Saber-sheath trachea refers to diffuse coronal narrowing of the intrathoracic portion of the trachea with the concomitant widening of the sagittal diameter. It is not uncommon and is pathognomonic for chronic obstructive pulmonary disease (COPD) 1.
The sagittal:coronal diameter is over 2:1 2 a...
The saber sign refers to a pattern of gas distribution seen in supine radiographs of patients with pneumobilia. A sword-shaped lucency is apparent in the right paraspinal region of the upper abdomen representing arching gas extending from the common bile duct into the left hepatic duct. This i...
Saccular cerebral aneurysms, also known as berry aneurysms, are intracranial aneurysms with a characteristic rounded shape and account for the vast majority of intracranial aneurysms. They are also the most common cause of non-traumatic subarachnoid haemorrhage.
When larger than 25...
Sacral agenesis (also considered as part of the caudal regression syndrome) is a rare and severe sacral developmental abnormality.
In normal pregnancy, the incidence is between 0.005 and 0.1%. However, in fetuses with diabetic mothers, the incidence rises to 0.2%. Of those with th...
Sacral dimples are a clinical and radiological feature that is associated with occult spinal dysraphism (e.g. tethered cord syndrome) but are more frequently a non-significant isolated finding.
Common in healthy children (~5%) 1.
Simple sacral dimples have the followin...
The sacral hiatus corresponds to the posterior caudal opening at the end of the sacral canal, which usually occurs at the fifth sacral vertebra (S5), at the posterior surface of the sacrum.
Commonly, the sacral hiatus corresponds to the non-formation of S5 spinous proce...
Sacral insufficiency fractures are stress fractures, which are the result of normal stresses on abnormal bone, most frequently seen in the setting of osteoporosis. They fall under the broader group of pelvic insufficiency fractures.
They are usually seen in elderly female...
A very wide range of lesions can occur in and around the sacrum.
primary sacral tumours
sacral chordoma: most common primary sacral tumour 1
Ewing sarcoma /pPNET
osteosarcoma: often arises from Paget's disease in this location
A mnemonic to remember anterior components of sacral plexus include:
Too much sex in the quad
tibial portion (L4-S2) of the sciatic nerve (L4-S3)
nerve to internal obturator and superior gemellus muscles (L5-S2)
nerve to quadratus femoris and inferior gemellus muscles (L4-S1)
A mnemonic to remember posterior components of sacral plexus include:
Clean Guys Floss
C: common peroneal nerve
G: gluteal (superior and inferior) nerves
F: femoral cutaneous (posterior) nerve
The sacral plexus is formed by anterior rami of L4 to S5 and its branches innervate the pelvis, perineum and lower limb.
The sacral plexus forms on the anterior belly of the piriformis muscle and is formed by the lumbosacral trunk (L4-5) of the lumbar plexus, which enters the pel...
A handy mnemonic to recall the branches of the sacral plexus prior to its division is:
Six Ps - As all of the nerves start with the letter P.
SLIP, DSP - if you slip over, you may need to go on the DSP (Disability Support Pension).
nerve to piriformis (S1-S2)
Sacro-coccygeal teratoma (SCT) refers to a teratoma arising in the sacro-coccygeal region. The coccyx is almost always involved 6.
Demographics and clinical presentation
It is the commonest congenital tumour in the fetus 11 and neonate 3. The incidence is estimated at ~1:35000-40000. There is ...
The sacroiliac (SI) joint is a synovial and fibrous joint between ilium and the sacrum. It has little movement and its main function is to transfer weight between the axial and lower appendicular skeletons. The SI joint is a symmetrical joint (i.e. is paired) with an oblique coronal orientation ...
Sacroiliitis (inflammation of the sacroiliac joints) can be a manifestation of a wide range of disease processes. The pattern of involvement is helpful.
Usually bilateral and symmetrical
inflammatory bowel disease
Sacroiliac joint injections can be performed using a posterior approach into the the sacroiliac joint under fluoroscopic or CT guidance.
Sacroiliitis grading can be achieved using plain radiographs according to the New York criteria 4.
grade 0: normal
grade I: some blurring of the joint margins - suspicious
grade II: minimal sclerosis with some erosion
definite sclerosis on both sides of joint 5
severe erosions wi...
The sacrospinous ligament is a stabiliser of the sacro-iliac joint and connects the bony pelvis to the vertebral column.
The sacrospinous ligament is a triangular-shaped structure with its base attached to the anterior sacrum (S2-S4) and coccyx, and its apex attached to the isch...
