The orbit is a feature of the face and contains the globe and it's supporting structures, as well as many nerves and vessels.
In the adult, the orbit has a volume of approximately 30 mL, of which the globe occupies 6.5 mL. It has a roof, floor, medial and lateral wall. The orbit ...
The orbital apex refers to the posterior confluence of the orbit at the craniofacial junction, where nerves and vessels are transmitted from the intracranial compartment into the orbit via several bony apertures. It is also the point where the extra-ocular muscles derive their origins.
Orbital blow-in fractures occur when there is displacement of bone fragments towards the orbits.
blow-in fracture effectively reduces the volume of the orbit
associated intraorbital injuries include extraocular muscle entrapment and optic nerve injury
as an isolated (pure) orbital ...
Cavernous venous malformations of the orbit, also known as cavernous haemangiomas, are the most common vascular lesion of the orbit in adults.
It is important to note that according to newer nomenclature (ISSVA classification of vascular anomalies) these lesions are merely known as slow flow ve...
Several cystic and cyst-like orbital lesions may be encountered in imaging of the orbits:
developmental orbital cysts
dermoid: commonest benign orbital tumour in childhood
congenital cystic eye
Orbital dermoid cysts are congenital lesions representing closed sacs lined by an ectodermal epithelium and comprising the most common orbital tumour in children. They are typically divided into deep (within the orbit) and superficial (adjacent to the orbital rim).
They comprise ~...
Orbital emphysema is the presence of gas within the orbital soft tissues. It is usually due to orbital fractures communicating with the paranasal sinuses but can be caused by penetrating trauma and infection. It is a common finding also after orbital or ocular surgery.
Orbital infection is a relatively commonly encountered pathology.
It comprises of three main clinical entities with the most important distinction between that of orbital and periorbital cellulitis:
periorbital cellulitis (preseptal cellulitis) is limited to the soft tissues anterior to the or...
The differential diagnosis of orbital inflammatory diseases (including orbital pseudotumours) can be divided based on their location into:
dacryoadenitis of lacrimal glands
myositis of extraocular muscles
perineuritis of optic nerve
Primary lymphoma of the orbit is one of the commonest orbital tumours and accounts for as much as half of all orbital malignancies. It is a B-cell non-Hodgkin lymphoma, and in most cases arises from mucosa-associated lymphoid tissue (MALT).
Orbital lymphomas account for only 2% of...
Orbital lymphoproliferative lesions compromise a wide spectrum of diseases ranging from benign to malignant.
Patient's may present with a palpable mass or proptosis. Pain is an uncommon symptom unlike orbital pseudotumour, which manifests with acute pain.
An orbital mass carries a relatively wide differential:
lacrimal gland or duct tumours
rhabdomyosarcoma of the orbit
optic nerve meningioma
optic nerve glioma
optic nerve schwannoma
developmental orbital cysts 3:
Meningiomas of the orbit are uncommon. They can be divided into two broad categories:
primary orbital meningioma
almost all are optic nerve meningiomas
rarely ectopic rests of arachnoid cells give rise to orbital meningiomas separate from the optic nerve sheath 1
secondary orbital meningioma...
Orbital metastases are relatively uncommon, but some primary tumours do have a predilection to metastasise to the orbit.
This article concerns itself with extraocular metastases, rather than intraocular tumours or direct extension of tumours from neighbouring regions. For a discussion of intrao...
There are numerous nerves of the orbit with have varying functions. There are best described divided into groups based on how they enter the orbit.
optic nerve (CN II): special sensory nerve of the globe (vision)
Superior orbital fissure
superior division of the oculomotor nerve ...
Orbital pathology covers a variety of diverse diseases that affect the orbit. The complicating factor is that the orbit is composed of a large number of different tissues which each have a plethora of pathologies that can affect them.
For simplification, they can be separated i...
Orbital pseudotumour is an idiopathic inflammatory condition that most commonly involves the extraocular muscles. Less commonly there is inflammatory change involving the uvea, sclera, lacrimal gland, and retrobulbar soft tissues. The exact aetiology is not known but an association with many inf...
The orbital septum is a thin sheet of fibrous tissue that originates from the orbital rim periosteum and blends with the tendon of the levator palpebrae superioris superiorly and inserts into the tarsal plate inferiorly.
The orbital septum separates the intra-orbital fat from eyelid fat and orb...
The orbital spaces are important when considering different pathologies:
subdivided into anterior and posterior segments by the lens
optic nerve-sheath complex
central retinal artery and vein
surrounding sheath of meninges as an extension of the cerebr...
