The masseteric nerve or nerve to masseter is a motor branch of the anterior division of the mandibular division of the trigeminal nerve.
The masseteric nerve divides off the anterior division and continues lateral to the lateral pterygoid muscle and then medially through the mand...
The masticator space is one of the seven deep compartments of the head and neck.
The masticator space are paired suprahyoid cervical spaces on each side of the face. Each space is enveloped by the superficial (investing) layer of the deep cervical fascia.
The superficial layer ...
The mastoid air cells (cellulae mastoidae) represent the pneumatisation of the mastoid part of the temporal bone and are of variable size and extent.
At the superior and anterior part of the mastoid process the air cells are large and irregular and contain air, but toward the in...
The mastoid foramen is a variably present foramen as well as being variable in its size, number and position. Most commonly, it is located near the posterior margin of the mastoid process, within the temporo-occipital suture.
It transmits the emissary veins connecting to the sigmoid sinus and a...
The mastoid part of the temporal bone is its posterior component.
The mastoid part is normally pneumatised by the mastoid air cells and is perforated by the mastoid foramen. The roof of the mastoid antrum, which separates the mastoid from the cranial cavity, is called the tegment...
Mastoidectomy is a fairly frequent procedure performed for a variety of temporal bone pathologies including mastoiditis and cholesteatoma. It involves removing part of the bony wall of the mastoid to aid in drainage and surgical excision.
Types of mastoidectomy
A number of procedures have been...
The maxilla (or maxillary bones) is a pair of symmetrical bones joined at the midline, which forms the middle third of the face. It forms the floor of the nasal cavity and parts of its lateral wall and roof, the roof of the oral cavity, contains the maxillary sinus, and contributes most of the i...
Maxillary antral carcinomas are an uncommon head and neck malignancy. They usually present late despite growing large since they remain confined to the maxillary sinus and produce no symptoms.
Most commonly affects patients over 45 and has a strong male predilection (M:F = 5:1). M...
The (internal) maxillary artery is the larger of the two terminal branches of the external carotid artery.
Origin and course
The maxillary artery's origin is behind the neck of the mandible, at first, it is embedded in the substance of the parotid gland. From there it passes anterior between ...
The maxillary line is a mucosal projection along the lateral nasal wall corresponding to lacrimomaxillary suture externally. The midportion of the line is called "M point". During endoscopic sinus and orbital procedures the maxillary line and M-point are very important and useful landmarks in pa...
The maxillary sinus (or antrum of Highmore) is a paired pyramid-shaped paranasal sinus within maxillary bone which drains via maxillary ostium into infundibulum, then through hiatus semilunaris into the middle meatus of the nose. It is the largest of the paranasal sinuses. It is present at birth...
Maxillary tori are analogous to mandibular tori and are composed of densely mineralised bone usually devoid of a medullary cavity. Unlike in the mandible, where they arise on the inner surface, when arising from the maxilla they may project both inwards (in which case they arise from the midline...
The McGill Thyroid Nodule Score (MTNS) is a scoring system developed to estimate the risk of malignancy of thyroid nodules.1
The MTNS is based on 22 parameters:
eight clinical or laboratory parameters
gender (male): 1 point
age (>45 years old): 1 point
palpable nodule (prese...
McRae line is a radiographic line drawn on a lateral skull radiograph or midsagittal section of CT or MRI, joining the basion and opisthion.
Normal position of the tip of dens is 5mm below this line. If the tip of the dens migrates above this line it indicates the presence of basilar invaginati...
Medial canal fibrosis is characterised by fibrous tissue formation in the medial part of the bony external auditory canal.
Patients can present with conductive hearing loss, otorrhea and/or a history of chronic otitis.
The medial pterygoid muscle is one of the muscles of mastication.
The medial pterygoid muscle is a thick and square shaped muscle. It has two heads of origin. The deep head is the major component of the origin and is attached to the medial aspect of the lateral pterygoid plate o...
The medial rectus muscle is one of the 6 extra-ocular muscles that control eye movements.
innervation: inferior branch of the oculomotor nerve (CN III)
origin: Annulus of Zinn (tendinous ring)
insertion: globe (anterior, medial surface)
primary function: one of three ocular adductor...
A useful mnemonic to remember the bones forming the medial wall of the orbit is:
My Little Eye Sits (in the orbit)
M: maxilla (frontal process)
E: ethmoid (lamina papyracea)
S: sphenoid (body)
Medical devices in the neck are regularly observed by radiologists on plain film and CT reporting. They include devices which pass through the neck onto the chest and stomach.