The sacrotuberous ligament (STL) is a stabiliser of the sacro-iliac joint and connects the bony pelvis to the vertebral column.
The STL has a broad fan-like origin from the sacrum, coccyx, ilium and sacro-iliac joint capsule. Its fibres converge to course caudally to insert into...
The sacrum is the penultimate segment of the vertebral column and also forms the posterior part of the bony pelvis. It transmits the total body weight between the lower appendicular skeleton and the axial skeleton.
The sacrum is an irregularly-shaped bone, roughly an inverted tr...
SADDAN syndrome is an acronym for (severe achondroplasia with developmental delay and acanthosis nigricans). It is an extremly rare condition and as the name stands comprises of skeletal brain and cutaneous anomalies.
It (like achondroplasia) also results from a mutation i...
Saddle joints are a type of synovial joint that allow articulation by reciprocal reception. Both bones have concave-convex articular surfaces which interlock like two saddles opposed to one another.
Saddle joints allow movement with two degrees of freedom much like condyloid joints...
Saddle pulmonary embolism commonly refers to a large pulmonary embolism that straddles the bifurcation of the main pulmonary artery, extending into the left and right pulmonary arteries.
If large enough, it can completely obstruct both left and right pulmonary arteries resulting in right heart ...
The sagittal midline of the brain is one of the most important sectional planes in neuroimaging. A good working knowledge of the normal neuroanatomy of the sagittal midline is essential so that the subtle abnormalities that may manifest here can be recognised.
The neuroembryological development...
The sagittal suture runs in the midline between the two parietal bones.
fusion of the sagittal suture results in scaphocephaly
The sail sign on an elbow radiograph describes the elevation of the anterior fat pad to create a silhouette similar to a billowing spinnaker sail from a boat. It indicates the presence of an elbow joint effusion.
The anterior fat pad is usually concealed within the coronoid fossa or seen parall...
The Sakati-Nyhan syndrome, also known as Sakati-Nyhan-Tisdale syndrome or acrocephalosyndactly type III, is an extremely rare type of acrocephalopolysyndactyly.
Its main features include:
congenital limb abnormalities
congenital heart defects
History and etymology
Salivary gland tumours are variable in location, origin and malignant potential.
In general, the ratio of benign to malignant tumours is proportional to the gland size; ie: the parotid gland tends to have benign neoplasm, the submandibular gland 50:50 and the sublingual glands and a...
Only a minority of salivary gland tumour types show uptake on 99Tc scintigraphy
oncocytoma of salivary glands
haemangioendothelioma of salivary glands 1
The salivary glands within the head and neck secrete various enzymes useful for mastication and digestion. They can be divided into major and minor salivary glands:
Major salivary glands
The major salivary glands consist of the larger, paired salivary glands within the neck:
Salpingitis refers to inflammation of the fallopian tube, it can be a part of pelvic inflammatory disease.
salpingitis isthmica nodosa
Salpingitis isthmica nodosa (SIN), sometimes also referred to as perisalpingitis isthmica nodosa - PIN, refers to nodular scarring of the fallopian tubes. In very early stages, the tubes may appear almost normal. As scarring and nodularity progress, the changes become more radiographically appar...
The salt and pepper sign is used to refer to a speckled appearance of tissue. It is used in many instances, but most commonly on MRI. Please note that pathologists also use the term.
Used to describe some highly vascular tumours which contain foci of ha...
Salt and pepper sign or pepperpot skull of the calvarium refers to multiple tiny well defined lucencies in the skull vault caused by resorption of trabecular bone in hyperparathyroidism.
There is loss of definition between the inner and outer tables of the skull and a ground-glass appearance as...
The Salter-Harris classification was proposed by Salter and Harris in 1963 1 and at the time or writing (June 2016) remains the most widely used system for describing physeal fractures.
Conveniently the Salter-Harris types can be remembered by the mnemonic SALTR.
Useful mnemonics for remembering the Salter-Harris classification system is:
Fortunately this is also the order of prognosis (from best to worse)
S: slipped (type I)
A: above (type II)
L: lower (type III)
T: through or transverse or together (type IV)
Salter-Harris type I fractures are relatively uncommon injuries that occur in children. Salter-Harris fractures are injuries where a fracture of the metaphysis or epiphysis extends through the physis. Not all fractures that extend to the growth plate are Salter-Harris fractures.
Salter-Thompson classification for Legg-Calve-Perthes disease simplifies the Catterall classification into 2 groups. Based on the radiographic crescent sign, we can distinguish:
group a: including Catteral groups I and II, where the crescent sign involves less than 50% of the femoral head.
