Radiologic anatomy

Cross-sectional imaging is increasingly replacing fluoroscopic techniques for imaging the small bowel, but both still have a role. It is crucial to recognise the normal appearances of the bowel on all imaging modalities to diagnose abnormality and recognise normal variants. This talk will review the embryological development of the small bowel of importance to radiologists. The aetiology of common congenital malformations such as malrotations and Meckel’s diverticulum will be outlined. The appearance of the normal small bowel on the various imaging modalities will be reviewed, along with pitfalls in interpterion.

Peritoneal anatomy plays a key role in the dissemination process of intraabdominal inflammatory fluid collections or malignant diseases. The peritoneum, a serous membrane, is reflected over abdominal organs to form a series of folds known as ligaments, mesenteries and omenta. They may act as conduits or barriers in the spread of intra- or extra-peritoneal diseases and they influence the peritoneal fluid circulation- responsible for malignant intraperitoneal seeding - along with bowel peristalsis, gravity and hydrostatic pressure gradients. Although not directly visible on imaging, the twelve major peritoneal ligaments and mesenteries can be identified by their typical position, organ relationships, fatty composition and anatomic landmarks provided by their constituent vessels. Peritoneal folds involved by oedema, inflammation or neoplastic infiltration alter their composition, become thickened, and they are directly recognised on imaging. Multiplanar CT reconstructions and specific MRI sequences are useful in demonstrating ligaments and mesenteries. Peritoneal reflections subdivide the peritoneal cavity into multiple compartments and recesses that are visualised when distended by the fluid. These subdivisions provide the anatomic basis for localisation of ascites, abscesses, seeded metastases and traumatic effusions. Familiarity with the normal anatomy is essential in the clinical radiologic analysis and differential diagnosis of peritoneal and mesenteric pathology.

A knowledge of neck spaces not only allows for better communication between radiologists and specialists familiar with imaging of this region but also aid in diagnosis as each space has a distinct group of pathologies. It considerably narrows down the differential diagnosis. The anatomy of the neck can be divided into suprahyoid and infrahyoid portions: suprahyoid neck which encompasses the deep spaces between skull base and hyoid bone and infrahyoid neck which lies inferiorly between the hyoid bone and both clavicles. These divisions are arbitrary in there is some continuation of suprahyoid neck spaces into the infrahyoid neck spaces and continuation of some infrahyoid neck spaces into the superior mediastinum.

The anatomy of the external auditory canal, middle ear and bony inner ear is best studied with CT. The highest resolution can be achieved when ConeBeam CT is used, and this technique also has the advantage that there is no quality loss in the axial, coronal and double oblique plane, the planes needed to study the temporal bone anatomy in detail. Double oblique images are indispensable to visualise the stapes, stapes footplate and oval window. Anatomical knowledge is especially needed at those sites where pathology most frequently occurs and changes the anatomy. The footplate, stapes, lenticular and lengthy process of the incus, facial nerve canal, Jacobson’s canal, the scutum, round window, ligaments etc. are some of these structures and they should be studied in detail in every single patient. MR is better suited to demonstrated the anatomy of the membranous labyrinth, inner ear fluid spaces and nerves in the internal auditory canal. Heavily T2-weighted images are best suited to see these structures, but high resolution is needed. Not only the fluid inside the labyrinth must be evaluated but also the normal size of the different nerve branches in the internal auditory canal must be known in order to be able to detect nerve atrophy or hypoplasia. The most important anatomical structures of the temporal bone, as they can be visualised in different planes on (CB)CT and MR will be illustrated in this presentation.

The larynx is a specialised organ placed at the separation between the respiratory and the digestive tracts. Beyond protecting the airways against food aspiration, it is involved in breathing, swallowing and voiced sounds production. These functions are mostly accomplished by the action of three diaphragms: the epiglottis, the false and vocal cords. All of them, when closed, contribute to seal the larynx during swallowing. When opened, they permit the passage of the air into the trachea. The vibration of the vocal cords (the most caudal of the three sphincters) generates voiced sounds. The vibration is produced by the coordinated action of a group of laryngeal muscles. These muscles are inserted on rigid structures, provided in the larynx by a framework of ossified cartilages: cricoid, thyroid and arytenoid. Cricoid and thyroid cartilage form also a rigid box, a sort of shield. Muscle contraction results in a significant shortening and change of shape. To accommodate these changes, a malleable material (fat) fills the "gap" between muscles and the rigid shield. The lateral "fat-filled-gap" between muscles involved in vocal cord vibration and the cartilage framework is named paralaryngeal space. A midline "fat-filled-gap" separates the epiglottis from the rigid thyroid laminae. CT and MR may precisely delineate the submucosal structures: muscles, fat-filled-gaps (paralaryngeal and pre-epiglottic spaces) and depict un-ossified and ossified cartilages.

