The retropharyngeal space (also known as the true retropharyngeal space to distinguish it from the danger space, which is sometimes referred to as part of the retropharyngeal space) is one of the seven deep compartments of the head and neck. It is a midline space that consists largely of fatty a...
Rhabdomyosarcomas of the orbit account for approximately 10-20% of all rhabdomyosarcomas and are usually found in children.
As with other locations, rhabdomyosarcomas in the orbit are overrepresented in males, and in Caucasians. They typically occur in children below the age of 1...
The rhinal sulcus is located on the anteromedial surface of the temporal lobe. It curves in an anteroposterior direction and separates the uncus from the temporal pole. Some sources consider it to be an extension of the collateral sulcus 1-4. The grey matter overlying the rhinal sulcus has been ...
Rhinocerebral mucormycosis refers to an uncommon form of invasive fungal sinus infection.
The presentation can vary, ranging from exophthalmos, rhinorrhoea, and ophthalmoplegia with loss of visual acuity and peripheral facial palsies occurring rarely 4.
Rhinoliths, also known as nasal calculi, are uncommon lesions that result from a chronic inflammatory response to complete or partial mineralised encrustation of intranasal foreign bodies. They are most commonly seen in children and cognitively impaired adults who accidentally insert foreign bod...
Rhinoscleroma is a chronic granulomatous infection involving the upper respiratory tract due to Klebsiella rhinoscleromatis. It initially involves the nasal mucosae but it may progress to any other part of the upper respiratory tract.
Untreated rhinoscleroma slowly progresses over many years 1....
Riedel thyroiditis is a very rare form autoimmune thyroiditis. It is sometimes considered as a manifestation of a wider systemic disease with fibrosis of the retroperitoneum, mediastinum, as well as lymphocytic infiltration of extraocular orbital muscles, salivary and lacrimal glands 4. Most rec...
Ritscher-Schinzel syndrome (RTSC), also known as 3C (cranio-cerebello-cardiac) syndrome, is a rare entity with a variable spectrum of CNS (primarily cerebellar), craniofacial, and congenital heart defects.
Robin sequence, also called Pierre Robin syndrome or Pierre Robin anamaloid, is a congenital condition characterised by facial abnormalities. Its aetiology has no genetic base, but rather, is reliant on a sequence of events, one following the other.
Robin sequence is the preferred ...
Romana sign, also known as chagoma, refers to periorbital swelling, palpebral oedema and conjunctivitis seen 1-2 weeks following infection with Trypanosoma cruzi (causative agent in Chagas disease).
Romana sign is associated with ipsilateral regional lymphadenopathy.
History and etymology
Rosai-Dorfman disease, also known as sinus histiocytosis with massive lymphadenopathy, is a rare benign idiopathic proliferative disease that involves phagocytic histiocytes.
The disease predominantly occurs in young adults with a mean age at presentation of 21 years. There may be...
The round window is one of two openings in the middle ear, localised at the level of the cochlea, allowing communication between the middle and inner ear. It vibrates with opposite phase to vibrations from the inner ear, producing movement of perilymph in the cochlea.
It is locat...
The Roy-Camille classification of fractures of the odontoid process of C2 depends on the direction of the fracture line 1.
The level of fracture line as described by the Anderson and D’Alonzo classification, is not predictive of the degree of instability or the risk of non-union. This classific...
The saccule is a small membranous sac, paired with the utricle, within the vestibule of the ear. It has an important role in orientation and balance, particularly in vertical tilt 1.
The vestibule is located within the bony labyrinth of the inner ear 2 (inferior to the semicircul...
The sack of marbles sign refers to aggregations of multiple small globules of fat within a cyst mimicking marble spheres within a sack. They appear hyperechoic on ultrasound, fat attenuation on CT, and high signal on T1WI and T2WI on MRI. It is considered highly suggestive of a dermoid cyst 1.
The sagittal suture is the midline articulation that joins the two parietal bones.
premature fusion of the sagittal suture results in scaphocephaly
normal fusion of the sagittal suture occurs at approximately 22 years of age
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:
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; i.e. the parotid gland tends to have benign neoplasms, the submandibular gland 50:50, and the sublingual glands a...