Vascular access devices
peripherally inserted central catheters (PICC)
central venous catheters
Medication-related osteonecrosis of the jaw (MRONJ) describes the bony destruction of the jaw with exposed bone present for greater than eight weeks in the presence of current or previous antiresorptive and/or antiangiogenic medication use, and in the absence of radiation therapy to the head and...
Medullary thyroid carcinoma (MTC) is a subtype of thyroid cancer which accounts for 5-10% of all thyroid malignancies. It occurs both sporadically (80%) and as a familial form.
In nonfamilial cases it typically peaks in the 3rd to 4th decades.
Thought to arise from par...
Melanotic neuroectodermal tumour of infancy (MNTI) is a rare pigmented tumour that primarily affects the calvarium or facial skeleton of children, typically during infancy. It is usually a benign tumour, albeit locally aggressive.
Most cases are diagnosed during infancy, usually w...
Melkersson-Rosenthal syndrome (MRS), also known as cheilitis granulomatosa or Miescher-Melkersson-Rosenthal Syndrome, is a rare condition of unknown aetiology characterised by:
granulomatous inflammation of the face and lips (non-caseating)
facial nerve (CN VII) paralysis (involvement of crani...
Ménière disease (or idiopathic endolyphatic hydrops) is an inner ear disorder and as such can affect balance and hearing.
One or both ears can be affected. The chief symptoms are:
vertigo (often attacks which can be incapacitating)
sensation of f...
The mental artery is a terminal branch of the inferior alveolar artery which itself is a branch of the first part of the maxillary artery. It emerges onto the face from the mandibular canal with the mental nerve at the mental foramen, and supplies muscles and skin in the chin region. The mental ...
The mental foramen is a small foramen on the anterior surface of the mandible, adjacent to root of the mandibular second premolar tooth. The mental nerve, a terminal branch of inferior alveolar nerve and the mental artery leave the mandibular canal through it.
The mental nerve is one of the two terminal branches of the inferior alveolar nerve, a branch of the posterior division of the mandibular division of the trigeminal nerve. It emerges from the mandibular canal anteriorly through the mental foramen and supplies the labial gingiva of the lower lip ...
A mesiodens is the most common supernumerary tooth and is located in the palatal midline between the two maxillary central incisors.
It is rare with an estimated prevalence of ~1% (range 0.09 to 2.2%) 3. There is an increased male predilection with a M F ratio of ~2.5:1.
Metastases to the thyroid are an uncommon cause of thyroid malignancy.
Metastases to the thyroid represent 1.4-3% of all malignancies 5. In autopsy series, the incidence is ~10% (range 2-24%) 1,5.
The most common sites of primary malignancy include (note these will v...
Meth mouth is the name given to the overt dental disease that is one of the signs of methamphetamine use.
Clinical examination often reveals blackened, stained, rotting or crumbling teeth. Serial studies only a few years apart may show a striking deterioration in the pati...
The metopic suture (also known as the median frontal suture) is a type of calvarial suture. It is often associated with frontal sinus agenesis or hypoplasia 7.
This suture runs through the midline across the frontal bone from the nasion to the bregma, although it may often be in...
MIBG scan is a scintigraphic study that uses metaiodobenzylguanidine labeled to Iodine-123 or Iodine-131. It is indicated in the investigation of phaeochromocytoma.
MIBG is positive in:
olfactory neuroblastoma 1
carcinoid tumour 4
Michel aplasia, also known as complete labyrinthine aplasia (CLA), is a congenital abnormality of the inner ear and is characterised by bilateral absence of differentiated inner ear structures with resultant anacusis. It should not be confused with Michel dysplasia.
Michel aplasia i...
Microgenia is a term meaning a small chin. It is somewhat related to but let distinct from the term micrognathia which means a small mandible.
Microgenia can be isolated or be associated with a numer of anomalies which include
camptomelic dysplasia 1
Microphthalmia essentially means small eyes. It is characterised by a small eye within a small orbit. It can be unilateral or bilateral. It is sometimes defined as a globe with a total axial length (TAL) that is at least two standard deviations below the mean for age.
Microtia refers to a small pinna of the ear, when is it completely absent it is termed anotia.
The estimated incidence at around 1:9000 live births. It is more common in males and there is a recognised right sided predilection.
Microtia can be associated ...
The middle cranial fossa is a butterfly-shaped depression of the skull base, which is narrow in the middle and wider laterally. It houses the temporal lobes of the cerebrum.
The middle cranial fossa can be divided into medial and lateral parts. In the medial part, the following s...
