The MacEwen triangle (also called the suprameatal triangle or mastoid fossa) is a small triangular depression affecting the inner table of the temporal bone.
The lines forming the triangle are:
anterior: posterior border of the external acoustic meatus
superior: posterior root of the zygomati...
The increased globe size or macrophthalmia may have many differentials:
buphthalmos (congenital glaucoma)
macrophthalmus in neurofibromatosis type 1 (NF1)
connective tissue disorders: Marfan syndrome, Ehlers-Danlos syndrome
Madelung disease, also known as Madelung-Launois-Bensaude syndrome or neck lipomatosis, is a rare benign entity clinically characterised by the presence of multiple and symmetric, non-encapsulated masses of fatty tissue, usually involving the neck and the upper region of the trunk.
The major salivary glands are the largest and most important of the salivary glands and comprise of:
paired parotid glands
paired submandibular glands
paired sublingual glands
salivary gland tumours
Malignant mixed tumours of salivary glands, according to the WHO classification, comprise three tumours:
carcinoma ex pleomorphic adenoma
arises from pre-existing pleomorphic adenoma
carcinosarcoma (true mixed tumour of the salivary glands)
true malignant mixed tumour
99% also ...
Malignant salivary gland tumours are staged using the TNM staging system:
Tx: primary tumour cannot be assessed
T0: no evidence of primary tumour
less than or equal to 2 cm in maximal diameter
no extra-parenchymal extension
2-4 cm in maximal diameter
The malleus is the lateral most middle ear ossicle, located between the tympanic membrane and the incus.
The malleus has a head, neck, and three distinct processes (manubrium (handle), anterior and lateral processes).
The head is oval in shape, and articulates posteriorly with t...
The mandible is the single midline bone of the lower jaw. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles (angle of the jaw). It articulates with both temporal bones at the mandibular fo...
The mandibular canal is located within the internal aspect of the mandible and contains the inferior alveolar nerve, artery and the vein. It starts at the mandibular foramen, on the lingual side of the ramus, continues on buccal surface of body of the mandible and ends at the mental foramen, adj...
The mandibular foramen or inferior alveolar foramen is located on medial surface of ramus of the mandible and is the entrance to the mandibular canal. It transmits inferior alveolar nerve, a branch of the posterior division of the mandibular division of the trigeminal nerve that supplies all the...
The mandibular fossa is the smooth concave articular surface formed by both the squamous and petrous parts of the temporal bone. It is a part of temporomandibular joint and lodges the condyle of mandible.
Mandibular fractures are relatively common especially among young men. Although traditionally the mandible and base of skull are thought to form a complete bony ring, interrupted only by the TMJs. This should mean that the mandible should fracture in two places (akin to the bony pelvis) making s...
Mandibular lesions are myriad and common. The presence of teeth results in lesions that are specific to the mandible (and maxilla) and a useful classification that defines them as odontogenic or non-odontogenic. While it may often not be possible to make a diagnosis on imaging alone, this classi...
Mandibular osteoradionecrosis (ORN) is more common after radiation therapy for head and neck malignancies due to the superficial position of mandible, which makes it exposed to high radiation. The maxilla can also be involved, but this is less frequent.
Mandibular ORN may occur i...
There are many causes for mandibular periostitis:
Langerhans cell histiocytosis
malignancy (both primary and metastatic)
necrosis, e.g. radiation osteonecrosis
Garre's sclerosing osteomyelitis
Mandibular tori are common benign outgrowths of bone from the inner surface of the mandible.
They are composed of compact bone, densely mineralized usually without medullary cavity, and arise from the inner surface of the mandible above the origin of mylohyoid. They are usually bilateral.
Marine-Lenhart syndrome refers to a variant of Graves' disease where there are coexistent autonomous thyroid nodules. It is better described as Graves' disease with coexistent with multinodular goiter or nodular Graves' disease 1, as most authors consider it a distinct sub-entity of Graves’ .
Marjolin ulcers reflect malignant degeneration within pre-existing scars or areas of chronic inflammation such as burns, venous ulcers, etc.
The Markowitz and Manson classification system categorises fractures of the naso-orbitoethmoid (NOE) complex as follows 1:
type I - in which the medial canthal tendon is intact and connected to a single large fracture fragment
type II - the fracture is comminuted, and the medial canthal tendon...
The masseter muscle is one of the muscles of mastication. It is rectangular shaped and consists of three layers of fibres, where the superficial layer is the largest.
origin: zygomatic arch
insertion: ramus and angle of mandible
innervation: masseteric nerve from the anterior divisio...
The masseteric artery is a small branch from the second part of the maxillary artery. It passes laterally through the mandibular notch to the deep surface of the masseter muscle. It supplies the muscle, and anastomoses with the masseteric branches of the external maxillary and with the transvers...
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 the mastoid foramen.
The mastoid part has an outer rough surface that provides attachment to occipitalis and auricularis ...
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/or surgical excision.
Types of mastoidectomy
A number of procedures have b...
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 it remains confined within the maxillary sinus and produces no symptoms.
Most commonly affects patients aged over 45 years and has a strong male predilection...
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 (pres...
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)
S: sphenoid (body)
This article contains a list of commonly used medical abbreviations and acronyms that may be encountered in medicine and radiology (please keep in alphabetic order).
abdominal aortic aneurysm
acute anxiety attack
AAC: adenocystic carcinoma
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.
origin: greater cornu of the hyoid bone, lesser cornu and stylohyoid ligament
insertion: pharyngeal raphe
artery: pharyngeal branch of the ascending pharyngeal artery, tonsillar branch of the facia...
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...
Mondini malformation is an inner ear abnormality and is often used inappropriately to describe any cochlear abnormality, rather than a specific type of cochlear hypoplasia. Thus, most would favour not using the term, except perhaps in cases where the findings exactly match those described by Mon...
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 mucocoele simply refers to accumulation and expansion of a structure by mucous. It occurs in a variety of locations which are discussed seperately:
paranasal sinus mucocoele
oral cavity e.g. ranula, mucous retention cysts
mucocoele of the appendix 1
mucocoele of the gallbladder
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.
MNG is seen more commonly in females (M:F=1:3) in between 35-50 years of age, who present as nodu...
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.
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 3 muscles attaching inferiorly. The both sentences are in order from lateral to medial:
Christopher, He Didn't Screw Girls Much. That's Obv...
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 ...