The 2005 WHO histological classification of odontogenic tumours lays out a classification system for neoplasms and other tumours related to the odontogenic apparatus. At the time of writing (2016) it is still the most widely used classification system.
Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
central core comprised of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessels a...
The parietal and occipital bones in particular are common regions for accessory sutures because of their multiple ossification centres.
The occipital bone has complex development, ossifying from six centres. The foramen magnum is surrounded by four ossification centres. On each side are the exo...
Accessory parotid glands are a normal variant and represent ectopic salivary tissue present away and separate from the main parotid gland 1.
Accessory parotid glands are not rare and are seen in ~20% of the general population 2.
Located on the masseter muscle, ante...
Achondroplasia is the most common cause of short limb dwarfism. (For a general discussion, see the generic article on achondroplasia.)
As the skull base forms by endochondral ossification whereas the skull vault by membranous ossification there is a marked discrepancy in relative size as the sk...
Acinic cell carcinomas of the salivary glands are rare malignant neoplasms that account for 1-3% of all salivary gland tumours.
Pathology may superficially resemble normal serous (acinar) cells of the salivary glands. It is considered a low-grade, indolent malignancy, but with a ten...
Acoustic schwannomas (also known as vestibular schwannomas) are relatively common tumours that arise from the vestibulocochlear nerve (CN VIII) and represent ~80% of cerebellopontine angle masses. Bilateral acoustic schwannomas are strongly suggestive of neurofibromatosis type 2 (NF2).
Acquired cholesteatomas make up 98% of all middle ear cholesteatomas and are almost always closely related to the tympanic membrane, from which most are thought to arise.
The vast majority of acquired cholesteatomas develop as a result of chronic middle ear infection and...
Acrocephalopolysyndactyly (ACPS) syndrome is comprised of a rare group of disorders collectively characterised by:
calvarial anomalies: e.g. craniosynostoses
digital anomalies: syndactyly and polydactyly
While there can be some overlap in features, they can be primarily classified into the fo...
Acrocephalosyndactyly syndromes (ACS) is a rare group of disorders collectively characterised by:
calvarial anomalies, e.g. craniosynostoses
digital anomalies, e.g. syndactyly
While there can be some overlap in features, they can be primarily classified into the following majo...
Acute invasive fungal sinusitis is the most aggressive form of fungal sinusitis. It is seen particularly in immunocompromised patients and is the source of significant morbidity and mortality. It should be distinguished from the other two forms of invasive fungal sinusitis: chronic invasive fung...
Acute mastoiditis is largely a disease of childhood, and occurs when acute otitis media extends into the mastoid air cells.
When mastoiditis and acute otitis media occur concurrently, sometimes the term acute otomastoiditis is used.
When mucoperiosteal involvement evolves into b...
Acute sinusitis is an acute inflammation of the nasal and paranasal sinus mucosa that last less than four weeks and can occur in any of the paranasal sinuses.
Fever, headache, postnasal discharge of thick sputum, nasal congestion and abnormal smell.
Adenoid cystic carcinoma (ACC) are a rare histological subtype of adenocarcinoma.
ACCs are generally considered low grade 4. The tumors have notable tendency for perineural spread.
They have wide distribution and mainly occur in relation to the airways, lacrimal glands and...
Adenoid cystic carcinoma (ACC) of the lacrimal glands is an extraconal malignancy usually originating from the orbital lobe of the lacrimal gland.
It often presents with orbital pain and paresthesia, since this type of tumour is frequently associated with perineural sprea...
Adenoid cystic carcinoma (ACC) of the salivary glands is the second most common malignancy involving the parotid and the most common involving minor salivary glands.
ACCs arise more commonly in the minor salivary glands (~55%) than in the major salivary glands. They are locally aggre...
Adenoid facies refers to the long, open-mouthed face of children with adenoid hypertrophy. Hypertrophy of the nasopharyngeal pad of lymphoid tissues (the adenoids) is the most common cause of nasal obstruction in children. The mouth is always open because upper airway congestion has made patient...
Adenoidal hypertrophy or enlargement is common in childhood and is due to increase in size of the adenoid tonsils.
nasal congestion: adenoid facies
chronic or recurrent otitis media due to their proximity to the Eustachian tubes
Adenolipoma of the thyroid gland (also known as a thyrolipoma or a thyroid hamartoma) is a benign rare fat containing thyroid lesion. These lesions are usually well encapsulated and are composed of varying degrees of thyroid glandular tissue and fat tissue; the amount of fat can markedly vary (...
