Jod-Basedow phenomenon is hyperthyroidism following iodine intake in a person with long term underlying thyroid disease.
Jod-Basedow phenomenon occurs due to either overactivation of the entire thyroid gland or, more commonly, autonomous nodules within the gland after iodine repletio...
Jugular bulb diverticulum refers to a protrusion of the jugular bulb with waist-like margin, which can occur with or without jugular bulb dehiscence.
The prevalence on imaging series ranges 1-8% 1,2.
Many patients are asymptomatic, but jugular bulb diverti...
The jugular foramen courses anteriorly, laterally, and inferiorly as it insinuates itself between the petrous temporal bone and the occipital bone.
The jugular foramen is usually described as being divided into two parts by a fibrous or bony septum, called the jugular spine, into...
Jugular foramen schwannomas are a rare type of intracranial schwannoma that presents as a jugular fossa mass involving the jugular foramen.
In those without neurofibromatosis type 2 (NF2), they tend to present between the 3rd to 6th decades of life. There is a recognized female pr...
The jugular fossa is a depression situated on the inferior surface of petrous temporal bone posterior to the inferior opening of carotid canal. It lodges the jugular bulb. Anteriorly, lies the jugular foramen.
glomus jugulare is the most common tumor of jugular fossa
Jugular fossa masses comprise a range of pathological lesions that arise from or extend into the jugular fossa in the skull base. Although not a common location for tumors it is not unusual for jugular fossa lesions to be discovered incidentally on cross-sectional imaging.
The jugular spine is a small sharp bony ledge which separates the two parts of the jugular foramen - pars nervosa anteromedially and pars vascularis posterlaterally. It is an important landmark, as masses of the jugular foramen (e.g. glomus jugulare) may erode the jugular spine, helping distingu...
The jugular trunks are small short paired lymphatic trunks, each one draining one side of the head and neck, forming an important terminal part of the lymphatic system 1-3.
the left and right jugular trunks are found in the root of the neck
the organs of the he...
The jugulodigastric lymph nodes, also known as subdigastric lymph nodes, are deep cervical nodes located below the posterior belly of the digastric muscle and anterior to the internal jugular vein.
They are located in neck node level IIa and receive lymphatic drainage from the tonsils, pharynx,...
Juvenile nasopharyngeal angiofibromas (JNA) are a rare benign, but locally aggressive, vascular tumor.
Juvenile nasopharyngeal angiofibromas occur almost exclusively in males and usually in adolescence (~15 years). They account for only 0.5% of all head and neck tumors 2, but are ...
Staging of juvenile nasopharyngeal angiofibromas is performed with cross-sectional imaging and relies on the identification of local tumor extent, and invasion of adjacent spaces. For a discussion of this entity please refer to the parent article: juvenile nasopharyngeal angiofibroma.
Kartagener syndrome (also known as Kartagener-Afzelius syndrome) is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterized by abnormal ciliary structure or function, leading to impaired mucociliary clearance.
The prevalence of primary ciliary dyski...
Kayser-Fleischer rings, sometimes shortened to K-F rings, are caused by copper deposition in the cornea and are a specific, clinical sign of Wilson disease.
They are usually brown or dark reddish in color. Early on they may need a slit lamp to be visible before they becom...
Keratosis obturans is a rare external auditory canal (EAC) disease characterized by abnormal accumulation and consequently occlusion and expansion of the bony portion of the EAC by a plug of desquamated keratin. It can be confused for EAC cholesteatoma but they are completely different entities ...
The Keros classification is a method of classifying the depth of the olfactory fossa.
The ethmoid labyrinth is covered by the fovea ethmoidalis of the frontal bone and separates the ethmoidal cells from the anterior cranial fossa.
The very thin, horizontal cribriform plate (lamina cribrosa) of...
Kiesselbach plexus (Kiesselbach area or Little's area) is a vascular region of the anteroinferior nasal septum that comprises four arterial anastomoses:
anterior ethmoidal artery
a branch of the ophthalmic artery
a branch of the maxillary artery
greater palatine artery...
The Killian dehiscence is a triangular-shaped area of weakness in the muscular wall of the pharynx, between the transverse and oblique bundles of the inferior pharyngeal constrictor 1.