Orbital vascular lesions may be difficult to distinguish on imaging. However, the following conditions have been described:
lymphangioma / lymphangiovenous malformation / venolymphatic malformation
orbital venous malform...
Orbital venous varix (OVV) is an uncommon vascular malformation which is composed of enlarged single or multiple tubular venous channels with direct communication to the systemic venous system.
Orbital venous varices are divided into primary and secondary. Primary orbital varices ...
The organ of Corti, also known as spiral organ, is the receptor organ for hearing, located in the cochlea (housed inside the scalae mediae). It is a strip of sensory epithelium made of hair cells which act as the sensory receptors of the inner ear.
This is a vulgarisation of the compl...
Oro-antral fistula (OAF) is a pathological communication between the oral cavity and the maxillary sinus (antrum).
There is a slightly greater male predilection 2.
Oro-antral fistulas may be subtyped by location into:
T staging of oropharyngeal tumours is as follows:
The oropharynx includes the base of the tongue, the inferior surface of the soft palate and uvula, the anterior and posterior tonsillar pillars, the glossotonsillar sulci, the pharyngeal tonsils, and the lateral and posterior pharyng...
The oropharynx forms part of the pharynx, being the continuation of oral cavity and nasopharynx superiorly, and the larynx and hypopharynx inferiorly.
The oropharynx is the posterior continuation of the oral cavity and the inferior continuation of the nasopharynx.
Oscillopsia (also known as Dandy syndrome or jumbling of the panorama) is the inability to maintain horizon while walking.
Since our heads bob up and down while walking, the otolithic system controls eye movement to maintain a constant horizon when walking. When there is bilateral absent vestib...
Ossicular chain disruption (or ossicular discontinuity) is loss of normal alignment between the three middle ear ossicles. The condition is a cause of conductive hearing loss.
Exact incidence and prevalence are not known. Hearing loss associated with temporal bone fractures in chi...
Ossicular chain fixation refers to the presence of fibrous tissue (chronic adhesive otitis media) which usually appears as noncalcified, soft-tissue density encasing some or all of the ossicular chain.
It may be present in the meso- and epitympanum yet it usually occurs in the niche of oval win...
Osteoarthritis of the temporomandibular joint (TMJ) is the end point of long-standing TMJ dysfunction. It is a common finding incidentally on a base of skull imaging, and it should be remembered that TMJ pain does not correlate well with osteoarthritic changes. Indeed pain from TMJ dysfunction i...
Osteomas are benign mature bony growths, seen almost exclusively in bones formed in membrane (e.g. the skull).
When they arise from bone they may be referred to as a "homoplastic osteoma", and when they arise in soft tissue they may be referred to as a "heteroplastic osteoma".
The ostiomeatal complex (OMC) or ostiomeatal unit (OMU), sometimes less correctly spelled as osteomeatal complex, is a common channel that links the frontal sinus, anterior ethmoid air cells and the maxillary sinus to the middle meatus allowing airflow and mucociliary drainage.
A useful mnemonic to remember the five parts of the ostiomeatal complex is:
H: hiatus semilunaris
E: ethmoidal bulla
M: maxillary ostium
U: uncinate process
Emus have large beaks, and hence could have large ostiomeatal complexes (if they had paranasal sinu...
Some ostiomeatal complex anatomical variations, which do not characterise disease by itself, can promote narrowing and even obstruction 1:
concha bullosa ~10% (range 4-15%) - aerated middle turbinate
intralamellar cell: air cell within vertical portion of the middle turbinate
The Ostmann fat pads (also somewhat lewdly known as Ostmann fatty bodies) are located inferomedial to the Eustachian tubes and is thought to be important in normal closure, preventing transmission of nasopharyngeal pressure to the middle ear. Failure to visualize this thin triangular fat pad is ...
The otic capsule refers to the dense osseous labyrinth of the inner ear that surrounds the cochlea, the vestibule and the semicircular canals. It is surrounded by the less dense / pneumatised petrous apex and mastoid part of the temporal bone.
petrous temporal bone fractures...
The otic ganglion is one of four parasympathetic ganglia of the head and neck. It receives parasympathetic fibres from the glossopharyngeal nerve.
small and disc shaped
located in the infratemporal fossa
it lies immediately below the foramen ovale, medial to the mandibular divi...
Otitis externa refers to inflammation of the external ear.
It is quite a common condition and may affect up to 10% of people during their lifetime.
It can present in several forms:
acute otitis externa
chronic otitis externa
necrotising otitis externa
Otitis media refers to inflammation or infection of the middle ear cavity. It is commonly seen in children and is termed otomastoiditis when inflammation spreads to involve the mastoid.