Adenomatoid odontogenic tumours are rare and differ from most other dentition related lesions in that they more frequently occur in the maxilla.
They are also seen more frequently in females, most frequently in the second decade of life.
They present as an...
Adrenal vein sampling (AVS) is a procedure used to confirm autonomous hormone production, if it is unilateral or bilateral, to guide further treatment.
AVS is commonly performed in primary aldosteronism, being indicated to identify aldosterone-secreting adenomas and to differentiate...
Agger nasi air cells are the most anterior ethmoidal air cells lying anterolateral and inferior to the frontoethmoidal recess and anterior and above the attachment of the middle turbinate. They are located within the lacrimal bone and therefore have as lateral relations the orbit, the lacrimal s...
Allergic fungal sinusitis (AFS) is the most common form of fungal sinusitis, and is common in warm and humid climates. On imaging, it usually presents as opacification and expansion of multiple paranasal sinuses, unilaterally or bilaterally, with content that is centrally hyperdense on CT. MRI s...
Allgrove syndrome (also known as triple A syndrome) is an autosomal recessive condition that consists of three main findings:
Alport syndrome is an X-linked recessive disease characterised by:
sensory neural hearing loss: typically high frequency 2
anterior lenticonus: most common ocular abnormality; may result in cataracts
perimacular pigmentary changes
flecks around the fovea 2...
Amaurosis fugax is the transient mono-ocular loss of vision, normally lasting a few seconds to a few minutes, and is secondary to vascular ischaemia/insufficiency. Usually the cause is ascribed to occlusion of the central retinal artery there are a wide number of local and central causes.
Ameloblastomas are locally aggressive benign tumours that arise from the mandible, or less commonly from the maxilla. Usually presented slowly but continuously growing hard painless lesion near the angle of the mandible in the 3rd to 5th decades of life which can be severely disfiguring if left ...
Anaplastic thyroid carcinoma (ATC) is a highly aggressive form of thyroid cancer and accounts for ~1-2% of primary thyroid malignancies. Of all the subtypes, this carries the worst prognosis.
Typically occurs in the elderly (peak incidence in 6th to 7th decades). A significant pro...
The anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge.
Head and neck anatomy
Abdominal and pelvic anatomy
Lower limb anatomy
Upper limb anato...
The ansa cervicalis is a component of the cervical plexus which gives muscular branches to the geniohyoid muscle of the suprahyoid group and all 4 of the infrahyoid muscles.
superior root: derived from the anterior primary rami of C1
inferior root: derived from the anter...
The anterior cervical space is a small infrahyoid compartment of the head and neck. It is a fat containing space and is not enclosed by fascia 1.
posterior: carotid space
medial: visceral space
superior: submandibular space
Anterior cord syndrome (also known as Beck's syndrome or anterior spinal artery syndrome) is a clinical subset of spinal cord injury syndromes, due to ischaemia/infarction of the anterior two-thirds of the spinal cord, typically sparing posterior third.
Patient present wi...
The anterior cranial fossa constitutes the floor of cranial vault which houses the frontal lobes of the brain.
Structures present in the midline of anterior cranial fossa from anterior to posterior are:
groove for superior sagittal sinus
groove for anterior meningeal vessels
The anterior jugular vein is a paired tributary of the external jugular vein.
Origin and course
The anterior jugular vein has its origin in the region of the hyoid bone or suprahyoid neck, as the confluence of several small superficial veins. It descends near the midline, medial...
The anterior lacrimal crest is a bony projection on the frontal process of the maxilla continuous with the orbital rim which creates the lateral margin of the lacrimal sac fossa. The medial palpebral ligament is attached to anterior lacrimal crest.
Immediately anterior to the anterior lacrimal ...
The anterior superior alveolar canal courses through the anterior wall of the maxillary sinus, and contains the anterior superior artery, vein and nerve. Usually, it shares a common channel with the infraorbital canal but when seen separately should not be confused for a fracture.
Antrochoanal polyps (ACP) are solitary sinonasal polyps that arises within the maxillary sinus but passes through and enlarges the sinus ostium and posterior nasal cavity to the nasopharynx.