It is located in the posterior wall of the laryngopharynx, slightly above the origin of the eso...
Kimura disease, also known as eosinophilic hyperplastic lymphogranuloma, is a rare benign inflammatory disease that characteristically manifests as enlargement of cervical lymph nodes and salivary glands.
Kimura disease typically affects males (80%) between 20 and 40 years of age ...
The term kissing carotids refers to tortuous and elongated vessels which touch in the midline. They can be found in:
within the pituitary fossa
within sphenoid sinuses
within sphenoid bones
The significance of kissing carotids is two-fold:
may mimic intrase...
Klaus height index is the distance between tip of the dens and the tuberculum torcula line (Twining's line) 1,2. A normal height is 40-41 mm.
A decreased Klaus height index is seen in basilar invagination.
The Koerner septum is a thin bridge of bone which divides the petrous and squamous portion of the mastoid air cells at the level of the mastoid antrum. It is commonly eroded by middle ear cholesteatomas.
K-TIRADS is a reporting system designed by the Korean Society of Thyroid Radiology for ultrasound assessment of thyroid nodules and stratification of the requirement for FNA and malignancy. There is also stratification of indications for lymph node sampling.
This is a five-stage system using de...
Kuhn classification is an anatomical classification for the subtypes of frontal cells.
type 1 (~37%): a single air cell above the agger nasi cell
type 2 (~19%): two or more air cells above the agger nasi cell
type 3 (~7%): a single large cell above the agger nasi cell that extends into the fr...
Küttner tumor (KT) refers to a chronic sclerosing sialadenitis. Despite the term tumor, it is a non neoplastic condition. It is classically described in relation to the submandibular gland but less commonly can also affect the other salivary glands 9 and occasionally also the lacrimal gland 6.
This article lists a series of labeled imaging anatomy cases by system and modality.
CT head: non-contrast axial
CT head: non-contrast coronal
CT head: non-contrast sagittal
CT head: angiogram axial
CT head: angiogram coronal
CT head: angiogram sagittal
CT head: venogram axial
The labyrinth can refer to:
labyrinth of the inner ear
labyrinth of the ethmoid bone
The labyrinthine artery, also known as the auditory artery or internal auditory artery, is a long and slender artery that is the main arterial supply to the vestibular apparatus and cochlea. It also vascularizes the VII and VIII cranial nerves.
It usually originates from the AICA (~85%), althou...
Labyrinthitis is inflammation of the membranous labyrinth.
Labyrinthitis can be divided according to etiology.
Labyrinthitis is a potential complication of acute otomastoiditis with the spread of infection or of toxins from the middle ear to the inner ear via either th...
Labyrinthitis ossificans, also known as labyrinthine ossification, represents pathological ossification of the membranous labyrinth as a response to an insult to the inner ear.
It is usually associated with profound sensorineural hearing loss, and may sometimes be associa...
The labyrinth or lateral mass of the ethmoid bone consists of a number of thin-walled cellular cavities, the ethmoidal air cells, arranged in two groups: anterior and posterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial, part of the...
The labyrinth of the inner ear is the combined sensory organ of hearing and balance and its surrounding bony cavity located in the petrous temporal bone, consisting of two components:
the osseous labyrinth, the bony cavity, which houses
the membranous labyrinth, a tubular sac filled with endol...
The lacrimal apparatus consists of the lacrimal gland and the nasolacrimal drainage apparatus.
The gland produces tears secreted into the lateral aspect of the superior fornix. The serous fluid washes over the eye and is drained at the medial canthus by the superior and inferior lacrimal canal...
The lacrimal artery is a branch of the ophthalmic artery that supplies the lacrimal gland.
The lacrimal artery travels along the upper border of the lateral rectus muscle with the lacrimal nerve to supply the lacrimal gland as well as the eyelids and conjunctiva.
The lacrimal bones are paired craniofacial bones forming anterior aspect of the medial orbital walls.
The lacrimal bones have two surfaces and four borders. The lateral orbital surface is divided by a vertical posterior lacrimal crest with an anterior fossa for lacrimal sac and ...
The lacrimal canaliculi form the first part of the nasolacrimal drainage apparatus that drains tears produced by the lacrimal gland.