The middle ear (or tympanic cavity) is an-air filled chamber in the petrous part of the temporal bone that is split into two parts: the tympanic cavity proper (the space directly internal to the tympanic membrane) and the epitympanic recess or attic (the space superior to the membrane). It sits ...
Middle ear effusions are frequent in children due to prominent adenoids and horizontal Eustachian tubes. These do not require imaging, and can be treated expectantly / medically / surgically with gromits. Eustachian tube dysfunction is the accepted aetiology, with resorption of air and extravasa...
Development of granulation tissue in the middle ear cavity is a generalised response to injury/inflammation, chronic otomastoiditis. It can either be typical or go down the pathway of becoming a cholesterol granuloma.
Typical granulation tissue is common, more so than cho...
There are three ossicles (from lateral to medial):
Their role is to mechanically amplify the vibrations of the tympanic membrane and transmit them to the cochlea where they can be interpreted as sound. They are located in the middle ear cavity and articulate with each ot...
There are a range of middle ear tumours, which are more likely to be benign than malignant.
The three most common middle ear tumours are (not in any particular order as there are differences in the literature) 1-3:
glomus tympanicum paraganglioma
The middle meningeal artery branches off the first part of the maxillary artery. It passes vertically through the roots of the auriculotemporal nerve and enters the middle cranial fossa via the foramen spinosum. Here it gives off two branches - superior tympanic branch and ganglionic branch - be...
The middle meningeal nerve (which is also known as the meningeal branch of the maxillary nerve) is a branch of the maxillary division of the trigeminal nerve which supplies the dura of the middle cranial fossa.
The nerve divides off the maxillary division just before the foramen ...
The middle nasal concha is one of the conchae in the nose. It consists of the medial surface of the labyrinth of ethmoid which is a thin lamella that descends from the under surface of the cribriform plate, and ends in a free, convoluted margin.
It is rough, and marked above by numerous grooves...
The middle pharyngeal constrictor muscle is one of the pharyngeal constrictor muscles. Its primary action is constriction of the pharynx (in coordination with the superior pharyngeal constrictor and the inferior pharyngeal constrictor muscles) to deliver a bolus of food into the oesophagus.
The middle superior alveolar nerve, also known as the middle superior dental nerve, is the second branch of the infra-orbital nerve, from the maxillary division of the trigeminal nerve. It is the smallest of the superior alveolar nerves and contributes to the superior dental plexus.
Midfacial hypoplasia is a type of congenital facial anomaly and can be feature of a number of congenital syndromic anomalies. These include:
chromosome 1p36 deletion syndrome 2
chromosome 18q deletion syndrome
fetal alcohol syndrome
fetal valproate s...
A variety of congenital midface anomalies occur in children. Although rare, these disorders are clinically important because of their potential for connection to the central nervous system. Lesions presenting as a midline nasal mass include:
nasal dermoid cyst...
Midline neck masses have a relatively narrow differential, as few structures are present in the midline. Dividing the causes according to structure of origin is a useful schema.
lymph node(s): Delphian node(s)
thyroglossal duct cyst
Mikulicz syndrome was considered a form of Sjögren syndrome (type 1) however more recently it is considered in IgG4 related disease spectrum. It is a non-specific inflammatory enlargement of at least two or more of the salivary and lacrimal glands with xerostomia.
It may also be referred to b...
Minor salivary gland tumours (MSGTs) are a subtype of salivary gland tumours originating from the minor salivary glands, which are found in the lips, tongue, and the mucosa of the oropharynx and larynx, among other locations.
MSGTs account for ~15% of all salivary gland tumours.
Minor salivary glands are a subset of the salivary glands. They are small and unnamed salivary glandular tissue scattered throughout the oral cavity and oropharynx as well as more widely in the mucosa of the aerodigestive tract.
They number in the hundreds and are important because salivary gl...
Mixed temporal bone fractures are a combination of longitudinal and transverse fracture types, and are probably the most common type. They frequently involve the otic capsule, and are associated with both conductive and sensorineural hearing loss.
petrous temporal bone fracture
The modified Memphis criteria are a set of screening criteria for blunt cerebrovascular injury (BCVI) in trauma. The presence of one or more of these criteria makes necessary a complementary CTA or DSA study to exclude a BCVI.
The screening protocol criteria for BCVI are:
base of skull fractur...
The modified Stenvers view is an oblique radiographic projection used to demonstrate the petrous temporal bone, IAM and bony labyrinth. It is primarily used to assess electrode placement following the insertion of a cochlear implant. Specifically it assesses the:
integrity, positioning, and dep...
