The lateral rectus muscle is one of the 6 extraocular muscles that control eye movements. It is responsible for abduction and is the only muscle that is innervated by the abducens nerve (CN VI). It should normally measure 2.9 ± 0.6 mm.
innervation: abducens nerve (CN VI)
A mnemonic for the layers of the scalp is:
This is particularly helpful when considering the location of a scalp hematoma.
C: connective tissue
A: (galea) aponeurosis
L: loose connective tissue
Le Fort fractures are fractures of the midface, which collectively involve separation of all or a portion of the midface from the skull base. In order to be separated from the skull base, the pterygoid plates of the sphenoid bone need to be involved as these connect the midface to the sphenoid b...
Leiomyosarcomas (LMS) are extremely rare malignant neoplasms that originate from smooth muscle cells and may be considered the malignant counterpart of a leiomyoma. They are classified as a soft tissue tumor and account for ~8% of malignant soft tissue tumors 10.
Lemierre syndrome refers to thrombophlebitis of the internal jugular vein(s) with distant metastatic sepsis in the setting of initial oropharyngeal infection such as pharyngitis/tonsillitis with or without peritonsillar or retropharyngeal abscess.
Since the advent of antibiotics, ...
The lentiform nodule (also known as the lenticular process) is the inferior most part of the incus which articulates with the head of the stapes.
Lentigo maligna, also known as Hutchinson freckle, is a non-familial precursor to lentigo maligna melanoma, which accounts for 5-15% of cases of malignant melanoma. It is most frequent in the head and neck.
It should not be confused with numerous other Hutchinson named entities including:
Leontiasis ossea is largely a historical term used to describe a number of conditions that result in the affected patient's face resembling that of a lion. Although it is most frequently associated with craniofacial fibrous dysplasia, it has a broader meaning encompassing other lesions that have...
Leptomeningeal cysts, also known as growing skull fractures, are an enlarging skull fracture that occurs near post-traumatic encephalomalacia. The term cyst is actually a misnomer, as it is not a cyst, but an extension of the encephalomalacia. Hence, it is usually seen a few months post-trauma.
The lesser occipital nerve, also known as the small occipital nerve, is a cutaneous branch of the cervical plexus that innervates the skin of the neck and scalp posterior and superior to the auricle.
The lesser occipital nerve arises from the ventral ramus of C2, although...
The lesser palatine foramina are 2 small foramina representing the openings in the hard palate of the lesser palatine canal (which is a small accessory canal arising form the greater palatine canal). They are located in the posterior palatine bone posterior to the greater palatine foramen and po...
The lesser palatine nerves (or posterior palatine nerves) are a group of 2 to 3 nerves (usually 2 nerves) that arise of the maxillary division of the trigeminal nerve and contributes to the pterygopalatine ganglion.
The lesser palatine nerves divide off the maxillary division jus...
The lesser petrosal nerve carries parasympathetic (secretory) fibers from both the tympanic plexus and the nervus intermedius, to the parotid gland. The tympanic plexus arises from glossopharyngeal nerve (CN IX) via Jacobson's nerve.
The lesser petrosal nerve originates at the geniculate gangli...
The lesser wing of the sphenoid bone, or orbito-sphenoid, is a sharp, pointed triangular plate arising laterally from the upper anterior portion of the sphenoid body.
The lesser wing features both superior and inferior surfaces:
the superior surface is flattened and is in conta...
Leukocoria (also spelled as leucocoria or leukokoria) refers to an abnormal white reflection from the retina of the eye. Despite its color, the reflection is related to the familiar red-eye effect. Usually, when a light is shone through the iris, the retina appears red to the observer. In leukoc...
The levator palpebrae superioris muscle is a small muscle of the superior orbit that elevates and retracts the upper eyelid. It is not part of the extra-ocular muscles; it does not insert on the globe and therefore does not produce eye movements. It is mostly composed of skeletal muscle but ther...
The levator veli palatini is one of the 5 paired muscles of the soft palate. It is a cylindrical muscle which together form a V-shaped sling behind and above the soft palate.
origin: it has 2 sites of origin:
inferior surface of petrous temporal bone
medial rim of the auditory tube
The Lillie-Crowe sign is used in the diagnosis of unilateral sinus thrombophlebitis. Digital compression of the opposite internal jugular vein causes dilatation of the retinal veins.
Linear scleroderma, also known as scleroderma en coup de saber, is a very focal form of scleroderma classically characterized by a linear band of atrophy involving the frontal or frontoparietal scalp and subjacent thinned calvaria associated with ipsilateral focal brain abnormalities.
In the b...
The lingual artery is one of the branches of the external carotid artery and supplies the oral floor and tongue.
origin: branch of the external carotid artery at the level of the C3
course: towards hyoid bone, then loops down towards the tongue
supply: oral floor and tongue
The lingual nerve is a sensory branch of the posterior division of the mandibular division of the trigeminal nerve.
The lingual nerve divides off the posterior division and descends anterior to the inferior alveolar nerve to course between the lateral pterygoid and tensor veli pa...
A lingual thyroid is a specific type of ectopic thyroid and results from the lack of normal caudal migration of the thyroid gland.
NB: Location at the base of the tongue aside, the information in this article can relate to any ectopic thyroid tissue.
The condition is congenital a...
The lingual tonsils are aggregations of lymphoid follicles that mediate B- and T-cell lymphocytes, which serve a role in formulating the immune system. They are covered by stratified squamous nonkeratinized epithelium and contain deep crypts and mucosal glands. They form a part of the Waldeyer r...
The lingual vein is formed by the sublingual, deep lingual, and dorsal lingual veins 1. It is a paired vein draining the tongue.
The lingual veins accompany the lingual artery between the hyoglossus and genioglossus and enters the internal jugular vein near the greater horn of th...
Lingula (plural lingulae) can refer to a number of different anatomical structures:
lingula (sphenoid bone)
History and etymology
Lingula is the diminutive form of lingua, Latin for the tongue. Thus lingula is used for a small tongue-l...
The lingula of the mandible (also known as Spix spine) is a triangular bony projection or ridge on the medial surface of the ramus of the mandible, immediately superior to the mandibular foramen. It provides attachment for the sphenomandibular ligament 1,2.
History and etymology
Lipoedematous scalp is a rare condition characterized by the accumulation of fatty tissue in the subcutaneous layer of the scalp, resulting in soft enlargement of the head. If it is associated with loss of hair then the term lipoedmeatous alopecia is used.
Histology demonstrates inc...
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 a condition that can occur as a result of a stroke involving the brainstem; the stroke damages the ventral brainstem, corresponding to the pyramidal bundles.
The infarct is pontine; the midbrain is preserved. The oculomotor nerve III is intact so the...
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 suggests underlying necrosis and can be seen in:
metastatic carcinoma (or lymphoma)
infections (tuberculous or fungal)
inflammatory necrotic disorders (e.g. Kikuchi-Fujimoto disease)
extra adrenal myelolipoma
Ludwig angina refers to rapidly progressive inflammation (cellulitis) 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; ...
Lymph nodes in the neck have been historically divided into seven anatomic 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 accepted and radiologically useful definitions.
Level I: su...
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
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 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 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 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 dee...
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 tegment...
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 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 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 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...
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 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 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)
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.
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 (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...