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%)
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...
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 bladder.
Paragangliomas will be discussed separately depending on their location:
paragangliomas of the ...
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 bei...
Paranasal sinus mucocoeles 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...
The paranasal sinuses consists of, usually, 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. There are named for the facial bones in which they are loca...
Retention cysts of paranasal sinuses are usually discovered incidentally on a plain sinus radiograph or cross-sectional imaging of the head. They do not usually cause symptoms.
They are slow growing lesions, but mucosal and cortical integrity is preserved.
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 and...
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...
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 (parathormone) levels. ...
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 hyperplasia is the diffuse enlargement of the parathyroid glands and is a cause of primary hyperparathyroidism.
There is a female predilection (M:F = 1:3).
Most commonly an incidental finding of hypercalcaemia in asymptomatic patients.
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 suture represents the articulation between the parietal and temporal bones posteriorly. Anteriorly, they articulate at the squamosal suture. The parietotemporal suture is considered the posterior most continuation of squamosal suture and is at times interrupted by the squamom...
The parotid duct, also known as Stensen's duct, connects the parotid gland and the buccal mucosa.
The parotid duct passes through the buccal fat, buccopharyngeal fascia and the buccinator muscle. Its opening to vestibule of the mouth occurs next to the upper second molar tooth at...
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 ...
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...
A predunculated 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.
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 present as round or pear-shaped, unilocular, lucent lesions in the periapical region, measuring less ...
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 tumour spread is a form of metastatic disease in which primary tumours cells spread along the tissues of the nerve sheath, being a well recognised phenomenon in head and neck cancers.
Perineural tumour spread is more frequently associated with 1,2,5:
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...
The ossiculum terminale appears as a secondary ossification centre of the dens between 3-6 years and normally fuses by 12 years. Failure of fusion results in a persistent ossiculum terminale (also called Bergmann's ossicle or ossiculum terminale of Bergmann) and is considered a normal anatomical...
The persistent stapedial artery (PSA) refers to failure of regression of the embryonic stapedial artery.
It's prevalence is thought to range around 0.02-0.48% in the population.
incidental finding during surgery
conductive hearing loss ...
Petroclival suture is a short cranial suture between the medial tip of petrous bone and superolateral border of the clivus. It is een in continuation with the petro-occipital groove and the carotid canal is immediately anterior to this suture.
Petromastoid canal or subarcuate canal joins the mastoid antrum to the posterior cranial fossa 1 and contains the subarcuate vein and artery.
type I - invisible
type II - less than 0.5 mm width
type III - 0.5-1 mm width
type IV - greater than 1 mm width 1
Petrosquamous suture is a shallow bony fissure between the medial horizontal petrous part and lateral vertically oriented squamous part of temporal bone.
At times, this cranial suture may house a small emissary vein which can bleed at the time of surgeries.
The petrotympanic fissure is a small fissure in the temporal bone. It divides the mandibular fossa anteriorly by the articular tubercle and posteriorly by the tympanic part of the temporal bone. The chorda tympani runs through the fissure into the infratemporal fossa.
Petrous apicitis, also known as apical petrositis, is infection with involvement of bone at the very apex of the petrous temporal bone.
Petrous apicitis is less common than it once was, on account of the widespread and early use of antibiotics for acute otomastoiditis 3-4.
The petrous part of the temporal bone (or more simply petrous temporal bone) forms the part of skull base between the sphenoid and occipital bones.
The petrous temporal bone (PTB) has a pyramidal shape with an apex and a base as well as three surfaces and angles:
A handy mnemonic to recall the complications of transverse and longitudinal petrous temporal bone fractures is:
listen carefully to something funny
listen carefully = longitudinal / conductive hearing loss
to something funny = transverse / sensorineural hearing loss and facial nerve...
The pharyngeal (or superficial) mucosal space is one of the seven deep compartments of the head and neck. It consists of the mucosa and structures deep to the mucosa of the nasopharynx, the oropharynx, and the laryngopharynx.
The pharyngeal mucosal space is the most internal comp...
The pharyngeal nerve is a branch of the maxillary division of the trigeminal nerve which enters the pterygopalatine ganglion
exits the pterygopalatine ganglion in the pterygopalatine fossa
passes through the palatovaginal canal with the pharyngeal branch of the maxillary...
The phrenic nerve is a mixed motor/sensory nerve that courses through the neck and thorax to innervate the diaphragm.
