Craniopharyngioma (historical)

Craniopharyngiomas are relatively benign (WHO grade I) neoplasms that typically arise in the sellar/suprasellar region. They account for ~1-5% of primary brain tumours, and can occur anywhere along the infundibulum (from the 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 ^4-5,5. They are:

• adamantinomatous (paediatric): ~90 % ⁹
• papillary (adult): ~10 % ⁹
• mixed: ~15%, but share imaging and prognosis similar to adamantinomatous ⁴

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 smaller peak in adults aged over 50 years old, comprised mostly of papillary subtype ^4-5-9,5,9. 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 cleft rather than squamous cell crests along the craniopharyngeal duct as was previously thought ³. This histological appearance of the two subtypes are different, accounting for the various imaging features. 

Adamantinomatous

This type is seen predominantly in children. It consists of reticular epithelial cells that 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 subtype 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 ^3-4,4.

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 large 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 the 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 subtype). The third ventricle is a particularly common location. 

Rare or ectopic locations reported include: nasopharynx, posterior fossa, extension down the cervical spine.

Adamantinomatous

Adamantinomatous craniopharyngiomas is the most common form ~ 90%,  and typically have a lobulated contour as a result of usually multiple cystic lesions. Solid components are present, but often form a relatively minor part 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 tumours 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
  • near CSF density
  • typically large and a dominant feature
  • present 90 % of the time
• solid component
  • soft tissue density
  • enhancement in 90%
• calcification
  • seen in 90%
  • typically stippled and often peripheral in location

MRI 

• cysts
  • T1: iso- to hyperintense to brain (due to high protein content "machinery oil cysts")
  • T2: variable but ~80% are mostly or partly T2 hyperintense
• solid component
  • T1 C+ (Gd): vivid enhancement
  • T2: variable or mixed 
• calcification
  • difficult to appreciate on conventional imaging
  • susceptible sequences may better demonstrate calcification
• MR angiography: may show displacement of the A1 segment of the anterior cerebral artery (ACA)
• 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 significant feature
  • near CSF density
• solid component
  • soft tissue density
  • vivid enhancement
• calcification
  • uncommon, rare

MRI 

• cysts
  • when present they are variable in signal
  • T1: 85% T1 hypointense ⁴
• solid component
  • T1: iso- to slightly hypointense to brain
  • T1 C+ (Gd): 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 aggressive biological nature ⁴. 

History and etymology

Craniopharyngiomas have also been known as pituitary ameloblastomas - there are no specific histological features to separate them from mandibular ameloblastomas ⁸. 

Differential diagnosis

General imaging differential considerations include:

• Rathke cleft cyst
  • no solid or enhancing component
  • calcification is rare
  • unilocular
  • the majority are completely or mostly intrasellar 
• pituitary macroadenoma (with cystic degeneration or necrosis)
  • can look very similar
  • usually has intrasellar epicentre with pituitary fossa enlargement rather than suprasellar epicentre
  • despite occasional presence of T1 bright cystic regions, calcification in these cases is often absent (whereas most adamantinomatous craniopharyngiomas are calcified)
• intracranial teratoma
  • presence of fat is helpful, but requires fat saturated sequences or CT to confirm

See also

• differential for a suprasellar mass