Common complaints include otalgia, otorrhoea, headache, fever, and systemic upset. In ...
Otorrhagia denotes haemorrhage from the external acoustic meatus and is commonly seen in the setting of petrous temporal bone fractures or soft tissue injuries to the external or middle ear. Rarely an internal carotid artery aneurysm with dehiscence into the middle ear can present with spontaneo...
Otosclerosis (also known as otospongiosis) is an idiopathic slowly progressive primary disorder of the bony labyrinth. It is one of the leading causes of deafness in adults.
The term otosclerosis is somewhat of a misnomer. Much of the clinical course is characterised by lucent rat...
Otosyphyilis, otic syphilis or syphilitic labyrinthitis is a manifestation of neurosyphilis affecting the inner ear.
For a general discussion, and for links to other system specific manifestations, please refer to the article on syphilis.
The pathological features of syphilitic lab...
Oval window atresia or congenital absence of oval window shows absent cleavage plane between the lateral semicircular canal above and cochlear promontory below associated with anomalous stapes and malpositioned facial nerve (cranial nerve VII).
Profound conductive hearin...
Oxalosis results in supersaturation of calcium oxalate in the urine (hyperoxaluria), which in turn results in nephrolithiasis and cortical nephrocalcinosis.
This article focus on the secondary oxalosis, please refer to primary oxalosis for a specific discussion on this entity.
P16 is a widely used immunohistochemical marker. It can be expressed in other neoplasms and in several normal human tissues. It can play an important role gynecological malignancy and is a surrogate marker for HSIL's (high-grade squamous intraepithelial lesions). It has been applied to facilitat...
The differential diagnosis of paediatric cervical lesions is commonly encountered in practice, unfortunately, the list is long.
Most lesions tend to be inflammatory 3:
infected branchial cle...
Tumours of the posterior fossa in children can be remembered using the mnemonic:
The mnemonic is not in order of prevalence; pilocytic astrocytomas are most common.
B: brainstem glioma
A: astrocytoma (pilocytic) (85%)
The palate is the partition between the oral and nasal cavities, forming the roof of the oral cavity and the floor of the nasal cavity. It is composed of the osseous fixed hard palate comprising the anterior 2/3rds of the palate and a mobile soft palate devoid of bone and with multiple functions...
The palatine bones are paired L-shaped bones joined at the midline. They form the hard palate with the maxillary bones. They also form part of the floor of the nasal cavity (the hard palate separates the oral cavity from the nasal cavity).
The palatine bones are located at the b...
The palatine tonsil, referred simply to as "the tonsils" when considered together bilaterally, is a collection of lymphoid tissue in the pharyngeal mucosa.
It is often described to have two borders, two poles and two surfaces:
anterior and posterior borders (described in relatio...
The palatoglossus muscle is one of the four extrinsic muscles of the tongue. The paired muscles create ridges of mucous membrane in the lateral pharyngeal wall called the palatoglossal arches (also know as the anterior pillars of the fauces). These form the lateral boundary between the oral cavi...
The palatopharyngeus is a muscle of the head and neck, and one of the inner longitudinal muscles of the pharynx. It is also referred to as one of the five paired muscles of the soft palate. The paired muscles create ridges of mucous membrane in the lateral pharyngeal wall called the palatophary...
The palatovaginal canal is a small short canal located at the articulation of the sphenoidal process of palatine bone and the vaginal process of the medial pterygoid plate of the sphenoid bone.
It transmits the pharyngeal nerve, a branch of the maxillary division of the trigeminal nerve (CN Vb)...
Papillary thyroid carcinoma (PTC) is the most common malignancy of the thyroid gland, and frequently has nodal metastases at presentation.
Papillary thyroid cancer (as is the case with follicular thyroid cancer) typically occurs in the middle-aged, with a peak incidence in the 3rd...
Paradoxical middle turbinate is a rare developmental cause of nasal obstruction. It refers to an inferomedially curved middle turbinate edge with the concave surface facing the nasal septum and usually occurs bilaterally.
Paradoxical middle turbinate is a rarely encountered anomal...
Paragangliomas, sometimes called glomus tumours, are slow growing tumours arising from non-chromaffin paraganglion cells that are scattered throughout the body from the base of skull to the urinary bladder.
Paragangliomas are sometimes referred to as glomus tumours although this gi...
Paragangliomas of the head and neck are rare tumours, representing <0.5% of all head and neck tumours.
For a general discussion of the pathology of these tumours please refer to the paraganglioma article.
