Craniopharyngiomas are relatively benign (WHO grade I) neoplasms which typically arise in the sellar / suprasellar region. They account for ~ 1 - 5% of primary brain tumours, and can occur anywhere along the infundibulum (from floor of the third ventricle, to the pituitary gland).
There are two pathological types, which are said to differ not only in appearances, but also in prognosis and epidemiology. Whether or not they represent distinct entities or a spectrum of morphology remains a little controversial 4-5. They are:
adamantinomatous (paediatric)
papillary (adult)
mixed: ~ 15%, but share imaging and prognosis similar to adamantinomatous4
Epidemiology
Although craniopharyngiomas are found in patients of all ages there is a bimodal distribution, with the first peak between the ages of 10 - 14 years, made up almost exclusively of adamantinomatous type, and a second peak in young to middle-aged adults, comprised mostly of papillary subtype 4-5. There appears to be a similar incidence in both males and females 3.
Clinical presentation
Clinical presentation is variable on account of the variable location and size of the tumour. Presenting complaints include :
headaches and raised ICP
visual symptoms
20% of children 3
80% adults
hormonal imbalances
short stature and delayed puberty in children
decreased libido
amenorrhoea
diabetes insipidus
behavioural change due to frontal or temporal extension
Pathology
Craniopharyngiomas are believed to derive from Rathke's cleft rather than squameous cell rests along the craniopharyngeal duct as was previously thought3. This histological appearances of the two subtypes are different, accounting for the different imaging features.
Adamantinomatous
This type is seen predominantly in children. It consists of reticular epithelial cells which have appearances reminiscent of the enamel pulp of developing teeth.
There may be single or multiple cysts filled with thick oily fluid high in protein, blood products, and/or cholesterol, creating the so called "machinery oil". "Wet keratin nodules" are a characteristic histological feature. Calcification is usually present : ~ 90% 3.
Papillary
The papillary sub type is seen almost exclusively in adults and is formed of masses of metaplastic squamous cells 3. "Wet keratin" is absent. Cysts do form, but these are less of a feature, and the tumour is more solid. Calcification is uncommon or even rare 3-4.
Radiographic features
Although similar in terms of location, radiographic features depend on the type, although due to a significant minority of tumour having both adamantinomatous and papillary components many show overlapping features.
Location
In the vast majority of cases, craniopharyngiomas have a significant suprasellar component (95%), with most involving both the suprasellar and intrasellar spaces (75%). A minority are purely suprasellar (20%), whereas purely intrasellar location is quite uncommon (<5%), and may be associated with expansion of the pituitary fossa 3,7. Larger tumours can extend in all directions, frequently distorting the optic chiasm, or compressing the midbrain with resulting obstructive hydrocephalus.
Occasionally, craniopharyngiomas appear as intraventricular, homogeneous, soft-tissue masses without calcification (papillary sub type). The third ventricle is a particularly common location.
Rare / ectopic locations reported include: nasopharynx, posterior fossa, extension down the cervical spine.
Adamantinomatous
Typically adamantinomatous craniopharyngiomas have a lobulated contour as a result of usually multiple cystic lesions. Solid components are present, but usually form a relatively minor component of the mass, and enhance vividly on both CT and MRI. Overall, calcification is very common, but this is only true of the adamantinomatous subtype (90% are calcified) 4.
These tumour have a predilection to be large, extending superiorly into the third ventricle, and encasing vessels, and even being adherent to adjacent structures 4.
CT
cysts
typically large and a dominant feature
near CSF density
solid component
soft tissue density
vivid enhancement
calcification
seen in 90%
typically stippled and often peripheral in location
MRI
cysts: variable but ~80% are mostly or partly T2 hyperintense
solid component
T1: iso to lightly hypointense to brain
T1 C+: vivid enhancement
T2: variable / mixed
calcification
difficult to appreciate on conventional imaging
susceptible sequences may better demonstrate calcification
MR angiography: may demonstrate displacement of the A1 segment of the anterior cerebral artery
MR spectroscopy: cyst contents may show a broad lipid spectrum, with an otherwise flat baseline 6
Papillary
Papillary craniopharyngiomas tend to be more spherical in outline and usually lack the prominent cystic component; most are either solid or contain a few smaller cysts. Calcification is uncommon or even rare in the papillary subtype, a fact often forgotten 4.
These tumours tend to displace adjacent structures.
CT
cysts
small and not a major feature
near CSF density
solid component
soft tissue density
vivid enhancement
calcification
uncommon - rare
MRI
cysts
when present they are variable in signal
85% T1 hypointense 4
solid component
T1: iso to lightly hypointense to brain
T1 C+: vivid enhancement
T2: variable / mixed
MR spectroscopy: cyst contents does not show a broad lipid spectrum as they are filled with water fluid
Treatment and prognosis
Treatment is usually surgical with radiotherapy especially useful for incomplete resection. Surgical approach depends on the size and sellar vs suprasellar extent. Some lesions can be accessed via a transphenoidal approach, whereas others require a craniotomy.
Benign local recurrence is seen in up to a third of patients 3 and is said to significantly depend on histology: papillary has a much lower recurrence rate than adamantinomatous, although this may merely represent the more extensive and adherent character of the latter rather than an intrinsically more agressive biological nature 4.
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