Dacryocystitis is the inflammation of the nasolacrimal sac related to impairment in the lacrimal drainage system and superimposed infection.
Dacryocystitis has a bimodal distribution: neonates due to congenital abnormalities and, when acquired, usually affect individuals older th...
Dacryocystoceles are caused by obstruction of both the proximal and distal ends of the nasolacrimal duct. An imperforate Hasner membrane causes the distal blockage, but the cause of proximal obstruction is less clearly understood.
Dacryocystoceles, although rare, are the second mo...
Dacryocystography (DCG) is a fluoroscopic contrast examination of the nasolacrimal apparatus. The nasolacrimal duct is cannulated enabling iodinated contrast to be instilled into the nasolacrimal system.
The most frequent indication is epiphora: excessive tearing or watering of the...
The danger space is a potential space located behind the true retropharyngeal space, which connects the deep cervical spaces to the mediastinum.
anteriorly: alar fascia
posteriorly: prevertebral layer of the deep cervical fascia
Deafness (also known as hearing loss or impairment) is the partial or complete loss of the sense of hearing.
It may be subdivided etiologically into
conductive: impairment of the passage of sound waves from the auricle to the inner ear
sensorineural: impairment localizes to the inner ear, in...
The deep auricular artery is the first named branch of the maxillary artery and passes through the bony or cartilaginous wall of the external acoustic meatus to supply the skin of that canal and part of the tympanic membrane. It can sometimes contribute a small branch to the arterial supply of t...
Deep brain ultrasound (DBUS) therapy is a form of precision medicine using a technique based on the principle of high-intensity focused ultrasound (HIFU), also referred to as focused ultrasound surgery (FUS).
The method combines two main components 1:
MRI of the ...
The deep cervical fascia consists of 3 separate but related fascial layers that encircle structures in the neck and allow anatomic compartmentalisation. These layers cannot be visualized directly by cross sectional imaging. All 3 layers meet to form the carotid sheath. From superficial to deep, ...
The deep petrosal nerve transmits post-ganglionic sympathetic fibers from the internal carotid plexus to the Vidian nerve on its way to the pterygopalatine ganglion.
The nerve begins at the internal carotid plexus and runs alongside the lateral aspect of the internal carotid arte...
Head and neck anatomy is described in slightly different terms in the radiology literature reflecting the importance of fascia lined spaces in confining various pathologies. As such the neck has been divided into a number of 'deep spaces' which overlap with traditional anatomical description.
The deep temporal arteries (anterior, middle and posterior) are branches from the second part of the maxillary artery. They ascend between the temporalis muscle and the pericranium supplying the overlying muscle.
The anterior branch communicates with the lacrimal artery by means of small branch...
The deep temporal nerves are a pair of motor branches of the anterior division of the mandibular division of the trigeminal nerve. It should not be confused with the temporal branch of the facial nerve.
The two deep temporal nerves divide off the anterior division and course abov...
Dehiscence is a general term referring to 'splitting open' and is used in a variety of contexts in medicine generally and radiology more specifically.
The two most common usages are:
splitting open of a wound (e.g. sternal dehiscence)
loss of bone separating one structure from another (e.g. ...
Dehiscent jugular bulbs are present when the sigmoid plate between a high riding jugular bulb and the middle ear is absent, allowing the wall of the jugular bulb to bulge into the middle ear cavity.
The estimated incidence is ~5% (range 3.5-7%) of the symptomatic population (e.g. ...
The Delphian (prelaryngeal/precricoid) node is one of the cervical lymph node groups that comprise level VI cervical lymph nodes and is not routinely excised in radical neck dissections.
It is located between the cricothyroid muscles, above the thyroid isthmus, lying directly ant...
Dental (periapical) abscess is an acute infection of the periapical tissue around the root of the tooth.
Patients may present with pain, edema, and purulent discharge localized to the site of pathology with or without fever and tender cervical lymphadenopathy 1.
Dental caries are cavities in teeth ('caries' is both the singular and plural form). They are very common and can lead to serious morbidity.
Focal enamel and dentin demineralization result in cavity formation. There are multiple theories for their pathogenesis but contributing facto...
Dentigerous cysts, also called follicular cysts, are slow growing benign and non-inflammatory odontogenic cysts that are thought to be developmental in origin.
On imaging, they usually present as a well-defined and unilocular radiolucency surrounding the crown of an unerupted or impacted tooth ...