Overall there is a 3:1 female predominance, with two-thirds of cases being ...
The paranasal sinuses usually consist of four paired air-filled spaces. They have several functions of which reducing the weight of the head is the most important. Other functions are air humidification and aiding in voice resonance. They are named for the facial bones in which they are located:...
Retention cysts of paranasal sinuses are benign lesions usually discovered incidentally on a plain sinus radiograph or cross-sectional imaging of the head. They do not usually cause symptoms.
They are also referred to as mucous retention cysts.
It is difficult to es...
Paranasal sinuses are air-filled cavities surrounding the nasal cavity proper which includes maxillary sinus, sphenoid sinus, frontal sinus and ethmoid sinus. Trauma to the superior and middle thirds of the face can often lead to in paranasal sinus fractures involving one or more paranasal sinus...
Paranasal sinus mucoceles represent complete opacification of one or more paranasal sinuses by mucus, often associated with bony expansion due to obstruction of the nasal sinus drainage.
Clinical presentation depends on two factors:
location and direction of expansion
Paranasal sinuses mycetoma are indolent and non-invasive fungal colonisation of the paranasal sinuses.
Pathogenesis is thought to be a cascade of processes from insufficient mucociliary clearance leading to sinus colonisation and chronic inflammatory response. The patient may only ...
Osteoma of the paranasal sinuses is a common benign tumour, usually found incidentally.
Osteomas are commonly found in patients undergoing imaging of the sinuses, appearing in up to 3% of CT examinations of the paranasal sinuses 1. They are most frequently diagnosed in 20-50 years...
Parapharyngeal abscesses are deep neck abscesses involving the parapharyngeal space. It is a serious medical condition, potentially fatal, and requires prompt diagnosis treatment.
A person of any age can develop a parapharyngeal abscess, but it is most commonly seen in children an...
The parapharyngeal space is one of the seven deep compartments of the head and neck. It consists largely of fatty areolar tissue and contains branches of the trigeminal nerve as well as deep vessels.
The parapharyngeal space is shaped like a pyramid, inverted with its base at the...
The parasympathetic ganglia are a group of 4 bilateral automonic ganglia in the head and neck which receive parasympathetic fibres from the autonomic components of the cranial nerves III, VII and IX. They are involved in parasympathetic control of the eye, major and lesser salivary glands and t...
Parathyroid adenomas are benign tumours of the parathyroid glands, and are the most common cause of primary hyperparathyroidism.
Patients present with primary hyperparathyroidism: elevated serum calcium levels and elevated serum parathyroid hormone levels. This results in...
The parathyroid glands are endocrine glands located in the visceral space of the neck. They produce parathyroid hormone, which controls calcium homeostasis.
There are normally two pairs of parathryoid glands, inferior and superior, although there can be up to twelve in number. T...
Parathyroid hormone (PTH), also known as parathormone, is secreted by the parathyroid glands in response to hypocalcaemia. Its main physiologic effects are to
increase osteoclastic activity in bone
increase renal reabsorption of calcium
inhibit renal absorption of phosphate and bicarbonate
Parathyroid hyperplasia is the diffuse enlargement of the parathyroid glands and is a less common cause of primary hyperparathyroidism.
There is a female predilection (M:F = 1:3).
Most commonly an incidental finding of hypercalcaemia in asymptomatic patie...
The parietal bone is a paired, irregular, quadrilateral skull bone that forms the sides and roof of the cranium.
The parietal bone has four borders, four angles, and external/internal surfaces.
Borders include: frontal, sagittal, occipital (half of lambdoid suture), and squamou...
The parietal foramen is a foramen on each side of the posterior aspect of the parietal bone near the sagittal suture. It transmits the emissary veins draining to superior sagittal sinus and occasionally a branch of the occipital artery. It has a variable appearance and is often absent 3. When bo...
Parietal foramina are a type of congenital calvarial defect. They result from delayed/incomplete ossification of the parietal bone.
They can occur as an isolated autosomal dominant trait or as part of a syndrome. Ossification along a midline bar may separate confluent parietal defect...
The parietotemporal/parietomastoid suture represents the articulation between the parietal and temporal bones posteriorly. Anteriorly, they articulate at the squamosal suture. The parietotemporal suture is considered the most posterior continuation of squamosal suture and is at times interrupted...
The parotid duct, also known as Stensen duct, drains saliva from the parotid gland into the oral cavity. It secretes primarily serous saliva.
The parotid duct is approximately 5cm long and passes anteriorly through the buccal fat superficial to the masseter muscle and over its an...
