 mm after age 19)
  • MRI demonstrates heart:
    • Muscle thickness
    • Ventricular size
    • End diastolic volume
  • Soft-tissue structures:
    • SC
    • Pulmonary parenchyma
    • Diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy
    • Top of liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
    • Vasculature

Abnormal Findings

Overview

• Abnormalities include:
  • Pneumomediastinum Pneumomediastinum Mediastinitis
  • Vascular abnormalities
  • Masses (e.g., tumors, cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change)
• These conditions can produce widened mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy, but there are normal variants to consider that can also produce the same effect:
  • AP projection (instead of PA projection)
  • Mediastinal fat (in the obese or those on steroid therapy)
  • Vascular tortuosity (noted in the elderly)
  • Low inspiratory supine position

Pneumomediastinum Pneumomediastinum Mediastinitis

• Extraluminal gas (which may be from the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy, trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy, esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus: Anatomy, peritoneal cavity Peritoneal Cavity The space enclosed by the peritoneum. It is divided into two portions, the greater sac and the lesser sac or omental bursa, which lies behind the stomach. The two sacs are connected by the foramen of winslow, or epiploic foramen. Peritoneum: Anatomy) found in the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy 
• Radiographic findings:
  • Linear lucencies outlining mediastinal structures:
    • Bronchi Bronchi The larger air passages of the lungs arising from the terminal bifurcation of the trachea. They include the largest two primary bronchi which branch out into secondary bronchi, and tertiary bronchi which extend into bronchioles and pulmonary alveoli. Bronchial Tree: Anatomy or trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy
    • Major blood vessels
    • Pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy and heart
  • Findings are consistent with air surrounding the structure(s):
    • Thymic sail sign Sail Sign Supracondylar Fracture: upward shift of thymic lobes, forming a triangular inferior thymic border (found in neonates)
    • “Ring around the artery” sign: gas around major aortic branches
    • Double bronchial wall sign: gas surrounding the bronchial wall
    • Continuous diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy sign: air between the diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy and the pericardium Pericardium A conical fibroserous sac surrounding the heart and the roots of the great vessels (aorta; venae cavae; pulmonary artery). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers. Heart: Anatomy
  • SC emphysema Emphysema Enlargement of air spaces distal to the terminal bronchioles where gas-exchange normally takes place. This is usually due to destruction of the alveolar wall. Pulmonary emphysema can be classified by the location and distribution of the lesions. Chronic Obstructive Pulmonary Disease (COPD) is also seen.
• CT findings:
  • Provides more details regarding coexisting illness or injuries (involving the aerodigestive tract)
  • Also detects small air accumulations not seen on chest radiograph

Thyroid-related masses

• Can be:
  • An enlarged thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy gland ( goiter Goiter A goiter is a chronic enlargement of the thyroid gland due to nonneoplastic growth occurring in the setting of hypothyroidism, hyperthyroidism, or euthyroidism. Morphologically, thyroid enlargement can be diffuse (smooth consistency) or nodular (uninodular or multinodular). Goiter) or thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast ( benign Benign Fibroadenoma nodule Nodule Chalazion or malignant tumor Tumor Inflammation) extending (from the neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess) into the intrathoracic area
  • An ectopic thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy
• The majority of goiters found in the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy are anterior to the brachiocephalic vessels.
• Radiographic findings:
  • Opacification in the anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy
  • Widened mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy
  • +/- Mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast effect: tracheal deviation Tracheal Deviation Pneumothorax to the opposite side
• CT findings:
  • Anterior mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
  • Goiters:
    • Heterogeneous density
    • Marked contrast enhancement
  • Thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy nodules:
    • Common incidental findings on CT
    • American College of Radiology suggests follow-up ultrasound for incidental nodules: if > 1 cm in those aged < 35 years, or > 1.5 cm in those aged > 35 years
    • Features suggestive of malignancy Malignancy Hemothorax: ill-defined or irregular margins, tissue invasion, and/or LAD