Only a minority of salivary gland tumour types show uptake on 99Tc scintigraphy
oncocytoma of salivary glands
haemangioendothelioma of salivary glands 1
The salpingopharyngeus is a muscle of the head and neck, and one of the inner longitudinal muscles of the pharynx. The paired slender muscles create vertical ridges of mucous membrane in the posterior pharyngeal wall descending from the medial ends of the Eustachian tubes to the called the salpi...
Salt and pepper sign or pepper pot skull refers to multiple tiny well-defined lucencies in the calvaria caused by resorption of trabecular bone in hyperparathyroidism. There is a loss of definition between the inner and outer tables of the skull and a ground-glass appearance as well as spotty de...
Sarcoidosis is a non-caseating granulomatous multi-system disease with a wide range of clinical and radiographic manifestations.
Individual systemic manifestations are discussed in respective articles:
pulmonary and mediastinal manifestations
Head and neck manifestations of sarcoidosis can have three main forms:
orbital involvement: orbital sarcoidosis
parotid gland involvement
nodal involvement: cervical lymphadenopathy in sarcoidosis
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...
Scala media, also known as cochlear duct, is an endolymph filled cavity in the cochlea located between the scala vestibuli (upper) and the scala tympani (lower). It is separated from the scala vestibuli by Reissner's membrane (vestibular membrane). It houses the organ of Corti.
The scala tympani, also known as tympanic duct, is the inferiormost duct of the cochlea. It is filled with perilymph and communicates directly with the subarachnoid space.
It is separated from the scala media and scala vestibuli by the spiral lamina.
The scala vestibuli, also known as vestibular duct, is the superiormost duct of the cochlea. It is filled with perilymph and communicates directly with the subarachnoid space.
It is separated from the scala media by Reissner's membrane (vestibular membrane) and from the scala tympani by the spi...
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 (scalene tuberc...
The scalenus medius (middle scalene) muscle 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 inspirat...
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...
The scalp is the skin and subcutaneous tissue covering the neurocranium. It is composed of five layers and has a rich vascular supply which explains why it bleeds profusely and heals well.
The scalp is composed of five layers which are easily remembered with this mnemonic. From external...
A scalp haematoma usually occurs following an injury at delivery although they are commonly seen with head trauma.
There are three types of haematoma, which are defined by their location within the scalp, particular their location as related to the galea aponeurosis and skull pe...
Schneiderian epithelium/membrane is the unique lining of the nasal cavity and paranasal sinuses, and is an ectodermally derived ciliated columnar epithelium with goblet cells. It differs from the similarly appearing respiratory epithelium, which is endodermally derived.
Schneiderian papillomas are uncommon sinonasal tumours that arise from the sinonasal Schneiderian epithelium.
Schneiderian papillomas account for ~2.5% (range 0.4-4.7%) of sinonasal tumours 2.
There are three distinct histological types 1,2,3:
Scleritis refers to inflammation of the sclera. It has a wide range of causes.
It can affect age group but usually those between ages 30 and 50 years. There is a recognised increased female predilection (F:M of ~2:1).
Information on the pathogenesis of scleritis is lim...
Scleromalacia perforans (or non-inflammatory necrotising scleritis) is a severe and very rare form of scleritis.
systemic lupus erythematosus
Behçet disease 5
relapsing polychondritis 5
granulomatosis with p...
Sclerosing osteomyelitis of Garré is a specific type of chronic osteomyelitis. It mainly affects children and young adults. It typically affects the mandible and is commonly associated with an odontogenic infection resulting from dental caries.
Sclerosteosis is a rare autosomal recessive bone dysplasia resulting in sclerosis and hyperostosis, particularly of the skull, mandible and tubular bones. It is closely related to Van Buchem disease 1.
Sclerosteosis is a very rare disease, with only around 100 cases reported. Ther...
Sclerotic skull lesion can result from a number of causes. They include:
hyperostosis frontalis interna (normal variant)
lytic skull lesions
The scutum is a sharp bony spur that is formed by the superior wall of the external auditory canal and the lateral wall of the tympanic cavity. It forms the lateral margin of Prussak space.
acquired cholesteatoma: it is usually the first bony structure to be eroded by the enl...