Similar polyps can arise in the sphenoid sinus and extend into the nasopharynx, these are termed spheno...
An antrolith is a calcified mass within the maxillary sinus. The origin of the nidus of calcification may be extrinsic (foreign body in sinus) or intrinsic (stagnant mucus, fungal ball).
Most antroliths are small and asympotomatic. Larger ones may present as sinusitis with symptoms like pain a...
Arrested pneumatisation of the skull base is an anatomical variant that most commonly occurs in association with the sphenoid sinus. It is known that the sphenoid bones undergo early fatty marrow conversion antecedent to normal pneumatisation. However, for unclear reasons, some individuals exper...
The arteries of the head and neck are branches of the common carotid and and subclavian arteries.
(1st part) mandibular...
The arytenoid cartilages are paired cartilages that articulate with the sloping upper border of the lamina of the cricoid cartilage by the cricoarytenoid joint. This joint allows movement of the arytenoid cartilages, which is vital in approximating, tensing and relaxing the vocal folds.
The ascending cervical artery is 1 of the 4 branches of the thyrocervical trunk (off the first part of the subclavian artery).
It is a small artery that ascends medial to the phrenic nerve on the prevertebral fascia. It contributes many small spinal branches into the intervertebral foramina of ...
The ascending pharyngeal artery, the smallest branch of the external carotid, is a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid and under the stylopharyngeus.
origin: a branch of the external carotid artery
course: vertically with...
Assessment of thyroid lesions is commonly encountered in radiological practice.
hyperplastic / colloid nodule / nodular hyperplasia: 85%
papillary: 60-80% of carcinomas
Ultrasound along with nuclear medicine, is an important modality for assessment of thyroid lesions, and it is also frequently used to guide biopsy. Diagnostic criteria for thyroid nodules continue to evolve with improving ultrasound technology.
The asterion is the the star shaped junction on the side of the calvarium where 3 sutures meet:
It is located at the the posterior end of the parietomastoid suture, where as the pterion is located at the anterior end.
It is one of...
Asteroid hyalosis is a degenerative condition of the eye where there is accumulation of calcium soaps in vitreous chamber.
The prevalence increases with age from 0.2% 43-54 year olds to 2.9% in 75-86 year olds. The overall prevalence is 1.2%. It is more commonly unilateral and fav...
The American Thyroid Association (ATA) guidelines for assessment of thyroid nodules are meant to improve inter- and intra-reader consistency during assessment of thyroid nodules on ultrasound, and to facilitate communication with referring endocrinologists.
The 2015 guidelines stress the import...
The atlantodental interval (ADI), as the name suggests, is the horizontal distance between the anterior arch of the atlas and the dens of the axis, used in the diagnosis of atlanto-occipital dissociation injuries and injuries of the atlas and axis.
It is the distance (in mm) between the posteri...
This mnemonic helps when remembering the ascending order of structures that corresponds to each waveform in an auditory brainstem response (ABR) tracing:
E: eighth nerve action potential (wave I)
C: cochlear nucleus (wave II)
O: olivary complex (superior) (wave III)
An auricular pseudocyst is a rare and benign cystic swelling resulting from intracartilaginous accumulation of fluid within the pinna.
While it can occur at any age and in either gender, it typically presents in middle aged males with a mean age of presentation being around 35-40 ...
Autoimmune thyroiditises (AIT) refers to a group of conditions where there is inflammation involving the thyroid gland related to thyroid antibodies.
They are most common thyroid disease group in the paediatric population 5.
Entities that fall under this category inclu...
This classification was intially proposed by Bailey in 19292 and remains the most widely used classification system at time of writing (July 2016).
Bailey classification of second branchial cleft cysts provides a structure for classing second branchial cleft cysts into four types. It is no long...
The Ballet sign refers paralysis of voluntary movements of the eyeball with preservation of the automatic movements. Sometimes this sign is present with exophthalmic goitre and hysteria.
Barrow caroticocavernous fistula classification divides caroticocavernous fistulas into direct (type A) or indirect (types B-D). This classification was proposed by Barrow et al. in 1985 1 and at the time of writing (mid 2016) remains the most widely used system for describing caroticocavernous ...
The base of skull (or skull base) forms the floor of the cranial cavity and separates the brain from the structures of neck and face.