Teratoma

• GCT that typically presents as a large mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
• 20% are malignant.
• The anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy is the most common extragonadal site.
• Variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables contents:
  • Fat or fat-fluid levels
  • Cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change
  • Calcification
  • Soft tissue Soft Tissue Soft Tissue Abscess
• Radiographic findings:
  • Opacification in the anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy
  • Widened mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy
  • +/- Mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast effect (e.g., tracheal deviation Tracheal Deviation Pneumothorax to the opposite side)
  • +/- Calcification and/or fat
  • In some, teeth Teeth Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are composed of enamel, dentin, and dental cement. Teeth: Anatomy or bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types is seen.
• CT findings:
  • CT scan is the radiologic exam of choice.
  • Anterior mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast with mixed density components related to the multiplicity of contents
  • Fat-fluid level in the mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast: pathognomonic
  • +/- Mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast effect
  • Benign Benign Fibroadenoma (mature) teratomas Teratomas A true neoplasm composed of a number of different types of tissue, none of which is native to the area in which it occurs. It is composed of tissues that are derived from three germinal layers, the endoderm, mesoderm, and ectoderm. They are classified histologically as mature (benign) or immature (malignant). Ovarian Cancer are well defined.
  • Features of malignancy Malignancy Hemothorax:
    • Ill defined 
    • Invasion
• MRI findings:
  • Anterior mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
  • Fat-fluid level is diagnostic.
    • MRI detects macroscopic fat (like CT) but also determines microscopic intracellular fat (not detected by CT).
    • T1-/T2-hyperintensity and saturation on fat-saturated MRI pulse sequences Pulse Sequences Magnetic Resonance Imaging (MRI) confirm macroscopic fat.
  • Calcification can be:
    • Rim-like 
    • Focal 
  • +/- Mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast effect
  • +/- Septation

Thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs and thymic carcinoma

• Tumors:
  • Thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs:
    • Most common primary tumor Tumor Inflammation in the anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy 
    • 20% of mediastinal tumors
  • Thymic carcinomas: aggressive malignancy Malignancy Hemothorax, often presenting with invasion of structures in the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy
• Radiographic findings:
  • Well-defined anterior mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast, seen as a lobulated soft-tissue density 
  • Typically slightly more protruding on 1 side
  • Lateral view: The retrosternal space is opacified.
  • +/- Calcification
• CT findings: 
  • Thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs:
    • Sharply demarcated, encapsulated Encapsulated Klebsiella mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
    • Often with smooth contour
    • Round- or oval-shaped
    • Enhances with contrast
    • Often homogeneous Homogeneous Imaging of the Spleen but can have focal areas of hemorrhage, necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage, or cyst formation
    •  +/- Calcification 
  • Thymic carcinoma:
    • Anterior mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast 
    • Irregular borders
    • Often heterogenous, with necrotic, cystic Cystic Fibrocystic Change, or hemorrhagic components
    • Heterogeneous enhancement Heterogeneous Enhancement Imaging of the Spleen
    • +/- Calcifications
    • +/- Local invasion or LAD
    • +/- Extrathoracic metastases
• MRI findings:
  • Thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs:
    • Well-defined mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast in the anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy 
    • Oval-/round-shaped
    • Usually homogeneous Homogeneous Imaging of the Spleen 
    • Isointense to slightly hyperintense Hyperintense Magnetic Resonance Imaging (MRI) to muscle on T1 images
    • Typically slightly hyperintense Hyperintense Magnetic Resonance Imaging (MRI) to muscle on T2 images 
  • Thymic carcinoma:
    • Anterior mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
    • Irregular borders
    • Hypo- to isointense on T1-weighted images T1-Weighted Images Imaging of the Head and Brain
    • Hyperintense Hyperintense Magnetic Resonance Imaging (MRI) on T2-weighted images T2-Weighted Images Imaging of the Head and Brain
    • Heterogenous
    • +/- Local invasion or LAD

Lymphoma

• Types commonly found in the mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy:
  • Nodular sclerosing Hodgkin lymphoma Hodgkin lymphoma Hodgkin lymphoma (HL) is a malignancy of B lymphocytes originating in the lymph nodes. The pathognomonic histologic finding of HL is a Hodgkin/Reed-Sternberg (HRS) cell (giant multinucleated B cells with eosinophilic inclusions). The disease presents most commonly with lymphadenopathy, night sweats, weight loss, fever, splenomegaly and hepatomegaly. Hodgkin Lymphoma (NSHL)
  • Primary mediastinal B cell lymphoma
• Radiographic findings:
  • Anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy location
  • Widened mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy
  • Retrosternal space obscured
• CT findings:
  • Anterior mediastinum Anterior mediastinum Mediastinum and Great Vessels: Anatomy (although can be seen in the other mediastinal compartments)
  • Irregular contours (often with areas of conglomeration appearing as a large mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast)
  • Homogeneous Homogeneous Imaging of the Spleen, with soft-tissue attenuation (but can be heterogeneous if with necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage or hemorrhage)
  • Mild-to-moderate enhancement 
• MRI findings: vary with the type of lymphoma