Parotid enlargement has a wide differential given the significant breadth of pathology that can affect the parotid gland. These can be separated by the standard surgical sieve approach into infective, inflammatory, immune, neoplastic, infiltrative and congenital causes.
The parotid gland is the largest of the salivary glands and secretes saliva via the parotid duct into the oral cavity to facilitate mastication and swallowing. It is located in the parotid space.
The parotid gland is wrapped around the mandibular ramus and extends to a position ...
The parotid space is one of the seven deep compartments of the head and neck and as the name suggests is mostly filled with the parotid gland. It is the most lateral major suprahyoid neck space.
The parotid space is a roughly pyramidal space, the broad elongated base facing later...
The pars flaccida is the flaccid portion of the tympanic membrane and represents a small portion of the membrane.
It extends upwards from the anterior and posterior malleolar folds at the level of the lateral process of malleus. Hence, it sits between the scutum and malleus.
The pars tensa is the tense portion of the tympanic membrane and refers to the main portion of the membrane.
It extends from the anterior and posterior malleolar folds at the level of the lateral process of malleus to the inferior extent of the tympanic membrane at its attachment.
The Passavant cushion is a small prominence in the posterior pharynx, formed from a focal bulge of the superior pharyngeal constrictor muscles during swallowing.
The "cushion" opposes the soft palate during the act of swallowing and is part of the seal between soft palate and pharynx that preve...
Recognising patterns of sinonasal obstruction is useful to help localise the area of pathology and narrow the differential diagnosis.
Babbel et al described five pattern of sinonasal obstruction 1, which are readily apparent on CT:
Patulous tube syndrome (PTS), is a form of Eustachian tube dysfunction. Whereas the normal dysfunction of failure of the tube to open normally, in PTS the tube remains abnormally open allowing transmission of nasopharyngeal pressure to the middle ear.
During strong inspiration (i.e 'sniff') t...
A pedunculated intratracheal mass has a variety of differential diagnoses:
benign tumour, e.g. hamartoma, chrondroma, lipoma
metastasis to tracheal mucosa, e.g. renal cell carcinoma, melanoma
polyp, e.g. inflammatory, antrochoanal
Pendred syndrome is an autosomal recessively inherited disorder characterised by a euthyroid goitre associated with sensorineural hearing loss.
It is considered the most common form of syndromic hearing loss and accounts for upwards of 10% of hereditary deafness.
Penetrating traumatic neck injury can be a potentially devastating injury due to the high density of crucial anatomical structures within the neck.
Young males are highly represented in patients with a traumatic neck injury. In one study, 11:1 ratio of males to females were ident...
Periapical cysts, also known as radicular cysts, are the most frequent cystic lesion related to teeth (see mandibular lesions) and result from infection of the tooth.
On imaging, they generally appear as a round- or pear-shaped, unilocular, lucent lesion in the periapical region, measuring <1 c...
Perilymph is a one of two type of cochlear fluids, the other being endolymph. It is located in the scala vestibuli and scala tympani of the cochlea.
It is very similar to cerebrospinal fluid as the scala tympani and scala tympani communicate directly with the subarachnoid space.
It has a high ...
A perilymphatic fistula (PLF) (also known as a labyrinthine fistula) is a pathologic communication between the fluid-filled space of the inner ear and the air-filled space of the middle ear, most commonly occurring at either the round or oval window.
The primary manifestations of perilymphatic...
Perineural spread of tumour is a form of local invasion in which primary tumours cells spread along the tissues of the nerve sheath. It is a well-recognised phenomenon in head and neck cancers.
An important distinction has to be made between perineural invasion (PNI) and Perineural spread (PNS...
Peritonsillar abscess or quinsy is the most common deep neck infection.
Peritonsillar abscesses are most common in 20-40 year olds with a predominance for males and for smokers. It is less common in children but immunosuppression increases the risk of development 2-3.
The perivertebral space is one of the seven deep compartments of the head and neck.
The perivertebral space is a cylinder of soft tissue lying posterior to the retropharyngeal space and danger space surrounded by the prevertebral layer of the deep cervical fascia and extends from...
Persistent hyperplastic primary vitreous (PHPV), also known as the persistent fetal vasculature, refers to a rare congenital developmental malformation of the eye.
Clinically, this condition usually manifests as unilateral or bilateral leucocoria. Patients may also have p...
Persistent hypophyseal canal, also known when larger than 1.5mm in diameter as the craniopharyngeal canal, is a rare congenital defect characterised by a communication through the central skull base between the nasopharynx and the pituitary fossa.
There are a number of terms which...