The cochlear modiolus is a conical-shaped structure that consists of spongy (porous) bone located in the center of the cochlea which contains the spiral ganglion.
The spiral lamina projects from the modiolus.
Abnormality of the modiolus results in sensorineural hearing loss.
History and etymo...
Mondini malformation is a historical term used to described incomplete partition type II anomaly with large vestibular aqueduct.
The term is often used inappropriately to describe any cochlear abnormality, rather than a specific type of cochlear hypoplasia. Thus, most would favour not using the...
Morning glory syndrome refers to the combination of optic nerve head coloboma with associated midline structural abnormalities of the brain and skull. The name stems from the fundoscopic appearance that resembles the morning glory flower.
A mucocele simply refers to accumulation and expansion of a structure by mucus. It occurs in a variety of locations which are discussed separately:
paranasal sinus mucocele
oral cavity e.g. ranula, mucous retention cysts
mucocele of the appendix 1
mucocele of the gallbladder
mucocele of the...
Mucoepidermoid carcinoma is a tumour that usually occurs in the salivary glands. It can mimic most other tumours of the glands, and therefore is often considered in the differential.
Mucoepidermoid carcinomas are seen throughout all adult age groups, but are most common in middle...
Multinodular goitre (MNG) is defined as an enlarged thyroid gland (i.e. goitre) due to multiple nodules which may have normal, decreased or increased (toxic nodule) function. It is a slightly unhelpful term as some multinodular thyroids are not enlarged, resulting in the unwieldy term "multinodu...
Multiphase CT angiography is an evolving imaging technique in acute ischaemic stroke. The technique aims to quickly and reliably identify brain which is potentially salvageable with intervention. Brain tissue viability depends on many factors, with this technique assessing collateral leptomening...
The differential diagnosis for multiple cystic neck lesions is different to that for a solitary cystic neck mass.
Cystic neck lesions are seen in:
necrotic metastatic SCC nodes: older patient, M>F
papillary thyroid carcinoma metastases: usually a younger patient, F>M
Multiple endocrine neoplasia (MEN) syndromes are a collection of syndromes characterised by the presence of, as the name would suggest, multiple endocrine tumours. They are autosomal dominant in inheritance.
MEN I (Wermer syndrome)
MEN II (multiple endocrine adenomatosis)
MEN IIa (Sipple synd...
Multiple endocrine neoplasia (MEN) type I is also known as Wermer syndrome.
Primary hyperparathyroidism is one of the commonest presentations.
The abnormality is related to a tumour suppressor gene located in chromosome 11q13. MEN type I is an autosomal domina...
Multiple endocrine neoplasia (MEN) type II is also known as mucosal neuroma syndrome or multiple endocrine adenomatosis. It is a collection of syndromes characterised by the presence of multiple endocrine tumours.
They are autosomal dominant in inheritance, and share medullary thyroid carcinom...
Multiple endocrine neoplasia (MEN) type IIa, also known as Sipple syndrome, accounts for most cases of MEN II and is characterised by:
pheochromocytomas: in 50% of patients, often bilateral, and can be extra-adrenal
medullary thyroid cancer: 100% of patients, aggressive, and may secrete calcit...
Multiple endocrine neoplasia (MEN) type IIb, also known as mucosal neuroma syndrome 3, accounts for only 5% cases of MEN II and is characterised by:
pheochromocytoma(s): in 50% of patients, often bilateral, and can be extra-adrenal
medullary thyroid cancer: 100% of patients; aggressive, and ma...
Mumps is a (usually) self-limited viral infection that often occurs in epidemics among children. Its incidence has markedly diminished in countries with childhood vaccination programs, but can still be seen in patient who have not received vaccinations or who have waning immunity.
The muscle of the uvula or musculus uvulae is one of the 5 paired muscles of the soft palate.
origin: posterior border of the hard palate and the posterior nasal spine of the horizontal plate of the palatine bone
insertion: palatine aponeurosis and mucosa of the uvula
action: alters ...
The muscles of mastication can be divided into primary and secondary groups according to whether they connect the mandible directly to the skull or if they attach to other structures in the neck, e.g. hyoid, thyroid cartilage.
medial pterygoid muscle...
There are five paired muscles of the soft palate that are collectively referred to as the muscles of the soft palate or the palatal muscles:
tensor veli palatini
levator veli palatini
muscle of the uvula
All of them are innervated by the pharyngeal plexus ap...
The muscles of the tongue are divided into 2 groups each comprising 4 muscles. They are classified as intrinsic (to the tongue) and extrinsic muscles. They allow for the complex movements of the tongue and are all innervated by the hypoglossal nerve (CN XII) except one:
intrinsic muscles of th...