There are two lacrimal canaliculi - superior and inferior on each side. They commence at the superior and inferior lacrimal puncta, which drain te...
The lacrimal gland lies in the superolateral aspect of the orbit. It is part of the lacrimal apparatus and is responsible for tear production.
The lacrimal gland is roughly almond-sized and located anteriorly in the superolateral aspect of the extraconal space of the orbit. It h...
Lacrimal gland masses can be classified into two broad groups - inflammatory (~50%) and neoplastic, either lymphoma (25%) or salivary gland type tumors (~25%).
affects ~25% of patients with systemic disease
orbital inflammatory pseudotumor
The lacrimal nerve is the smallest branch of the ophthalmic division of the trigeminal nerve (V1).
The lacrimal nerve divides off the ophthalmic division of the trigeminal nerve (V1) just before entering the orbit through the superior orbital fissure outside and superolateral to ...
The lacrimal (or nasolacrimal) sac forms part of the nasolacrimal drainage apparatus. It is located in the preseptal part of the orbit.
The lacrimal sac lies in the lacrimal fossa on the inferomedial aspect of the bony orbit between the posterior and anterior lacrimal crests. It...
The lacrimal sac fossa is an excavated fossa in the inferior aspect of the anteromedial orbital wall which contains the lacrimal sac. It is bounded by the anterior and posterior lacrimal crests of the maxillary and lacrimal bones, respectively. In adults, it measures approximately 8-9 mm anterop...
Lacrimal sac masses are very uncommon and more commonly have a malignant (~80%) rather than benign (~20%) etiology.
granulomatosis with polyangiitis
The lacrimomaxillary suture is a syndesmotic suture between frontal process of the maxilla and lacrimal bone in inferior aspect of anteromedial wall of the orbit approximately half way between the anterior and posterior lacrimal crests. It corresponds, internally, to the maxillary line in later...
Lagophthalmos refers to the inability of an individual to completely close the eyelids and can result in drying of the eyes and irritation, and even permanent damage.
most common in facial nerve palsies (e.g. Bell palsy)
trauma/surgery: scarring of the eyelids 1 (cicatric...
The lambda is the midline bony landmark where the lambdoid sutures and sagittal suture meet, between the occipital and two parietal bones. It may be a depression and therefore palpable. Accessory occiptal bones are common near the lambda, usually associated with the lambdoid sutures.
It is the ...
The lamdboid suture is the junction between the superior border of the occipital bone and the posterior borders of the right and left parietal bones. It normally fuses at approximately 26 years of age.
The term lamellated (or laminated which means the same thing) is a radiopathological term used to describe the layered appearance of many calculi, including those of the renal tract, the salivary glands, and the biliary tree. The internal structure of these calculi has been likened to that of an...
The lamina papyracea, also known as the orbital lamina of the ethmoid bone, is the principal component of the medial wall of the orbit, and also the lateral surface of the ethmoid air cells.
superiorly with the orbital plate of the frontal bone
inferiorly with t...
Dehiscence of the lamina papyracea is an anomaly of the paranasal sinuses represented by a defect of the medial orbital wall. It is thought to be a benign congenital variant of no clinical significance.
Almost all patient tend to be asymptomatic, according to one study 2....
Large vestibular aqueduct syndrome (LVAS), also known as large endolymphatic sac anomaly (LESA), refers to the presence of congenital sensorineural hearing loss with an enlarged vestibular aqueduct due to enlargement of the endolymphatic duct. It is thought to be one of the most common congenita...
Laryngeal carcinoma staging refers to TNM staging of carcinomas involving the supraglottic, glottic, and subglottic larynx. The vast majority of applicable cases are squamous cell carcinomas, but other epithelial tumors are also included. The following article reflects the 8th edition published ...
The laryngeal cartilages form the "skeleton" of the larynx. There are three unpaired (midline) and three paired cartilages:
Laryngeal cysts can occur in any part of the larynx, but are more frequent in supraglottic locations, such as the epiglottis and vallecula. The prevalence of each location varies on different studies.
The laryngeal cysts represent a rare group, about 5%, of benign laryngeal lesio...