Bronchogenic cyst

• Anomalous congenital Congenital Chorioretinitis outpouching of the foregut Foregut Development of the Abdominal Organs
• The middle mediastinum Middle mediastinum Mediastinum and Great Vessels: Anatomy is the most common location.
• Radiographic findings:
  • Soft-tissue density, round or ovoid mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast(es)
  • +/- Air-fluid level
  • +/- Calcification
• CT findings:
  • Well-defined oval-/round-shaped mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast(es) 
  • Smooth borders
  • Varying attenuation due to different contents
  • Homogeneous Homogeneous Imaging of the Spleen
  • No enhancement
  • No invasion
• MRI findings:
  • Rarely needed for evaluation
  • Homogeneous Homogeneous Imaging of the Spleen 
  • Variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables T1, dependent on cyst contents (low intensity in fluid, high intensity in protein content)
  • Hyperintense Hyperintense Magnetic Resonance Imaging (MRI) on T2
  • No enhancement
  • No invasion

LAD

• LAD is the most common mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast in the middle mediastinum Middle mediastinum Mediastinum and Great Vessels: Anatomy.
• Middle mediastinal lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy:
  • Paratracheal
  • Subcarinal: below the tracheal bifurcation
  • Subaortic
  • Tracheobronchial (pulmonary root, hilar)
• Causes include lymphoma, lung cancer Lung cancer Lung cancer is the malignant transformation of lung tissue and the leading cause of cancer-related deaths. The majority of cases are associated with long-term smoking. The disease is generally classified histologically as either small cell lung cancer or non-small cell lung cancer. Symptoms include cough, dyspnea, weight loss, and chest discomfort. Lung Cancer, and sarcoidosis Sarcoidosis Sarcoidosis is a multisystem inflammatory disease that causes noncaseating granulomas. The exact etiology is unknown. Sarcoidosis usually affects the lungs and thoracic lymph nodes, but it can also affect almost every system in the body, including the skin, heart, and eyes, most commonly. Sarcoidosis.
• Radiographic findings:
  • Middle mediastinal mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast(es)
  • Smooth borders
  • May be bilateral
  • +/- Splaying of the carina in subcarinal LAD
• CT findings: The abnormal lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs node has a short-axis diameter >1 cm.

Aortic aneurysm Aortic aneurysm An abnormal balloon- or sac-like dilatation in the wall of aorta. Thoracic Aortic Aneurysms

• A thoracic aortic aneurysm Aortic aneurysm An abnormal balloon- or sac-like dilatation in the wall of aorta. Thoracic Aortic Aneurysms is the abnormal dilation of a segment of the thoracic aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy with the majority affecting the ascending aorta Ascending aorta Mediastinum and Great Vessels: Anatomy.
• Radiographic findings:
  • Widened mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels: Anatomy 
  • Smooth borders
  • Large aortic knob
  • +/- Calcifications
  • Deviation or compression Compression Blunt Chest Trauma of trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea: Anatomy or left mainstem bronchus
  • Note: cannot distinguish a thoracic aortic aneurysm Aortic aneurysm An abnormal balloon- or sac-like dilatation in the wall of aorta. Thoracic Aortic Aneurysms from a tortuous aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy
• CT findings:
  • CTA CTA A non-invasive method that uses a ct scanner for capturing images of blood vessels and tissues. A contrast material is injected, which helps produce detailed images that aid in diagnosing vascular diseases. Pulmonary Function Tests is the best modality ( MRA MRA Imaging of the Heart and Great Vessels is an option but is not readily available in many centers).
  • Detects aortic diameter, vessel anatomy, dissection, rupture, thrombus
  • Shows a dilated aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy
  • +/- Filling defect (representing a thrombus or dissection)

Schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma

• Most common neurogenic mediastinal tumor Tumor Inflammation
• Often arising posteriorly, in the neural foramina
• CT findings:
  • Located in the posterior mediastinum Posterior mediastinum Mediastinum and Great Vessels: Anatomy 
  • “Dumbbell” configuration (demonstrating the tumor Tumor Inflammation being “squeezed” through a neural foramen)
  • Heterogeneous
    • Cystic Cystic Fibrocystic Change changes
    • Hemorrhage
  • +/- Calcifications 
  • Enhances with contrast
• MRI findings: hyperintensity on T2