A handy mnemonic to recall the muscle attachments of the hyoid bone. The first sentence is for six muscles attaching superiorly, the second sentence is for three muscles attaching inferiorly. Both sentences are in order from lateral to medial:
Christopher, He Didn't Screw Girls Much. That's Obv...
The muscular triangle is one of the paired triangles in the anterior triangle of the neck. The triangles of the neck are surgically focussed, first described from early dissection-based anatomical studies which predated cross-sectional anatomical description based on imaging (see deep spaces of ...
Mylohyoid boutonniere is a normal focal discontinuity in the mylohyoid muscle, which may permit the sublingual salivary gland, fat or vessels - or a combination thereof - to protrude out from the sublingual space into the submandibular space.
The finding has been observed in up to...
The mylohyoid muscle is a paired muscular sling that forms part of the floor of the mouth. It also separates the sublingual space (and oral cavity) from the submandibular space.
origin: mylohyoid line/ridge on the medial surface of the mandible
insertion: midline raphe that extends f...
Myoepitheliomas and malignant myoepitheliomas were considered a variant of pleomorphic adenomas until 1991. However, these are also found in breast and bronchus and have gained recognition as separate entities. They account for less than 1% of salivary gland tumours, only rarely undergo malignan...
Myokymia refers to a fine undulating fascicular tremor of facial musculature which should be distinguished from hemifacial spasm which involves entire muscles rather than individual fascicles. The two conditions may co-exist.
The nasal bones are paired oblong upper central facial bones placed side by side between the frontal processes of the maxilla, jointly forming the nasal ridge.
The nasal bone has two surfaces:
external surface attaches the procerus and nasalis muscles
internal, which is transve...
Nasal bone fractures are the most common type of facial fractures, accounting for ~45% of facial fractures, and are often missed when significant facial swelling is present.
Unsurprisingly, nasal bone fractures occur when the nose impacts against a solid object (e.g. fis...
The nasal cavity forms part of the aerodigestive tract.
The nasal cavity is formed by 1:
anteriorly: nasal aperture
laterally: inferior, middle and superior nasal conchae or turbinates
superiorly: cribiform plate of the ethmoid bone
inferiorly: palatal processes of the maxill...
The nasal conchae are long, narrow curled shelves of bone that protrude into the nasal cavity. The superior, middle and inferior conchae divide the nasal cavity into four groove-like air passages.
The conchae are located laterally in the nasal cavity and covered by pseudostratified columnar, ci...
Nasal encephalocoeles are in most cases a form of neural tube defect particularly common in Southeast asia. They are are herniation of cranial content through a bony defect in the anterior skull base into the nasal area.
The term is variably used, but generally encompasses both frontoethmoidal ...
Nasal gliomas, also know as nasal glial heterotopia, are a rare congenital lesion composed of dysplastic glial cells which have lost their intracranial connections and present as an extranasal or intranasal mass.
Nasal gliomas are rare congenital lesions. These masses occur spora...
Nasal septal perforation may affect either the bony, or cartilaginous septum. Most commonly it affects the anterior septal cartilaginous area although with syphilis it characteristically affects the bony septum.
Symptoms include a nasal discharge, nasal congestion (loss o...
The nasal septum (Latin: septum nasi) separates the left and right nasal cavities. It extends from the nares anteriorly to the choanae posteriorly and is covered by squamous epithelium.
The nasal septum is comprised primarily of one cartilage and two bones. Anteriorly there is the se...
A not-very-useful mnemonic for the causes of nasal septum perforation is:
Say Water Coke Syrup Sugarwater Lemonade or Say Nothing
W: Wegener granulomatosis
N: non-Hodgkin T-cell lymphoma (NHL)
The nasal sill is the soft tissue ridge forming the posterior margin of the anterior naris. It also forms the caudal margin of the nasal vestibule.
The nasal sill forms part of the nasal base, which is defined as the inferior third of the nose when viewing the nose from below with the neck exte...
The nasal vestibule forms the small area just inside the anterior naris. It is formed by the columella medially, the nasal ala lateral and anteriorly and the nasal sill posteriorly.
The nasion is the midline bony depression between eyes where the frontal and two nasal bones meet, just below the glabella. It is also known as the bridge of the nose.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
The naso-orbital-ethmoid (NOE) region or interorbital region simply refers to the space between the orbits.
anterior: frontal process of the maxilla, nasal process of frontal bone, nasal bone
posterior: sphenoid sinus
lateral: medial orbital wall