The Denver criteria are a set of screening criteria for blunt cerebrovascular injury (BCVI) in trauma used to reduce the need for CT angiography and its associated radiation exposure.
The screening protocol criteria 1,3 for BCVI are divided into signs and symptoms of BCVI a...
Depressed skull fractures result in the bone of the skull vault being folded (depressed) inward into the cerebral parenchyma. It is usually the result of a high energy impact to the skull.
These mostly (~75%) occur in the frontoparietal region 3.
There are number of as...
The depressor anguli oris (triangularis) muscle is one of the muscles of facial expression.
origin: oblique line of the mandible
angle of the mouth
superficial fibers from both sides merge to form the transversus menti
innervation: facial nerve
De Quervain thyroiditis, or subacute granulomatous thyroiditis, is a form of self-limited subacute thyroiditis usually preceded by an upper respiratory tract viral infection such as mumps, measles, coxsackie virus, adenovirus, and influenza viruses.
It usually affects middle-age f...
The dermolipoma is one of the fat-containing epibulbar mass lesions of lateral canthal area beneath the temporal or superotemporal bulbar conjunctivae.
Dermolipomas are congenital and more commonly seen in young patients with mean age of 30 years old. There is no gender predilect...
Descending necrotizing mediastinitis is a severe form of mediastinitis and refers to an acute, polymicrobial infection of the mediastinum that usually spreads downwards from oropharyngeal, cervical, and odontogenic infection.
diabetes: more than one-third of patients...
Developmental orbital cysts correspond to a heterogeneous group of congenital orbital developmental anomalies with cystic component, ranging from closed sacs lined by an ectodermal epithelium, such as epidermoid and dermoid, to neoplasms as teratoma 1.
choristoma: it is formed by heterotopic...
A deviated nasal septum is a common incidental finding seen on brain and paranasal sinus CT studies.
It can be congenital or acquired. The most common acquired cause is trauma from motor vehicle collisions, sports-related injuries, and altercations.
Diabetes insipidus (DI) is the deficiency or resistance to the hormone vasopressin (antidiuretic hormone), which results in polyuria and polydipsia.
DI occurs in 3 per 100,000 people 2.
DI may be described as 1-3:
central/neurogenic/hypothalamic: vasopressin deficie...
Differential diagnosis for calcified masses in the mandible includes:
calcifying odontogenic cyst (Gorlin cyst)
calcifying epithelial odontogenic tumor (Pindborg tumor)
The digastric line, also known as the biventer line, has been described and used to evaluate basilar invagination on frontal skull plain film and coronal CT images.
The digastric line is drawn between right and left digastric grooves, which are located medial to the mastoid apices. These are co...
The digastric muscle is composed of two bellies, anterior and posterior, connected by an intermediate round tendon. The two bellies of the muscle have different embryonic origins and hence are supplied by different cranial nerves.
anterior belly: digastric fossa on the deep sur...
The digastric triangle is one of the paired triangles in the anterior triangle of the neck. The triangles of the neck are surgically focused, first described from early dissection-based anatomical studies which predated cross-sectional anatomical description based on imaging (see deep spaces of ...
Dilator naris forms the alar component of nasalis muscle, and is one of the muscles of the nose, a subset of the muscles of facial expression.
insertion: nasal ala
innervation: facial nerve (VII)
action: flaring of the nostril
Dolan's lines are the collective name given to three lines described by Dolan and Jacoby 1 that aid in evaluating for maxillofacial fractures on an occipitomental skull radiograph. They are usually used as an adjunct to McGrigor-Campbell lines.
orbital line traces the inner margins of the later...
The term dolichoectasia means dilated and elongated. It is used to characterize arteries that have shown a significant deterioration of their tunica intima (and occasionally the tunica media), weakening the vessel walls and causing the artery to elongate and distend.
Dorello canal channels the abducens nerve (CN VI) from the pontine cistern to the cavernous sinus.
Dorello canal is found at the medial most end of the petrous ridge at the confluence of the inferior petrosal, basal, and cavernous sinuses.
The dorsal nasal artery, also known as the dorsonasal artery, is a terminal branch of the ophthalmic artery.
Arising as a terminal branch of the ophthalmic artery, the dorsal nasal artery exits the orbit after piercing the orbital septum above the medial canthal tendon (medial pa...
The dorsum sellae is the square shaped process of the sphenoid bone. It ascends superiorly from the posterior part of the sphenoid body to form the posterior wall of the sella turcica.
