The parotid gland consists of a superficial and deep lobe. Determining the location and extent of the lesions affecting the gland is an essential aspect of imaging and vital information which needs to be conveyed to the surgeon.
Method of evaluation
The following lines are proposed for differe...
Locked-in syndrome is one of the brainstem stroke syndromes and can occur as a result of a pontine stroke that damages the ventral brainstem and pyramidal bundles and corticobulbar tracts 5.
Individuals who are "locked-in" are conscious with preserved cognitive function b...
The long ciliary nerves are a group of nerves that branch from the nasociliary nerve in the intraconal space. Along with the short ciliary nerves, they supply sensation to the entire globe excluding the conjunctiva. Unlike the short ciliary nerves however, they bypass the ciliary ganglion and he...
Longitudinal temporal bone fractures are petrous temporal bone fractures that occur parallel to the long axis of the petrous temporal bone. Although more current classifications of the extent of temporal bone fractures focus on the integrity of the otic capsule rather than the fracture orientati...
Petrous temporal bone fractures are classically divided into longitudinal, transverse or mixed fracture patterns depending on the direction of fracture plane with respect to the long axis of the petrous temporal bone. Some features may aid in distinguishing them.
The longus capitis muscle is a prevertebral muscle of the neck that is innervated by muscular branches of the cervical plexus. In isolation longus capitis acts to laterally flex and rotate the head.
origin: anterior tubercles of C3-C6 transverse processes
insertion: inferior surface o...
The longus colli muscle is a prevertebral muscle of the neck that is innervated by the anterior rami of C2–C6 from the cervical plexus. Longus colli is a weak flexor the cervical spine and when contracting unilaterally it tilts and rotates the cervical spine to the ipsilateral side. Longus colli...
Low attenuation lymphadenopathy refers to abnormal lymph nodes that on CT appear to have lower attenuation than other soft tissues. This category can be split into two types:
cystic (necrotic) lymph nodes
metastatic carcinoma (or lymphoma)
infections (tuberculous or fungal)
Ludwig angina (cellulitis) refers to rapidly progressive inflammation of the floor of mouth, which is potentially life-threatening due to the risk of rapid airway compromise.
Largely due to the advent of antibiotics, the condition is uncommon in present day modern societies. Immu...
The Lund-Mackay score is a widely used method for radiologic staging of chronic rhinosinusitis 1.
When reading a CT scan of the paranasal sinuses and ostiomeatal complex, the reader assigns each sinus a score of:
0 (no abnormality)
1 (partial opacification) or
2 (complete opacification)
Lymph node enlargement (rarely lymphadenomegaly) is often used synonymously with lymphadenopathy, which is not strictly correct.
Lymphadenopathy (or adenopathy) is, if anything, a broader term, referring to any pathology of lymph nodes, not necessarily resulting in increased size; ...
The lymph nodes in the neck have historically been divided into at least six anatomic neck lymph node levels for the purpose of head and neck cancer staging and therapy planning. Differing definitions exist across specialties 1-4. The following is a synthesis of radiologically useful boundaries ...
Lymphoscintigraphy is a nuclear medicine technique to visualize regional lymphatic drainage, especially for mapping sentinel lymph nodes, from a site of radiopharmaceutical injection.
Colloidal agents are used as these particles enter lymphatic channels and migrate to lymph...
The lyre sign refers to the splaying of the internal and external carotid by a carotid body tumor. Classically described on angiography it is also visible on CT angiography.
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...
Macroglossia means an enlarged tongue. It may be absolute (greater than the 95th centile) or relative (enlarged compared with oral cavity).
Recognized associations include:
tends to be a relative macroglossia
may also have intermi...
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
The macula cribrosa is part of the vestibule of the inner ear, located medially between it and the lateral most part of the internal acoustic meatus. It represents clusters of small foramina that permit the passage of vestibular nerve fibers from the internal acoustic foramen into the vestibule....
Madelung disease, also known as Madelung-Launois-Bensaude syndrome or neck lipomatosis or multiple symmetric lipomatosis, is a rare benign entity clinically characterized by the presence of multiple and symmetric, non-encapsulated masses of fatty tissue, usually involving the neck and the upper ...
Mainzer-Saldino syndrome (also known as conorenal syndrome (CRS)) is a rare condition and is one of the ciliopathies. It is due to mutations in the IFT140 gene, whose protein product is one of the six parts of the intraflagellar transport complex A.