The base of skull is a bony diaphragm composed of number of bones including (from anterior to posterior):
The basion is the median (midline) point of the anterior margin of the foramen magnum.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
Various lines and measurements using the basion are made in the diagnosis of ...
The basion-axial interval (BAI), as the name suggests, is the horizontal distance between the basion and the posterior cortex of the axis, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance (in mm) between the basion and the superior extension of the posterior ...
The basion-dens interval (BDI), as the name suggests, is the distance between the basion and the tip of the dens, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance from the most inferior portion of the basion to the closest point of the superior aspect of the ...
A mnemonic used to remember the behavioural changes of obstructive sleep apnoea (OSA) is:
P: poor school performance
L: lack of concentration
Behçet disease is a multi-systemic and chronic inflammatory vasculitis of unknown aetiology.
The mean age at which Behçet disease occurs is 20-30 years. The disease is most prevalent in the Mediterranean region, Middle East and East Asia. The highest incidence has been reported in...
Benign lymphoepithelial lesions (BLL or BLEL), also misleadingly known as AIDS-related parotid cysts (ARPC), are mixed solid and cystic lesions that enlarge the parotid glands, and are usually associated with cervical lymph node enlargement, and nasopharyngeal lymphofollicular hyperplasia.
There are a number of benign metastasising tumours:
benign metastasising meningioma 1,2
benign metastasising leiomyoma 3
primary adenoma of thyroid 4
giant cell tumour of bone 5
Benign minor salivary gland pathology is a broad term that encompasses a number of relatively uncommon pathologies that affect the minor salivary glands of the head and neck:
salivary retention cysts
A Bezold abscess is a complication of acute otomastoiditis where the infection erodes through the cortex medial to the attachment of sternocleidomastoid , at the attachment site of the posterior belly of the digastric muscle, and extends into the infratemporal fossa. Due to it being deep to the ...
The Biffl scale or grade illustrates the spectrum of blunt cerebrovascular injury (BCVI) seen on angiography (both CTA and DSA). Some authors refer to the grading scale as the Denver scale, which is not to be confused with the Denver criteria, a set of clinical and risk factors for BCVI.
Bilateral thinning of the parietal bones, also known as biparietal osteodystrophy, is an uncommon, slowly progressive acquired disease of middle-aged people with slight female predilection. It is typically an incidental finding.
The aetiology is unknown but is thought to be an age-r...
Bill's bar is a landmark that divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment. Anterior to Bill bar, in the anterior superior quadrant, are the facial nerve (CN VII) and nervus intermedius, and posterior to it in the posterior superior ...
The bimastoid line has been described and used to evaluate basilar invagination on frontal skull plain film and coronal recontructed CT image.
The bimastoid line is drawn between right and left tip of mastoids. The tip of the odontoid process of C2 normally projects less than or equal to 10 mm...
The binocular distance (BOD) is a measurement between the two lateral (outer) canthi of each eye. It is sometimes used as a accessory fetal biometric parameter where it is often documented on both 2nd trimester anatomy scans on axial brain scans. The largest diameter of the orbit should be used ...
Black eyebrow sign is the description given on plain facial radiographs to intra-orbital air 1.
Air rises into the most superior aspect of the orbit, almost always in the context of a facial fracture, in a linear fashion, giving the appearance of a eyebrow. The fracture is usually an orbital bl...
The black turbinate sign refers to an area of non-enhancing mucosa on MRI in a patient with angioinvasive fungal sinus infection / rhinocerebral mucormycosis.
Mucormycosis is caused by fungi that include Mucor, Rhizopus, and Absidia species. It is seen in diabetic and immunocompromised patient...
Blunt traumatic neck injury is uncommon because it is usually protected by the head, shoulders, and chest. This term is generally used to refer to injuries of the neck besides to cervical spine injuries, which are common.
Blunt injury to the neck is most commonly from motor vehicle ...
The body of the sphenoid bone is a cubical portion, hollowed by the sphenoid air sinuses.
The body has superior, inferior, anterior, posterior, and lateral surfaces.
The superior surface features:
ethmoidal spine: prominent spine that articulates with the cribiform plate and g...
Bogorad syndrome also known as the syndrome of crocodile tears, is characterized by residual facial paralysis with profuse lacrimation during eating. It is caused by a misdirection of the regenerating autonomic fibers to the lacrimal gland instead of to the salivary gland.