The dorsum sellae forms the posterior wall of the sella turcica, which houses the pi...
Thickening of the insertion of the lateral pterygoid muscle can mimic an anterior displaced temporomandibular disc. When both thickening of the inferior belly insertion and an anteriorly displaced disc are present, the two structures parallel each other; the so-called "double disc" sign.
The duct of Rivinus connects the sublingual gland to the floor of the mouth.
Despite its name, it is not a single duct, but numerous small ducts all of which open into the floor of the mouth and are collectively termed the duct of Rivinus.
The largest of these little ductules is the major duct...
The ducts of the salivary glands allow the passage of salivary juice from the glands to the oral cavity:
parotid duct (Stenson duct): connects the parotid gland to the buccal mucosa, adjacent to maxillary second molar
submandibular duct (Wharton duct): connects the submandibular gland to the f...
A useful mnemonic to remember differential diagnoses associated with a dural tail sign is:
My Scary Dog Likes To Stand Guard
D: dural metastases
Dysphagia refers to subjective awareness of difficulty or obstruction during swallowing. It is a relatively common and increasingly prevalent clinical problem. Odynophagia is the medial term for painful swallowing.
Fluoroscopy is the mainstay of imaging assessment but manometry can help evaluat...
Eagle syndrome refers to symptomatic elongation of the styloid process or calcified stylohyoid ligament 1,2. It is often bilateral. In most cases, the cause is unknown; however, the condition is sometimes associated with disorders causing heterotopic calcification such as abnormal calcium/phosph...
The ear refers to the entire vestibulocochlear organ and is divided anatomically into:
Epstein-Barr virus-associated smooth muscle tumors (EBV-SMT) are rare and encountered in immunocompromised individuals.
These tumors are generally exceedingly rare, and only seen with any frequency in the setting of immunosuppression, particularly in HIV/AIDS patients, but also po...
Ectodermal dysplasia (ED) refers to a heterogeneous group of genetic disorders that cause abnormal ectoderm development. The effect is a non-progressive defect in the development of two or more tissues derived from embryonic ectoderm.
ED is rare with an estimated prevalence of 1:...
Ectopia lentis refers to subluxation or dislocation of the lens of the eye secondary to dysfunction or disruption of zonular fibers.
systemic and syndromic disorders
typically upwards and out
most common spontaneous cause 2
homocystinuria - typ...
An ectopic thyroid gland is one which is located in a location other than the normal position anterior to the laryngeal cartilages.
During embryological development, the thyroid gland migrates down from the foramen cecum at the posterior aspect of the tongue to its permanent lo...
Edentulism (or edentulousness) means absence of dentition and can have a significant impact on a patient's quality of life in addition to the negative cosmetic effects.
When edentulism is used as a standalone term it usually means that all the teeth are absent, i.e. complete edentu...
Emissary veins (also known as the vena emissaria) are the small valveless veins that pass via the foramina of the skull, providing a venous communication between the dural venous sinuses and veins of the scalp or veins inferior to the skull base.
Named emissary veins
condylar emissary vein
Endolymph is one of the two types of cochlear fluids, the other being perilymph. It is located in the scala media of the cochlea.
It is secreted by the stria vascularis (colloquially called 'battery of the cochlea') on the outer wall of the scala media. It has a high level of potassium (K+) and...
The endolymphatic duct is a small epithelial-lined channel, part of the membranous labyrinth that passes through the vestibular aqueduct in the bony labyrinth of the petrous temporal bone. It arises from the utricle and saccule via the utriculosaccule duct and drains endolymph. The distal end is...
Endolymphatic sac tumors (ELSTs) are very rare, locally invasive tumors of endolymphatic sac. Early detection of these tumors is critical, because early surgical intervention may prevent further hearing loss. Endolymphatic sac tumors do not metastasize but are highly locally aggressive.
Endophthalmitis is a potentially sight-threatening condition that involves intraocular inflammation of any cause. It is distinguished from panopthalmitis in that is does not extend beyond the sclera. It is either infectious or noninfectious in etiology, but in clinical practice, intraocular infe...
There is a short list of causes for enlarged extraocular muscles:
thyroid associated orbitopathy
amyloidosis (very rare) 2
Enophthalmos refers to the posterior displacement of the globe in the orbit. It implies that the globe itself is normal and is caused by either one or a combination of 1:
structural alterations in the bony orbit
orbital fat atrophy
Specific causes include 2:
orbital blowout fract...
