Intracranial teratoma

Intracranial teratomas are uncommon intracranial neoplasms, which can have a bewildering variety of components and thus a wide range of appearances.  TheyThey can be divided into two broad categories,  intraintra and extra-axial, which differ in epidemiology and clinical presentation.  Another method of classifying an intracranial teratoma is as mature, immature and mature with with malignant transformation.

Epidemiology

Although uncommon in the general population, they account for the largest proportion of fetal intracranial neoplasms ( 26 - 50(26-50% of fetal brain tumours ^3,6)

Clinical presentation

Clinical presentation varies according to whether they are intra- or extra-axial. 

Intra-axial 

Intra-axial teratomas, i.e. those located within the cerebral hemispheres, typically present either antenatally or in the newborn period. They are large tumours that increase head circumference and therefore often present with difficulty in child birth. They tend to more commonly occur supratentorially.

Extra-axial 

Extra axial teratomas usually present in childhood or early adulthood and are typically smaller. They most commonly arise in the pineal or suprasellar regions, and present due to mass effect: obstructive hydrocephalus due to impingement on the mid brain, Parinaud's syndrome, optic chiasm compression etc...

Pathology

Teratomas are considered intracranial germ cell tumours,  and are comprised of cells originating from at least two and usually all three embryonic layers: ectoderm, mesoderm and endoderm. The histological sub type may not necessarily determine the biological behaviour. 

Sometimes may be associated with elevated levels of:

• serum alpha feto protein (AFP)
• serum carcinoembryonic antigen (CEA)

Radiographic features

Intracranial teratomas are often seen as large lesions at presentation. 

Given their extremely variable histological components, imaging also tends to be heterogenous, with tumours typically demonstrating a mixture of tissue densities and signal intensity. Fat, if present is helpful in narrowing the differential.

CT

The majority of intracranial teratomas demonstrate at least some fat and some calcification, which is usually solid/"clump like" ^4,6. They usually have cystic and solid components, contributing to an irregular outline. Solid components demonstrate variable enhancement ⁴. 

MRI

• T1
  • hyperintense components due to fat and proteinaceous / lipid/lipid rich fluid
  • intermediate components of soft tissue
  • hypointense components due to calcification and blood products
• T1 C+ (Gd):) : solid soft tissue components show enhancement
• T2: : again mixed signal from differing components

Treatment and prognosis

Location and size determines prognosis. 

In intra-axial (fetal) cases, stillbirth occurs relatively frequently, and difficulty with vaginal delivery (if attempted) can occur due to enlarged cranial circumference ³. 

In extra-axial cases it largely depends on the size and location. Smaller lesions can be successfully resected with good prognosis. 

Differential diagnosis

A meaningful differential depends to a degree on location. 

• intra-axial
  • sPNET
  • atypical rhabdoid / teratoid tumour (ATRT): older age group
  • choroid plexus carcinoma
• extra-axial
  • intracranial lipoma: fatty components only
  • intracranial dermoid: more mature tissue
  • craniopharyngioma: particularly for suprasellar lesions
  • other pineal region tumours