Sampson syndrome refers to a type of superficial endometriosis, where multiple superficial plaques may be seen scattered in the peritoneum and pelvic ligaments.
The patient may present with non-specific abdominal pain.
At laparoscopy, they are typi...
Samter syndrome, also know as aspirin or analgesic-induced asthma refers to the constellation of 1-2:
allergy to aspirin
nasal polyposis / rhinosinusitis
Treatment and prognosis
Treatment is largely centred around avoiding aspirin, treating underlying asthma and if need be polypectom...
A sandal gap deformity is an imaging observation in antenatal ultrasound (typically second trimester) where there is an apparent increase in the interspace between the great toe of the foot from the rest of the toes (likened to the gap caused by a sandal).
While it can be a normal variant (esp...
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words after bullets should not be capitalized until they represent a name, e.g. Churg-Strauss syndrome will have "C" an...
The Sanders classification system is used to asses intraarticular calcaneal fractures, which are those involving the posterior facet of the calcaneus. This classification is based on the number of intraarticular fracture lines and their location on semicoronal CT images. This classification is u...
A sandwich sign, sometimes known as a hamburger sign, refers to a mesenteric nodal mass, either para-aortic or not, giving an appearance of a hamburger. Confluent lymphadenopathy on both sides of the mesenteric vessels gives rise to an appearance described as the sandwich sign 2.
The sign is sp...
Sandwich sign of Marchiafava-Bignami disease is described as the appearance due to involvement of central layers of corpus callosum.
T2 and FLAIR hyperintensities are seen in the central region of body and splenium of corpus callosum with sparing of peripheral dorsal and ventral layers of corpu...
Sandwich vertebral body is a radiologic appearance in which the endplates are densely sclerotic, giving the appearance of a sandwich.
This term and pattern is distinctive for osteopetrosis.
the sandwich vertebrae appearance resembles Rugger-jersey spine but can be diffe...
A santorinicoele refers to a cystic dilatation of the end of the dorsal pancreatic duct (duct of Santorini) 1,2 and is believed to be analogous to a dilatation of the most distal common bile duct, which is commonly known as a choledochocoele3.
It can occur in association with pancreas divisum...
The saphenous nerve is the continuation of the deep division of the femoral nerve in the femoral triangle.
runs within the subsartorial canal, giving off an infrapatellar branch (it also contributes to the subsartorial nerve plexus)
curves behind sartorius, appearing behind the ...
The SAPHO syndrome is an acronym that refers to a rare condition that is manifested by a combined occurrence of 2
It classically tends to present in young to middle-aged adults. Presentation in the paediatric pop...
Sappey plexus is a network of lymphatics in the areola of the nipple.
The breast is originally an ectodermal tissue, thus its lymphatic drainage is mostly parallel to the lymph flow of the overlying skin. Lymphatic flow from the skin finds its way to the diffuse subcutaneous plexus between the ...
Sarcoidosis is a non-caseating granulomatous multi-system disease with a wide range of clinical and radiographic manifestations.
Individual systemic manifestations are discussed individually:
pulmonary and mediastinal manifestations
Sarcoidosis is a systemic inflammatory disease of unknown origin characterized by the formation of non-caseating granulomas. Virtually any organ system may be involved. Although the involvement of abdominal viscera is less frequent than pulmonary and mediastinal disease when it occurs, it may m...
Cardiac manifestations of sarcoidosis are present in up to 25% of patients with sarcoidosis, but only 5-10% of patients are symptomatic 1-2.
Sarcoidosis is a multisystem disorder characterized by the presence of non-caseating granulomas. For a general discussion of this condition please refer t...
Head and neck manifestations of sarcoidosis can have three main forms:
orbital involvement: orbital sarcoidosis
parotid gland involvement
nodal involvement: cervical lymphadenopathy in sarcoidosis
Musculoskeletal manifestations of sarcoidosis occur in ~20% (range 4-38%) of patients with sarcoidosis and include joint involvement, bone lesions, and muscular disease. Approximately 25% of patients with sarcoidosis have associated arthropathy.
joints: joint involvement in sarcoido...
Orbital manifestations of sarcoidosis are common among patients with systemic sarcoidosis and can involve the lacrimal gland, the orbit, soft tissues of the orbit, and the optic nerve. Uveitis is by far the most common manifestation and is typically bilateral 5.
For a general discussion of the...