The epiglottis is a leaf-shaped fibrocartilaginous structure that forms part of the supraglottic larynx and defines the division of the hypopharynx from the larynx.
The epiglottis projects posterosuperiorly from its stem-like base, which is attached to the thyroid cartilage. It ...
Epiglottitis is a life-threatening condition caused by inflammation of the epiglottis and aryepiglottic folds 1, which can lead to acute airway obstruction. Treatment should be urgent and performed by appropriately trained individuals, e.g. instrumentation of the trachea should be performed by ...
Epignathus is a term given to a very rare form of teratoid tumor that arises from the oropharyngeal region.
There may be a slight female predilection ref. The estimated incidence is ~ 1 in 35,000 to 200,000 births.
The tumor classically presents in utero or...
Epiphora represents excessive tearing of the eye and is a common clinical presentation to ophthalmological practice. It is most frequently due to an obstruction of the nasolacrimal drainage apparatus. Less commonly, overproduction of tears may be responsible.
Epistaxis (plural: epistaxes) is the medical term for a nosebleed, and is very common in clinical practice with a broad differential diagnosis. Anterior epistaxes mainly bleed from Kiesselbach's plexus and posterior epistaxes (5% of all epistaxis) from Woodruff's plexus.
The epitympanum, also known as the attic or epitympanic recess, is the most superior portion of the tympanic cavity. It is that portion of the tympanic cavity superior to the axial plane between the tip of the scutum and the tympanic segment of the facial nerve 1,3.
Posteriorly the epitympanum ...
Ethmocephaly refers to a rare type of midline cranio-facial anomaly that is characterized by the presence of extreme hypotelorism, arhinia and a midline proboscis.
holoprosencephaly 1,2: particularly alobar holoprosencephaly
The ethmoidal air cells, also known less commonly as the ethmoidal sinuses, form one of the four pairs of paranasal sinuses. They are located within the single, midline ethmoid bone.
location: between the orbit and the nasal cavity, within the ethmoid labyrinth of the ethmoid bone
The ethmoid bone is a single midline facial bone that separates the nasal cavity from the brain and is located at the roof of the nose and between the orbits. It is a cubical shape and is relatively lightweight because of its spongy construction. It contributes to the anterior cranial fossa.
The ethmoid bulla, also known as bulla ethmoidalis, is the largest and most consistent air cell of the anterior ethmoid air cells.
It is located posterior to the frontal recess and enclosed laterally by the lamina papyracea. It forms the roof of the middle meatus.
It can be clas...
The ethmoid infundibulum is a curved cleft of the ethmoid bone which leads into the anterior portion of the hiatus semilunaris. It is bordered medially by the uncinate process and laterally by the orbital plate of the ethmoid. The infundibulum is often continuous with the frontal recess into whi...
An ethmoid mucocele is a form of a paranasal sinus mucocele involving the ethmoid air cells. Depending on its anterior and/or posterior location, they can also include nasoethmoid and sphenoethmoid mucoceles. Ethmoid mucoceles are considered the second most commonest in location 2.
The Eustachian tube, also known as the pharyngotympanic tube or auditory tube, is the channel via which the tympanic cavity communicates with the nasopharynx. It is ~36 mm in length and is directed downward, forward, and medially, forming an angle of about 45 degrees with the sagittal plane and ...
Eustachian tube dysfunction (ETD) is considered by many to be the underlying cause of chronic otomastoiditis, although both the exact pathogenesis and role of ETD in chronic middle ear infections is unclear.
ETD is estimated to be present in ~1% of the adult population.
The external auditory canal (EAC) or external auditory meatus (EAM) extends from the lateral porus acusticus externus medially to the tympanic membrane.
As the term external auditory meatus (EAM) is variably used to refer to the canal or the porus acusticus externus (the round late...
External auditory canal atresia (EACA) is characterized by complete or incomplete bony atresia of the external auditory canal (EAC) and, especially when seen in the setting of an associated syndrome, a dysplastic auricle and an abnormal middle ear cavity.
The incidence is 1 in 10,...
External auditory canal cholesteatomas are uncommon locations for cholesteatomas, which are usually in the middle ear or petrous apex. When they occur lateral to the tympanic membrane, they are referred to as external auditory canal cholesteatomas.
The external acoustic canal i...
Exostosis of the external auditory canal (also known as surfer's ear), is a benign bony overgrowth of the bony external auditory canal brought about by exposure to cold wind and water combined.
broad-based or more focal circumferential bony overgrowth of the osseous exter...