Second branchial cleft cysts are a cystic dilatation of the remnant of the 2nd branchial apparatus, and along with 2nd branchial fistulae and sinuses accounts for 95% of all branchial cleft anomalies.
Although a congenital abnormality, they tend to present in early adulth...
Second branchial cleft fistulae are congenital anomalies of embryonic development of branchial apparatus with the external cutaneous ostium in the lateral neck connecting to the tonsillar fossa. They can be diagnosed as a result of typical clinical presentation and the diagnosis can be confirmed...
Semicircular canal dysplasia is relatively common of the labyrinthine anomalies. About 40% of patients with a malformed cochlea will have associated lateral semicircular canal (SCC) dysplasia.1 The other two common labyrinthine anomalies include SCC aplasia and SCC dehiscence.
The semicircular canals are components of the bony labyrinth along with the cochlea and vestibule.
There are three semicircular canals on each side:
superior semicircular canal: vertical plane
posterior semicircular canal: vertical plane
lateral semicircular canal: 30 degrees...
Senile calcific scleral plaques, also known as senile scleral plaques (SSP), are benign scleral degenerations common in elderly individuals. They are a common incidental finding on CT imaging.
The prevalence of SSP increases with age, from ~2.5% at age 60, to 25% at age 80 years a...
Sensorineural hearing loss (SNHL) refers to deafness secondary to conditions affecting the inner ear, internal acoustic canal, cerebellopontine angle, or vestibulocochlear nerve.
Conditions that cause SNHL can be divided by location:
otosclerosis (and othe...
Shock thyroid is an uncommon part of the hypovolemic shock complex.
It was initially described in 2016 as heterogenous thyroid contrast enhancement and fluid surrounding the thyroid in trauma CT of shocked patients without evidence for direct thyroid injury 2. Only 7 cases have been described ...
The short ciliary nerves are a group of nerves that branch from the nasociliary nerve in the intraconal space via the ciliary ganglion. Along with the long ciliary nerves, they supply sensation to the entire globe excluding the conjunctiva. The nasociliary nerve provides a small sensory componen...
A short maxillary length can result from many congenital and acquired causes. If seen in an antenatal ultrasound scan, it is often considered to have a high association with trisomy 21 1.
Many conditions that can cause midfacial hypoplasia will result in a short maxillar...
Sialadenitis refers to inflammation of the salivary glands. It may be acute or chronic and has a broad range of causes.
Patients may present with painful swelling of the concerned salivary gland, after eating (salivary colic). In bacterial sialadenitis, there may be a pu...
Sialectasis (siadochiectasis) is the cystic dilatation of the ducts within salivary glands. It is most commonly seen in the parotid gland and is associated with ascending infections and gland destruction.
Isolated, diffuse swelling of the affected salivary gland.
Sialoceles are cystic spaces (usually saliva containing) arising within a salivary gland.
They are essentially post- traumatic or iatrogenic in nature. The proposed mechanism includes laceration of the salivary glad duct or ductal stenosis with subsequent dilatation.
Sialography is the imaging of the salivary glands, most commonly the parotid gland. The salivary ducts are conventionally examined fluoroscopically with high sensitivity, though cross-sectional imaging with CT or MR sialography has also been described.
suspected sialolithiasis or s...
Sialolithiasis refers to the formation of concrements (sialoliths) inside the ducts or parenchyma of salivary glands and most commonly occurs in the submandibular glands and their ducts.
Sialolithiasis is the most common disease of salivary glands, accounting for approximately 50%...
Sialosis refers to diffuse, non-inflammatory, non-neoplastic recurrent enlargement of the major salivary glands. It is uncommon and has a variety of systemic causes.
The commonest causes are diabetes mellitus and alcoholism. Other causes include malnutrition, hormonal insufficiency and radiatio...
The sigmoid plate is variously described as the thin plate of bone between a high riding jugular bulb and the middle ear cavity (as shown in first image) or more generally as the thin bone separating the sigmoid sinus from adjacent structures (especailly mastoid air cells).
The wall of the ve...
The silent sinus syndrome represents maxillary sinus atelectasis that results in painless enophthalmos, hypoglobus and facial asymmetry 1-3. Some authors restrict the term to patients with no history of sinusitis, trauma or surgery 2.
Silent sinus syndrome usually presents in the ...