The syndrome's key characteristics are:
Major salivary gland cancer staging refers to TNM staging of malignant tumors of the major salivary glands (parotid, submandibular, and sublingual glands). In contrast, tumors arising from minor salivary glands are staged according to their site of origin. The following article reflects the 8th ...
The major salivary glands are the largest and most important of the salivary glands and comprise:
paired parotid glands
paired submandibular glands
paired sublingual glands
salivary gland tumors
Malignant mixed tumors of salivary glands, according to the WHO classification, comprise three tumors:
carcinoma ex pleomorphic adenoma
arises from pre-existing pleomorphic adenoma
carcinosarcoma (true mixed tumor of the salivary glands)
true malignant mixed tumor
99% also aris...
The malleus (plural: mallei) is the most lateral 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 p...
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, also known as the inferior alveolar canal (IAC), 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 o...
The mandibular foramen or inferior alveolar foramen is located on the medial surface of the ramus of the mandible and is the entrance to the mandibular canal. It transmits the inferior alveolar nerve, a branch of the posterior division of the mandibular division of the trigeminal nerve that supp...
The mandibular fossa or glenoid fossa is the smooth concave articular surface formed by both the squamous and petrous parts of the temporal bone. It forms the superior articular part of the 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 the mandible, which exposes it to high radiation. The maxilla can also be involved, but this is less frequent.
Mandibular ORN may occur in ...
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 multinodular goiter or nodular Graves disease 1.
The syndrome is rare with reported prevalence somewhere b...
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 categorizes 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 Martini glass sign describes the appearance of the globe in persistent hyperplastic primary vitreous (PHPV).
On MRI the retrolenticular tissue characteristic of this condition has a triangular shape, like that of a martini glass appearing as low T2 signal against the normal high T2 signal o...
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 masseter muscle is one of the muscles of mastication. It is rectangular shaped and consists of three layers of fibers, where the superficial layer is the largest.
origin: zygomatic arch
insertion: ramus and angle of mandible
innervation: masseteric nerve from the anterior divisio...
The masticator space is one of the 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 of deep...
Mastoid air cell opacification can occur in a number of situations and can include a spectrum of inflammatory, neoplastic, vascular, fibro-osseous, and traumatic changes.
The mastoid air cells (cellulae mastoideae) represent the pneumatization 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 i...
The mastoid antrum (or tympanic antrum) is an air space (up to 1 cm in size) lying posterior to the middle ear and connected to it by a short passageway, the aditus ad antrum. The superior wall or roof of the mastoid antrum is known as the tegmen mastoideum, which continues anteriorly as the teg...
The mastoid canaliculus (also known as Arnold's canal) arises from the pars vascularis of the foramen jugulare and runs to the mastoid segment of the facial nerve canal and contains Arnold nerve (auricular branch of vagus nerve).
History and etymology
Arnold's canal, and its corresponding ner...
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 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 pneumatized 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 tegmen ...
The maxillae (or maxillary bones) are a pair of symmetrical bones joined at the midline, which form the middle third of the face. Each maxilla 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 mo...
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 ostium or maxillary hiatus is an opening that forms the drainage channel of the maxillary sinus and is also one of the components of the ostiomeatal unit. It is located posteriorly and medially near the roof of the maxillary sinus measuring approximately 2-4 mm. It drains into the ...
The maxillary sinus (or antrum of Highmore) is a paired pyramid-shaped paranasal sinus within the maxillary bone which drains via the maxillary ostium into the infundibulum, then through hiatus semilunaris into the middle meatus. It is the largest of the paranasal sinuses.
Maxillary sinus carcinoma staging refers to TNM staging of epithelial malignancies involving the maxillary sinus. Applicable histologies include squamous cell carcinoma, adenocarcinoma, sinonasal undifferentiated carcinoma, and other rarer carcinomas. The following article reflects the 8th editi...
Maxillary tori are analogous to mandibular tori and are composed of densely mineralized 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 maxillary vein drains the pterygoid plexus and joins with the superficial temporal vein to form the retromandibular vein in the substance of the parotid gland 1.
The pterygoid plexus, and by extension, the maxillary vein helps to drain the areas supplied by the maxillary arte...
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 on a midsagittal section of CT or MRI that connects the anterior and posterior margins of the foramen magnum (basion to opisthion).
indicates the presence of basilar invagination (atlantoaxial impaction): the...