Pulmonary and mediastinal involvement of sarcoidosis is extremely common and is seen in over 90% of patients. Radiographic features are variable depending on the stage of the disease.
For a general discussion, please refer to the parent article: sarcoidosis.
Sarcomatoid renal cell carcinoma (sRCC) may develop when one of the more common subtypes of renal cell carcinoma degenerates into a sarcoma. It is generally irregular and malignant-appearing on imaging, but does not have specific imaging features.
The sarcomatoid variant has been ...
The sartorius muscle is the long obliquely oriented muscle of the anterior upper leg.
origin: anterior superior iliac spine
insertion: as part of the pes anserinus tendon, onto the medial superior tibia
primary: flexion of the hip and knee
secondary: lateral rotation and wea...
Satisfaction of search is a common error in diagnostic radiology. It occurs when the reporting radiologist fails to continue to search for subsequent abnormalities after identifying an initial one. This initial detection of an abnormalities satisfies the "search for meaning" and the re...
Saturation recovery (SR) sequences are rarely used for imaging now. Their primary use at this time is as a technique to measure T1 times more quickly than an inversion recovery pulse sequence. Saturation recovery sequences consist of multiple 90 degree RF pulses at relatively short repetition ti...
The term sausage digit refers to the clinical and radiologic appearance of diffuse fusiform swelling of a digit due to soft-tissue inflammation from underlying arthritis or dactylitis.
The common causes of sausage digit are :
sickle cell anemi...
The scalenus anterior (also known as anterior scalene) is a neck muscle and known as the "key" structure for the thoracic inlet as it is an important anatomical landmark.
origin: transverse processes of 3rd to 6th cervical vertebrae
insertion: inner border of first rib (s...
The scalenus medius (middle scalene) is one of the three scalene muscles in the neck.
origin: transverse processes of lower six cervical vertebrae (C2-C7)
insertion: upper surface of first rib
action (similar to scalenus anterior muscle)
raises first rib (respiratory inspiration)
The scalenus pleuraris muscle is an anatomical variant, being an accessory/supernumerary scalene muscle.
origin: anterior tubercle of C7
insertion: suprapleural membrane; inner border of first rib
has been noted as a cause of thoracic outlet syndrome
The scalenus posterior (posterior scalene) is one of the three scalene muscles in the neck.
origin: transverse processes of lower two or three cervical vertebrae (C5-C7)
insertion: outer surface of second rib
raises second rib (respiratory inspiration)
acting together: nec...
A scalp haematoma usually occurs following injury at delivery although they are increasingly seen with head trauma.
They can be subdivided by their location within the scalp, particular their location as related to the galea aponeurosis and skull periosteum (the SCALP mnemonic i...
The scalpel sign has been recently described in dorsal thoracic arachnoid web on sagittal MRI studies. It relates to focal distortion of the thoracic cord, appearing anteriorly displaced. The enlarged dorsal CSF space mimics the profile of a surgical scalpel.
It is helpful in distinguishing cas...
Scaphocephaly (also known as dolichocephaly) is the most common form of craniosynostosis, where premature closure of the sagittal suture results in impediment to lateral growth of the skull while anteroposterior growth continues, producing a narrow elongated skull. Causes are primary, or seconda...
The scaphoid (os scaphoideum) is the largest of the proximal row of carpal bones and forms the radial portion of the carpal tunnel. It is important for stability and movement at the wrist and may be fractured after a fall onto a hyperextended hand. Scaphoid fractures may be radiologically occul...
Scaphoid fractures (i.e. fractures through the scaphoid bone) are common, in some instances can be difficult to diagnose, and can result in significant functional impairment.
Scaphoid fractures account for 70-80% of all carpal bone fractures 1. Although they occur essentially at a...
Scaphoid fractures are the second commonest group of fractures that are seen following a fall onto an outstretched hand and result in wrist pain, specifically tenderness in the anatomical snuff box. They are particularly important because of the risk of avascular necrosis if displaced fractures ...
Mayo classification of scaphoid fractures divides them into three types according to anatomic location of the fracture line:
Fractures of the distal third are further divided into distal articular surface or the distal tubercle fractures:
The scaphoid lateral view is part of a four view series of the scaphoid, wrist and surrounding carpal bones. It is a complementary projection to the PA view demonstrating the scaphoid in the orthogonal plane.
patient is seated alongside the table
the affected arm if possible ...
Scaphoid non-union is one of the complications of scaphoid fracture because of the unique anatomy of the scaphoid and its vascular supply.