Sincipital encephalocoeles are congenital herniations of cerebral parenchyma through a cranial defect. There are three main types 1,2:
frontonasal encephalocoele (~50%): more common in Asia and Latin America 4
naso-ethmoidal encephalocoele (30%): more common in North America 4
Sinonasal adenocarcinomas are primary tumours of the sinonasal region with glandular differentiation. They are grossly classified as salivary and non-salivary subtypes. However, generally in the literature and IARC/WHO classification, the term Sinonasal adenocarcinoma refers to non-salivary aden...
The nasal passage and paranasal sinuses (collectively sinonasal) plays host to a number of diseases and conditions, which can be collectively termed sinonasal disease. One way of classifying separate entities is as follows:
inflammatory and infective conditions
Sinonasal lymphoma refers to the involvement of the nasal cavity and/or paranasal sinuses with lymphoma. It can be primary or secondary.
Presenting symptoms of sinonasal lymphoma are variable but are usually similar to those of benign inflammatory diseases. The clinical s...
Sinonasal mucosal melanoma (SNMM) is a very rare and unique subtype of malignant melanoma.
SNMMs account for ~1% of malignant melanomas and <4% of head and neck cancers 1,2. They affect older patients (60-90 years old) 2. There is a higher incidence in Japan 5.
Sinonasal polyposis refers to the presence of multiple benign polyps in the nasal cavity and paranasal sinuses.
It is most commonly encountered in adults and rare in children. Polyps are the most common expansile lesions of the nasal cavity 8. Incidence increases in patients with ...
Sinonasal respiratory epithelial adenomatoid hamartoma (REAH) is a rare benign glandular neoplasm of the sinonasal cavities. It is most commonly encountered within the olfactory clefts.
It is most often encountered in middle-aged adults with no definite gender predilection 1,2.
Sinonasal undifferentiated carcinoma (SNUC) is a rare and highly aggressive neoplasm arising in the paranasal sinuses. It has recently been characterised as a distinct pathologic entity.
Tumours tend to be rather advanced at presentation.
Sinus lateralis is a general term used to described a space behind and/or superior to the ethmoid bulla. As it actually refers to both the suprabullar and retrobullar recesses, the use of these more specific terms is preferred.
Sinus pericranii is a cranial venous anomaly in which there is an abnormal communication between intracranial dural sinuses and extracranial venous structures, usually via an emissary transosseous vein.
It is considered a type of low flow vascular malformation. It occurs in close communication ...
The Sistrunk procedure consists of removing a thyroglossal duct cyst and surrounding tissues.
The rationale for this procedure is that cure of the thyroglossal duct cysts will be unsuccessful unless the epithelium-lined tract (extending from the cyst to the foramen caecum) is completely remove...
The sitting duck appearance denotes the normal anatomical configuration of the jugular foramen:
the head of the duck (pointing backwards on the right side) represents the anteromedial pars nervosa
the body of the duck representing the pars vascularis
Sjögren syndrome is an autoimmune condition of exocrine glands that produce tears and saliva.
Sjögren syndrome is the second most common autoimmune disorder after rheumatoid arthritis. There is a recognised female predilection with F:M ratio of ≈ 9:1. Patients typically present a...
The skull AP view is a nonangled AP radiograph of the skull. This view provides an overview of the entire skull rather than attempting to highlight any one region.
the back of patient's head is placed against the image detector
The skull base angle allows the diagnosis of platybasia and basilar kyphosis. There are several different techniques that may be used on sagittal images from MRI or CT.
Angle formed by:
line joining the nasion with the centre of the pituitary fossa
line joining the anteri...
A useful mnemonic to remember the six skull bones is:
STEP OF 6
6: number of skull bones
The Caldwell view is a caudally angled PA radiograph of the skull, designed to better visualise the paranasal sinuses, especially the frontal sinus.
the patient is seated in front of the upright detector
the patient's forehead is placed against the image detector
Skull landmarks of anatomic importance exist, located where there is a palpable bony protuberance or where sutures join:
They are surgical landmarks and craniometric points, used for radiological or ...
The skull PA view is a non-angled PA radiograph of the skull. This view provides an overview of the entire skull rather than attempting to highlight any one region.
the patient is erect
the patient's forehead is placed against the image detector allowing for the nose to be in...