Arises from the ventral rami of the C3, C4 and C5 nerve roots, part of the cervical plexus.
In the neck, the phrenic nerve lies on the anterior s...
Phthisis bulbi, also known as end-stage eye, is an atrophic scarred and disorganised globe that may result from a variety of severe ocular insults.
The globe is reduced in size (usually < 20 mm) with a thickened/folded posterior sclera. Dystrophic calcification is common, and oss...
A pilomatricoma is an uncommon, benign neoplasm thought to arise from hair cortex cells. It was formerly referred to as pilomatrixoma or calcifying epithelioma of Malherbe.
the reported incidence ranges between 1 in 500-2000
they make up 0.12% of cutaneous neoplasms and 20% of al...
A useful mnemonic for remembering the differential for pituitary region masses is:
S: sarcoid, sellar tumour (pituitary adenoma)
T: teratoma or tuberculosis (and other granulomatous diseases)
C: craniopharyngioma, cleft cyst (Rathke), chordoma
Platybasia is characterised by abnormal flattening of the skull base as defined by measuring the base of skull angle >143º.
Platybasia alone does not usually cause symptoms unless it is associated with basilar invagination.
Pleomorphic adenomas, also known as benign mixed tumours (BMT's), are the most common salivary gland tumours.
Pleomorphic adenomas account for 70-80% of benign salivary gland tumours and are especially common in the parotid gland (see below) 1,6. Patients are typically in their mi...
Plummer-Vinson syndrome (also known as the Paterson-Brown-Kelly syndrome) predisposes to hypopharyngeal squamous cell carcinoma and consists of four features:
oesophageal webs or hypopharyngeal webs
The condition is more common in women, and is ...
Pneumatisation of the dorsum sella is not uncommon, but needs to be remembered as an unusual site of sinus disease, which otherwise may be mistaken for intracranial of pituitary disease.
Pneumoparotid refers to air in the parotid gland and can cause unilateral/bilateral parotid swelling. In severe cases it can be associated with subcutaneous emphysema.
Any profession or recreation that increases oral positive pressure can cause air to reflux up the parotid ducts int...
Pneumosinus dilatans is a term given to enlarged paranasal sinus air cells (hyperpneumatisation), which may cause pneumocephalus either by rupturing or because of a defect. It was initially described in the frontal sinuses, but may involve any of the paranasal sinus.
The presence of pneumosinus...
Pöschl projection is used in imaging the temporal bone. The plane of projection is perpendicular to the long axis of the temporal bone. In the Pöschl projection the temporal bone is imaged from its anteromedial to posterolateral aspects.
Positional plagiocephaly, also known as deformational plagiocephaly, refers to a calvarial deformation that results from external pressure after birth when an infant is consistently placed in the same position for rest and sleep. It can be marked in very premature infants, whose heads become fla...
Post partum thyroiditis (PPT) is a type of thyroid inflammatory condition that precipitates following childbirth. It may also occur following a spontaneous or induced abortion.
The estimated incidence is thought to be around 5-9% of postpartum women. 3.
The posterior auricular artery is a branch of the external carotid artery and supplies scalp posterior to the auricle and the auricle itself.
origin: branch of the external carotid artery above digastric and stylohyoid opposite the styloid process...
The posterior cranial fossa is the most posterior aspect of the skull base and it houses the brainstem and cerebellum.
The following structures are present from anterior to posterior:
internal acoustic meatus
groove for superior petrosal sinus
The posterior external jugular vein is a tributary of the external jugular vein.
Origin and course
Forms from the confluence of several superficial veins in the posterosuperior neck and posterior scalp. It passes superficially over the posterior triangle to drain into the extern...
The posterior lacrimal crest is a bony projection on the lacrimal bone which creates the medial margin of the lacrimal sac fossa.
anterior lacrimal crest
Postoperative assessment after thyroid cancer surgery is performed in the surgical bed and regional lymph nodes, looking for possible recurrence of disease.
usually performed in first 6-12 months, and then as needed by the patient's risk factors 1
Pott puffy tumour is a non-neoplastic complication of acute sinusitis characterised by subperiosteal abscess and osteomyelitis, usually related to the frontal sinus but sometimes also related with the mastoid. Forehead swelling is seen, which explains the name of this pathology.
Other rare caus...
Powers ratio is a measurement of the relationship of the foramen magnum to the atlas, used in the diagnosis of atlanto-occipital dissociation injuries.