The laryngeal saccule is a mucosa-lined pouch that arises from the anterior aspect of the roof of the laryngeal ventricle. It is most prominent in newborns but involutes during childhood.
medial: false vocal cords
lateral: thyroid cartilage
Dilatation of the lary...
Laryngeal trauma is uncommon in the setting of external blunt or penetrating trauma. The larynx may also be injured internally, for example during endotracheal intubation.
Symptoms include hoarseness, laryngeal pain, dyspnea, and/or dysphagia. Also, stridor, hemoptysis, s...
The laryngeal ventricle is a slitlike, mucosa-lined, space located between the true and false vocal cords. It is often seen on lateral radiographs of the neck as an air-filled space between the true and false vocal cords. It should not be confused with the laryngeal vestibule.
The laryngeal vestibule is the part of the laryngeal cavity lying between the laryngeal inlet and vocal folds.
It is found within the supraglottis. It has a wedge-shaped cross-section, its base lying anteriorly, with its apex tapering posteriorly.
anterior: tubercle ...
Laryngocele refers to dilatation of the saccule of the laryngeal ventricle and is unilateral in the vast majority of cases 8.
On imaging, these lesions are generally characterized as well-defined, thin-walled, fluid or air-filled cystic lesions in the paraglottic space. The communication with t...
The larynx is an inferior continuation of the oropharynx. It extends from the epiglottis (namely the glossoepiglottic and pharyngoepiglottic folds) to the inferior aspect of the cricoid cartilage. Inferiorly, it continues as the cervical trachea.
The larynx consists of a cartila...
The lateralized internal carotid artery is an anatomic variation of the course of the petrous segment of the internal carotid artery (ICA). It can be visualized on CT by its more posterolateral entrance to the skull base and protrusion into the anterior mesotympanum.
The lateral lamella is the name given to the lateral boundary of the cribriform plate. It runs vertically and joins the fovea ethmoidalis inferomedially. It is the thinnest part of the cribriform plate.
The lateral lamella needs to be assessed on pre-functional endoscopic sinu...
The lateral posterior inferior nasal nerve is a branch of the greater palatine nerve that supplies the posteroinferior nasal lateral wall.
The nerve branches off the greater palatine nerve in the greater palatine canal and exits the canal though a tiny un-named foramen in the pal...
The lateral pterygoid muscle, also known as pterygoideus externus or external pterygoid muscle, is one of the muscles of mastication.
The lateral pterygoid is a short, thick muscle, somewhat conical in form, which extends almost horizontally, posteriorly and laterally between th...
The lateral pterygoid nerves or nerves to lateral pterygoid muscle are a pair of motor branches of the anterior division of the mandibular division of the trigeminal nerve.
The two nerves divide off the anterior division and course along side the buccal nerve. Each nerve then pie...
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 (also known as postanginal septicemia) 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.
Lenticonus is a rare congenital abnormality characterized by conical bulging of the posterior or anterior lens surface. If the bulging is global rather than conical, the condition is referred to as lentiglobus 1.
It produces a decrease in visual acuity and irregular refra...
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 claviculae or cleidocervical muscle is an uncommon accessory muscle in the neck that may be mistaken for a neck mass.
origin: transverse process of upper cervical vertebra
insertion: middle or lateral third of the clavicle
innervation: branches of the cervical plexus
The levator glandulae thyroideae muscle (a.k.a. musculus levator glandulae thyroideae or levator glandulae thyroideae of Soemmerring) is an anatomic variant, consisting of a band of fibrous/fibromuscular tissue, connecting the pyramidal lobe of the thyroid to the hyoid bone. When muscle fibers a...
Levator labii superioris alaeque nasalis (LLSAN) muscle is traditionally thought of as a muscle of the mouth, but is also a crucial muscle of the nose, a subset of the muscles of facial expression 1.
origin: maxilla, nasal bone, medial canthus
insertion: nasal base
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 extraocular muscles; it does not insert on the globe and therefore does not produce eye movements. It is composed of skeletal muscle but on its under...
The levator veli palatini muscle 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 two sites of origin:
inferior surface of petrous temporal bone
medial rim of the audito...
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 supplying sensation (both gustatory (taste) and non-gustatory) to the anterior two-thirds of the tongue.
The lingual nerve divides off the posterior division and des...
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-...
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...