There are four types of non-union:
fibrous (delayed union): stable with no deformity or collapse
cystic: unstable and early collapse patterns
Scaphoid non-union advanced collapse (or SNAC wrist) is a complication that can occur with scaphoid fractures.
In a SNAC wrist, the proximal scaphoid fragment usually remains attached to the lunate (which rotate together during extension), while the distal scaphoid fragment rotates i...
The scaphoid series is comprised of a posteroanterior, oblique, lateral and angled posteroanterior projection. The series examines the carpal bones focused mainly on the scaphoid. It also examines the radiocarpal and distal radiocarpal joint along with the distal radius and ulna. Scaphoid fractu...
The oblique scaphoid view is part of a four view series of the scaphoid, wrist and surrounding carpal bones. The positioning is similar if not identical to the oblique wrist.
patient is seated alongside the table
the affected arm if possible is flexed at 90° so the arm and w...
The scaphoid PA axial view is part of a four view series of the scaphoid, wrist and surrounding carpal bones. It is a complementary projection to the PA view demonstrating the scaphoid free from superimposition.
patient is seated alongside the table
the affected arm if possib...
The scaphoid PA view is part of a four view series of the scaphoid, wrist and surrounding carpal bones. Although performed PA the view can often be referred to an AP view.
patient is seated alongside the table
the affected arm if possible is flexed at 90° so the arm and wrist...
Scapholunate advanced collapse (SLAC) refers to a pattern of wrist malalignment that has been attributed to post-traumatic or spontaneous osteoarthritis of the wrist.
It is often a consequence of a non-united scaphoid fracture or untreated scapholunate dissociation and rotatory sublu...
Scapholunate dissociation represents a significant ligamentous wrist injury that is important to identify on imaging. There is disruption of the scapholunate ligament with resultant instability. The condition may also be known as rotary subluxation of the scaphoid.
The scapholunate interval is the radiographic measurement of the scapholunate joint on PA wrist projections. Abnormal widening is indicative of injury to the scapholunate ligament that occurs with scapholunate dissociation.
In adults, the normal value is usually taken as < 2 mm, with an int...
The scapholunate ligament complex is a U-shaped ligamentous complex joining the lunate and the scaphoid.
It is divided into dorsal, volar and intermediate components with surrounding secondary stabilisers.
short, transverse collagen fibres
3 mm thick
Scaphotrapeziotrapezoidal (STT or triscaphe joint) arthritis is common, occurring in ~40% of wrist radiographs. It is typically degenerative (i.e. osteoarthritis) and presents with radial-sided wrist pain in patient over 50 years.
The scapula (plural: scapulae) is a roughly triangular shaped bone of the pectoral girdle with several articulations connecting to the humerus and clavicle.
The main part of the scapula, the body, consists of a somewhat triangular-shaped flat blade, with an inferiorly...
Scapula fractures are uncommon injuries, representing ~3% of all shoulder fractures.
Mechanisms of injury
requires high energy trauma (e.g. motor vehicle accidents account for 50% of scapular fractures)
direct trauma to the shoulder region
indirect trauma through falling on outstr...
The scapulothoracic joint is a not an anatomical joint as it does not refer to two opposing bones, but to a physiological joint of the pectoral girdle. The scapula is held against the thoracic wall by many muscles and the strut of the clavicle secondarily attaching it to the manubrium.
Scar endometriosis is a term given to endometriosis occurring in a Caesarian section scar. It can be located at the skin, subcutaneous tissue, rectus muscle/sheath, intraperitoneally, or in the uterine myometrium (within uterine scar).
The reported incidence of abdominal scar endo...
Scattering occurs when an ultrasound wave strikes a structure with both a different acoustic impedance to the surrounding tissue and a wavelength less than that of the incident ultrasound wave. Such structures are known as “diffuse reflectors,” with examples being red blood cells and non-smooth ...
The Scham sign of slipped capital femoral epiphysis is one of the subtle signs that may be seen on the AP view of an adolescent hip with early slip.
In the normal adolescent hip, an intraarticular portion of the diaphysis of the collum overlies the posterior wall of the acetabulum inferiomedial...
Schatzker classification system is one method of classifying tibial plateau fractures and splits the fracture into six types.
In the Schatzker classification, each increasing numeric fracture category indicates increasing severity, reflecting not only increased energy imparted to the bone at th...
A Schatzki ring, also called Schatzki-Gary ring, is symptomatically narrow oesophageal B-ring occurring in the distal oesophagus and usually associated with a hiatus hernia.
Relatively common, lower oesophageal rings are found in ~10% of barium swallows.