Meckel cave lesions are numerous. The aim of this article is to list them in an easy way for revision and assessment of differential diagnosis.
Meckel cave tumors account for only 0.5% of all intracranial tumors. The most common histologies include:
trigeminal schwannoma: most com...
Medial canal fibrosis is characterized 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.
a thickened tym...
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 and is attached to the medial aspect of the lateral pterygoid plate of the sphenoid...
The medial rectus muscle is one of the 6 extraocular 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 adductors...
A useful mnemonic to remember the bones forming the medial wall of the orbit is:
My Little Eye Sits (in the orbit); or
Medial Layer Eye Socket
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 into the chest and stomach or ascend to/into the head.
Vascular access devices
peripherally inserted central catheters (PICC)
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 cancer staging refers to TNM staging of medullary thyroid carcinomas. Papillary, follicular, and anaplastic thyroid carcinomas have similar TNM category definitions but different prognostic stage group definitions. The following article reflects the 8th edition manual published...
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 (see associations).
In non-familial case, it typically peaks in the 3rd to 4th decades.
Melanotic neuroectodermal tumor of infancy (MNTI) is a rare pigmented tumor that primarily affects the calvaria or facial skeleton of children, typically during infancy. It is usually a benign tumor, albeit locally aggressive.
Most cases are diagnosed during infancy, usually withi...
Melioidosis is an infectious disease caused by the bacterium Burkholderia pseudomallei (previously known as Pseudomonas pseudomallei) and is a multisystem disorder which may affect the lungs, brain, visceral organs, or musculoskeletal system.
Melioidosis is a disease of the monsoo...
Melkersson-Rosenthal syndrome (MRS), also known as cheilitis granulomatosa or Miescher-Melkersson-Rosenthal Syndrome, is a rare condition of unknown etiology characterized by:
granulomatous inflammation of the face and lips (non-caseating)
facial nerve (CN VII) paralysis (involvement of crania...
The membranous labyrinth or endolymphatic labyrinth is the part of the inner ear housed in the osseous labyrinth. It comprises 3 distinct, but joined, sensory sacs and ducts supplied by the vestibulocochlear nerve (CN VIII):
cochlear duct in the cochlea, responsible for hearing
utricle and sac...
Ménière disease (or idiopathic endolymphatic 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)
a sensation o...
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, typically adjacent to the root of the mandibular second premolar tooth. Normal variants have the forman located anywhere between the canine and 1st molar.
The mental nerve, a terminal branch of inferior alveolar nerv...
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 (plural: mesiodentes) 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 rati...
The mesotympanum (rare plural: mesotympana) forms the main compartment of the tympanic cavity and contains most of the important structures of the middle ear, including most of the ossicular chain.
The mesotympanum is found in the middle ear.
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 chronic 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 metopic suture (also known as the frontal, interfrontal, or 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, a...
MIBG scan is a scintigraphic study that uses metaiodobenzylguanidine labeled to iodine-123 or iodine-131. It is indicated in the investigation of pheochromocytoma.
MIBG is positive in:
olfactory neuroblastoma 1
carcinoid tumor 4
Michel aplasia, also known as complete labyrinthine aplasia (CLA), is a congenital abnormality of the inner ear and is characterized by bilateral absence of differentiated inner ear structures with resultant anacusis. It should not be confused with Michel dysplasia.
Michel aplasia i...
Microdontia is where a tooth appears smaller than normal. It most commonly affects the maxillary lateral incisor and the third molars.
Microgenia is a term meaning a small chin. It is somewhat related to but distinct from the term micrognathia which means a small mandible.
Microgenia can be isolated or be associated with a number of anomalies which include
campomelic dysplasia 1
The term micrognathia describes a small mandible.
A small mandible occurs secondary to abnormalities of the first branchial arch which in turn are caused by deficient or insufficient migration of neural crest cells and usually occur around the 4th week of gestation.
Microphthalmia essentially means small eyes. It is characterized 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 recognized 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 middle ear cavity, also known as tympanic cavity or tympanum (plural: tympanums/tympana), is an air-filled chamber in the petrous part of the temporal bone. It is separated from the external ear by the tympanic membrane, and from the inner ear by the medial wall of the tympanic...
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 etiology, with resorption of air and extravasat...
Development of granulation tissue in the middle ear cavity is a generalized 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 tiny articulating bones in the middle ear known as 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 i...