Bony landmarks at the lateral epicondyle include the tubercles, intertubercular sulcus, supracondylar ridge, and epicondylar ridge. Tendons include the brachioradialis, ECRL, ECRB, EDC, EDM, ECU and anconeus. Ligaments include the radial collateral ligament, annular ligament and LUCL. Pathological conditions include ligament tears, tendinosis, tendon tears and posterolateral instability. Bony landmarks at the medial epicondyle include the tubercles, intertubercular sulcus, epicondylar face and supracondylar ridge. Tendons include the pronator teres, FCR, Palmaris longus, FCU, FDS. Ligaments include the different components of the UCL. Pathological conditions include ligament tears, tendinosis, tendon tears, and VEO. Understanding bony landmarks at the epicondyles help understand tendon and ligament changes. Pathological conditions are then more easily assessed including tendinosis, tendon tears, ligament tears, VEO and posterolateral instability.

The biceps brachii muscle consists of two heads, the short head and the long head. The two muscle bellies can have some degree of interdigitation proximal to the distal tendon, but they have two separate tendons, one for each muscle at the radial tuberosity insertion. The tendon of the short head attaches distally and slightly anteriorly at the radial tuberosity, whereas the tendon of the long head attaches more proximally. Distal biceps insertion is reinforced by a thin fibrous structure called lacertus fibrosus. Common lesions of the biceps tendons at the elbow include complete ruptures with retraction of the muscle belly or partial tears with different imaging appearance. Partial tears can involve the short or the long head of the biceps brachii tendon. Imaging can shift the therapeutic management from surgical to conservative especially in patients with partial tears. Other disorders related to the distal biceps brachii muscle include impingement and bicipito-radial bursitis. Brachialis muscles injuries are extremely rare. Triceps tendon ruptures can be acute traumatic or more commonly chronic overuse causing degenerative changes to the insertion. Rupture of the distal triceps tendon is uncommon and it may be unrecognised on clinical examination. The most common disruption is an avulsion from the osseous tendon insertion. MRI and US are useful in preoperative planning because it shows whether the rupture is complete or partial. Sometimes, triceps muscle may be a factor contributing to ulnar nerve luxation at the elbow.

Synovial plicae are folds of synovial tissue, remnants of embryonic septae of the normal articular development. Plicae have not well-known function and are usually asymptomatic. Chronic inflammation secondary to direct trauma, repetitive sports activities or surgical procedures of the elbow affects the elasticity of the synovial folds and can become symptomatic, sometimes termed elbow synovial fold syndrome, or posterolateral impingement. With elbow motion, the thickened fibrotic plicae can irritate the synovium, leading to inflammatory synovitis and radial head or capitulum articular cartilage wear. The painful snapping of the elbow joint is the most common clinical manifestation. This condition is not uncommon and commonly misdiagnosed as lateral epicondylitis. MRI and CT or MR arthrography are useful tools in the diagnosis of elbow synovial fold syndrome and for exclusion other causes of lateral elbow pain and snapping. Cartilage injuries usually affect the weight-bearing joints, such as the hip and knee and the elbow is one of the least affected joints. Chondral injuries of the elbow usually occur secondary to a previous injury such as elbow dislocation, fractures or chronic mechanical overload in manual workers, throwing sports or people using crutches and wheelchairs. Morphological MRI allows a precise assessment of macroscopic lesions of the articular cartilage. Furthermore, advanced MRI techniques also enable evaluation of the biochemical or ultrastructural composition of articular cartilage and detect early chondral damage.

Several pathological conditions can arise from such a complex anatomical structure as the mediastinum, including large airways, large and small vessels, lymph nodes, adipose tissue, nerves, oesophagus, heart, and pericardium. The wide spectrum of mediastinal diseases makes their differential diagnosis very challenging at times. To simplify the clinical approach to the mediastinal lesions many classifications of the mediastinum based either on either chest radiography or CT have been proposed. Knowledge of the most appropriate technique to use in each clinical context as well as knowledge of specific imaging signs and features are needed to narrow the spectrum of differential diagnosis and to address most questions arisen when a mediastinal mass is either seen or suspected at chest radiography. Old and new classifications will be compared and their value discussed as well as signs useful in localising and characterising mediastinal lesions will be examined.

Present lecture aims to review the normal anatomy of chest vasculature including caval venous system, great vessels and coronary arteries. Common and less common variants and anomalies will also be displayed and classified, analysing strength and weakness of different imaging methods. Some of these anomalies are found in children having impact, but they are more commonly discovered later in adulthood. Many of these anomalies are asymptomatic or 'leave alone' lesions, but some of these anomalies are symptomatic and need to be treated. Not only cardiovascular imaging dedicated physicians but all general radiologist we have to be familiar with normal vascular anatomy as well as common and less common anomalies.