The Towne view is an angled AP radiograph of the skull, used to evaluate for fractures of the skull and neoplastic changes
the patient's nuchal ridge is placed against the image detector
the infraorbitomeatal line (IOML) is perpendicular to the image receptor
Skull tumours can be (as with tumours anywhere else) both primary and secondary, and benign or malignant.
giant cell tumour (GCT)
aneurysmal bone cyst (ABC)
epidermoid and dermoid cysts
The occipitomental (OM) or Waters view is an angled PA radiograph of the skull, with the patient gazing slightly upwards. It can be used to assess for facial fractures, as well as for acute sinusitis. Skull radiographs, in general, are rapidly becoming obsolete, being replaced by much more sensi...
The small communicating branch of the ciliary ganglion is a small branch of the nasociliary nerve which supplies sensory fibres through the ciliary ganglion. These fibres do not synapse in the ganglion but pass directly into the short ciliary nerves to supply sensation to the sclera, cornea, iri...
Snake-eye appearance refers to symmetric bilateral T1 hypointensity/T2 hyperintensity of the anterior horn of the grey matter on axial cervical MRI, evocative of a pair of snake's eyes.
It can be seen in late phase CT myelography, an all but forsaken technique, where it is also known as fried e...
Snake eyes is a term used to refer to the appearance of the facial nerve on coronal CT within its canal in the petrous temporal bone as the tympanic segment doubles back next to the labyrinthine segment adjacent to the cochlea. Anteriorly, these two segments converge at the geniculate ganglion.
The soft palate is the posterior part of the palate that is a mobile fold of soft tissue attached to the posterior border of the hard palate which laterally fuses with the lateral wall of the oropharynx. On its inferior oral surface it is lined by oral mucosa (which contains innumerous palatine ...
Soft-tissue sarcomas are a heterogeneous group of malignant tumours of mesenchymal origin (sarcoma) that originate from the soft tissues rather than bone. They are classified on the basis of tissue seen on histology. The commoner sarcomas in the adult and paediatric population are listed below.
Solitary bone cysts of the mandible (also known as traumatic bone cyst of the jaw, haemorrhagic cyst of the mandible, extravasation cyst, progressive bone cavity or unicameral bone cyst) are an uncommon nonepithelial lined lucent mandibular lesion. It is one of a myriad of potential mandibular l...
Solitary median maxillary central incisor (SMMCI) is a rare dental anomaly. It is usually considered as a minor manifestation (variant) of holoprosencephaly (HPE).
It is estimated to occur in 1:50,000 live births.
It is a complex disorder consisting of multiple, mainly...
Lymphadenopathy is quite common, and it can be very difficult to differentiate malignant lymphadenopathy from reactive nodal enlargement.
Several gray scale and colour Doppler features favour malignancy in a lymph node.
Gray scale parameters that favour malignancy
size: larger-more likely mal...
Sphenoethmoidal air cell, also commonly known as the Onodi air cell, is an anatomical variant of the paranasal sinuses, important due to its close proximity to the optic nerve and internal carotid artery.
The sphenoethmoidal air cell is generally defined as the posteriormost ethmoi...
The sphenoethmoidal recess drains the posterior ethmoid air cells and sphenoid sinuses into the superior meatus of the nasal cavity.
patterns of sinonasal obstruction
The sphenoethmoidal suture marks the osseous union between the crest of sphenoid bone and the perpendicular and cribiform plates of ethmoid bone.
The sphenofrontal suture is a cranial suture where the frontal bone meets the sphenoid bone bilaterally. From an anterior perspective of the skull, this suture appears in the roof of the bony orbits. From a lateral perspective, it appears as the meeting of the inferoposterior edges of the fronta...
The sphenoidal ridge is the sharp curving line along the superior border of the greater wing of the sphenoid bone, separating the horizontal posterior part of the anterior cranial fossa in front from the vertical anterior wall of the middle cranial fossa behind.
The sphenoid bone is located at the base of skull.
Parts of the sphenoid bone include:
process and plates
The sphenoid bone articulates with twelve bones. Unpaired bones include: frontal, ethmoid, vomer, and occipital. Paired bone...