Bouthillier et al described (in 1996) 1 a seven segment internal carotid artery (ICA) classification system. It remains the most widely used system for describing ICA segments at the time of writing (mid 2016).
There are few others classifications systems including proposed by Fisher (1938), Gi...
Brachycephaly refers to a calvarial shape where the bi-parietal diameter to fronto-occipital diameter approaches the 95th percentile. It can result from a craniosynostosis involving the bicoronal and/or bilambdoid sutures.
Brachycephaly can be associated with numerous ...
Useful mnemonics to remember the four branches of the thoracoacromial artery are:
CAlifornia Police Department
Cadavers Are Dead People
B: breast (pectoral)
CAlifornia Police Department
Branchial cleft anomalies comprise of a spectrum of congenital defects that occur in the head and neck.
The anomalies result from branchial apparati (six arches; five clefts), which are the embryologic precursors of the ear and the muscles, blood vessels, bones, cartilage, and mucosa...
Branchio-oto-renal (BOR) dysplasia is a rare syndromic disorder characterised by:
can involve the outer, middle, and inner ear associated with conductive, sensorineural, or mixed hearing impairment
branchial fistulae and branchial cleft cysts
The bregma is the midline bony landmark where the coronal and sagittal sutures meet, between the frontal and two parietal bones.
It is the anterior fontanelle in the neonate and closes in the second 2 (typically around 18 months after birth).
It is one of the skull landmarks, craniometric poin...
The buccal space (or buccinator space) is one of the seven suprahyoid deep compartments of the head and neck.
The buccal spaces are paired fat contained spaces on each side of the face forming cheeks. Each space is enveloped by the superficial (investing) layer of the deep cervi...
The buccinator artery is a small branch from the second part of the maxillary artery. It runs obliquely forward, between the medial pterygoid and the insertion of the temporalis, to the outer surface of the buccinator, to which it is distributed, anastomosing with branches of the facial artery a...
Buphthalmos is a descriptive term which simply means an enlarged eyeball or ocular globe (usually without deformation or and intrinsic mass lesion).
It typically manifests in infants and young children.
It usually indicates the presence of congenital (infantile) glauc...
Calcific tendinitis of the longus colli muscle is an inflammatory/granulomatous response to deposition of calcium hydroxyapatite crystals in the tendons of the longus colli muscle.
Patients can present with debilitating symptoms that are unrelated to the degree of calcif...
Numerous causes of calcification of the globe are encountered, varying from the benign to malignant. When calcification is seen of the posterior half of the globe, it could relate to any of the layers (scleral, choroidal or retinal), as it is not possible to separate them out on CT.
Calcifying epithelial odontogenic tumour, also known as a Pindborg tumour, is typically located in the premolar and molar region of the mandible, although up to a third are found in the maxilla.
Usually they are seen in the 4th to 6th decades. They are rare tumours.
A simple mnemonic to recall a list of commonly calcifying metastases is:
B: breast cancer
T: papillary thyroid cancer
O: ovarian cancer (especially mucinous)
M: mucinous adenocarcinoma (especially colorectal carcinoma)
Capillary haemangiomas of the orbit, also known as strawberry haemangiomas, on account of its colouring, or orbital infantile haemangiomas, are the most common orbital tumours of infancy, and unlike orbital cavernous haemangiomas, they are neoplasms rather than vascular malformations.
The Capp triad refers to the constellation of clinical and imaging findings in patients with spontaneous retropharyngeal haematomas, and consists of:
tracheal and oesophageal compression
anterior displacement of the trachea
subcutaneous bruising over the neck and anterior chest
Serum carcinoembryonic antigen (CEA) is a cell-adhesive glycoprotein that was discovered in colorectal cancer in 1965, and is hence one of the oldest and most used tumour markers. Its name derives from its normal expression in fetoembryonic liver, gut and pancreas tissue.
Normal range of CEA is...
Carcinogens are substances known to cause cancer. They include:
Nasopharynx / nasal passage
ionising radiation (not technically a substance)
polyaromatic hydrocarbons (PAH)
Carcinoma ex pleomorphic adenoma is the most common of three malignant mixed tumours of salivary glands, and are thought to arise from pre-existing pleomorphic adenomas (or benign mixed tumours) 1.
These tumours usually occur in older patients (6th to 8th decade), who have had a p...