External auditory canal osteomas are rare focal pedunculated bony overgrowths of the osseous external auditory canal.
solitary pedunculated bony overgrowth of the external auditory canal usually at the bony cartilaginous junction
large lesions may be associat...
The external carotid artery (ECA) is one of the two terminal branches of the common carotid artery. The other terminal branch is the internal carotid (ICA), which is somewhat larger than the ECA.
origin: bifurcation of the common carotid artery
course: under the submandibular gland an...
The external ear comprises the auricle (or pinna), the external auditory meatus, and the tympanic membrane (eardrum). The auricle concentrates and amplifies sound waves and funnels them through the outer acoustic pore into the external auditory meatus to the tympanic membrane.
The external jugular vein (EJV) drains the head, face and part of the pectoral region.
Origin and course
The posterior division of the retromandibular vein and posterior auricular vein unite to form the external jugular vein at the angle of the mandible.
It courses inferiorly i...
A mnemonic to remember external jugular vein (formed by the retromandibular and posterior auricular veins) tributaries is:
P: posterior external jugular vein
A: anterior jugular vein
S: suprascapular vein
T: transverse cervical vein
The extraconal orbital compartment or extraconal space is the space within the orbit outside the musculofascial cone. The base of which is anterior and is formed by the orbital septum that surrounds the equator of the globe. The external sides are formed by the bones of the orbit and their perio...
Extraconal orbital lesions include lesions which arise from structures within the extraconal orbital space and those extending from adjacent structures into the orbits.
dermoid cyst: most common lesion in pediatrics
lacrimial gland lesions
Extracranial meningiomas, also known as primary extradural meningiomas or ectopic meningioma, are a rare location-specific type of meningioma that arise outside the dural covering of the brain and spinal cord. They are essentially extracranial tumors, most often occurring in the head and neck, m...
Extramedullary plasmacytoma, also known as extraosseous plasmacytoma, are the less common form of solitary plasmacytoma, manifesting as isolated plasma cell tumors located at a non-osseous site. In contrast to multiple myeloma (MM), solitary plasmacytoma have little or no systemic bone marrow in...
An extramural air cell is one that is not contained within its named parent bone. So, the infraorbital ethmoidal air cells that lie within the maxilla rather than the ethmoidal bone are an example of extramural air cells.
A mnemonic to remember the order in which extraocular muscles are involved in thyroid-associated orbitopathy (TAO) is:
I: inferior rectus
M: medial rectus
S: superior rectus
L: lateral rectus
O: obliques muscles (superior oblique and inferior oblique)
There is some deba...
A mnemonic to remember the nerve supply to the extraocular muscles:
LR6SO4O3 (mock 'chemical formula')
The letters represent the extraocular muscles and numbers represent their respective cranial nerve supply:
LR6: lateral rectus, innervated by the 6th (abducens) nerve
The extraocular muscles are the six muscles that insert onto the eye and hence control eye movements:
superior rectus: elevation
superior oblique: intorsion
medial rectus: adduction
lateral rectus: abduction
inferior oblique: extorsion
inferior rectus: depression
The extrinsic muscles of the tongue are a group of 4 muscles of the tongue. They all arise outside the tongue, which is in comparison to the intrinsic muscles of the tongue which are entirely within the tongue with no external attachments. They act to alter the position of the tongue where as th...
The extrinsic muscles of the tongue can be remembered with the following mnemonic:
Paris St Germain's Hour
Paris St. Germain's Hour
Exudative retinitis, also known as retinal telangiectasis or Coats disease, is a rare congenital disease affecting the eyes and is a cause of leukocoria.
It occurs predominantly in young males, with the onset of symptoms generally appearing in the first decade of life with a peak ...
The eyelid covers the eye and is covered in front with loose skin and behind with adherent conjunctiva. The lower lid possesses very little mobility; lids are closed gently by palpebral fibers and forcefully by orbicularis oculi.
The eyelid comprises of a number of key features ...
Eye movements are a complex set of movements of the globe that are performed by the extraocular muscles that are grouped by the muscles that perform particular movements:
ocular internal rotators
ocular external rotators
Facial angiofibroma, also known as fibrous papule, is a fairly common skin lesion seen in males and females after puberty.
They represents a focal vascular and collagen growth.
This lesion is usually solitary and located on the nose skin, measuring 1-5 mm.
There is no hereditary p...