The ratio, AB/CD, is measured as the ratio of the distance in the median (midsagittal) plane between the:
basion (A) and the posterior spinola...
Primary idiopathic hypothyroidism with thyroid atrophy (or Ord disease) is one of the causes of hypothyroidism. Some aothors consider this entity as being on the same spectrum as Hashimoto disease while others consder it as distinct entities.
The thyroid gland...
There are a number of primary malignancies of the nasopharynx:
nasopharyngeal carcinoma (squamous cell carcinoma): 70%
lymphoma (sinonasal lymphoma): 20%
adenoid cystic carcinoma
Malignant uveal melanoma is the most common primary tumour of the adult eye 3.
Malignant melanoma of the uvea is most common primary intraocular malignancy, and is predominantly seen in Caucasians 5. The incidence of these tumours increases with age, with only 2% of tumours found ...
Proptosis refers to forward protrusion of the globe with respect to the orbit. There are many causes of proptosis which can be divided according to location and it is worth remembering that it is not just orbital disease processes that cause proptosis.
Exophthalmos also describes f...
Prussak space is a subcomponent of the lateral epitympanic space and extends from the level of the scutum to the umbo. This space is best demonstrated on the oblique coronal image.
lateral: pars flaccida of the tympanic membrane
medial: neck of the malleus
Psammoma bodies are round microscopic calcific collections. It is a form of dystrophic calcification. Necrotic cells forms the focus for surrounding calcific deposition. They have a lammelated concentric calcified structure, sometimes large enough to be seen on CT.
Psammoma bodies are found in...
The pterion is the H-shaped formation of sutures on the side of the calvarium representing the junction of four skull bones:
the greater wing of the sphenoid bone
squamous portion of the temporal bone
It is located at the the anterior end of the parietomastoid sut...
The pterygoid canal, also known as the Vidian canal, is a foramen in the base of skull, located in the sphenoid bone, inferomedial to the foramen rotundum. It transmits the Vidian artery and Vidian nerve from the middle cranial fossa to the pterygopalatine fossa.
It is an important structure a...
The pterygoid fovea is a small depression on the antromedial surface of the condylar process of the mandible marking the attachement of the inferior belly of the lateral pterygoid muscle.
The pterygomaxillary fissure is a triangular shaped lateral opening of pterygopalatine fossa.
It is located in the medial aspect of the temporal fossa and is formed by the divergence of maxilla from the pterygoid process of the sphenoid bone. It connects the infratemporal fossa w...
The pterygopalatine fossa (PPF) is a small space of the deep face the shape of an inverted pyramid between the maxillary bone anteriorly, the pterygoid process posteriorly and lies inferior to the orbital apex. It is quite important as it is a neurovascular crossroad of the nasal cavity, mastica...
The pterygopalatine ganglion is one of four parasympathetic ganglia of the head and neck and largest of the peripheral parasympathetic ganglia. The others include the ciliary ganglion, submandibular ganglion and the otic ganglion.
located in the pterygopalatine fossa
Pulsatile exophthalmos or pulsatile proptosis is a clinical symptom characterized by protrusion and pulsation of the eyeball that can occur due to various causes:
neurofibromatosis type 1 (with sphenoid wing dysplasia)
trauma (orbital roo...
The clinical symptom of pulsatile tinnitus can occur from a number of causes. They include
dehiscent jugular bulb
high riding jugular bulb
laterally placed sigmoid sinus
abnormal mastoid emissary veins
aberrant internal carotid ...
Punctum nervosum, also known as Erb’s point or the nerve point of the neck, is a point half way along the posterior border of the sternocleidomastoid muscle from which all cutaneous branches of the cervical plexus exit to become superficial.
The punctum nervosum is located on the...
The pyramidal lobe of thyroid is a normal variant. It is seen as a third thyroid lobe and is present in 10-30% of the population. It is likely related to a remnant of the thyroglossal duct. It usually arises from the isthmus upwards along the midline or is shifted towards the left of the neck, a...
The pyriform aperture, is a pear-shaped, bony inlet of the nose, is formed by the nasal and maxillary bones. The maxillary spines mark the inferior margin of the pyriform aperture.
pyriform aperture stenosis
Pyriform aperture stenosis refers to narrowing of the pyriform aperture and results from early fusion and hypertrophy of the medial nasal processes.
Pyriform aperture stenosis is a rare cause of airway obstruction, and its prevalence is unknown.