Choroid plexus papilloma

Choroid plexus papillomas are an uncommon, benign (WHO grade I) neuroepithelial intraventricular tumour, which can occur in both the paediatric (more common) and adult population. 

On imaging, these tumours are usually identified in the fourth ventricle in adults and in the lateral ventricles in the paediatric population. They commonly present as a solid vascular tumour with a vivid frond-like enhancement pattern. In a quarter of cases, speckled calcifications are present. 

Epidemiology

Overall, these tumours account for approximately 1% of all brain tumours, 2-6% of paediatric brain tumours and 0.5% of adult brain tumours. They are, however, disproportionately represented in brain tumours in children under the age of 1 ¹⁰. Approximately 85% of all choroid plexus papillomas occur in children under the age of 5 years ⁴.

Interestingly, the age distribution is very different for infratentorial (fourth ventricle) and supratentorial (usually lateral ventricle) tumours. The vast majority of supratentorial tumours are seen in children, whereas posterior fossa tumours are evenly distributed among all age groups, including the elderly ⁹.

Associations

An association with Aicardi syndrome and von Hippel-Lindau disease (as well as the more frequently associated haemangioblastoma) is recognised. 

Clinical presentation

Hydrocephalus is very common, seen in over 80% of cases ⁴. Although the exact mechanism remains uncertain, it is believed to be due to a combination of CSF overproduction and decreased arachnoid granulation resorption. 

Pathology

Choroid plexus papillomas are WHO grade I lesions. Their low mitotic rate (<2 mitoses are present per 10 high-power field) and, to a lesser degree, histological features distinguish them from atypical choroid plexus papillomas (WHO grade II) and choroid plexus carcinomas (WHO Grade III) ^7,10. 

Location

Unlike most other brain tumours, which are more common in the posterior fossa in children and supratentorial compartment in adults, the relationship is reversed for choroid plexus papillomas:

• adults: most often (70%) occur in the fourth ventricle
• children: most often occur in the lateral ventricles, with a predilection for the trigone

Third ventricular, cerebellopontine angle, parenchymal, and even pineal region tumours have also been described. 

Macroscopic appearance

Choroid plexus papillomas typically appear as cauliflower-like masses ^4,10. 

Microscopic appearance

These tumours demonstrate papillary structures with a delicate fibrovascular core lined by columnar or cuboidal epithelial cells with vesicular basal nuclei. Their appearance is very similar to normal choroid plexus ⁷.

Immunophenotype

• cytokeratins: positive (especially CK7)
• vimentin: positive
• transthyretin
  • usually positive
  • also found in normal choroid plexus
  • better prognosis if positive ¹⁰
• S100
  • variable
  • better prognosis if positive ¹⁰
• KIR7.1
  • usually positive and specific
  • potassium channel also found in normal choroid plexus ¹⁰

Radiographic features

On imaging, choroid plexus papillomas are characterised by vividly enhancing masses, usually intraventricular. Hydrocephalus is common. 

CT

The tumours are usually well-defined lobulated masses, either iso- or somewhat hyperdense compared to the adjacent brain. There is associated hydrocephalus. They usually homogeneously enhance, demonstrating an irregular frond-like pattern, resulting in a cauliflower-like appearance. If there is markedly heterogeneous contrast enhancement, a choroid plexus carcinoma should be suspected ⁴.

Fine, speckled calcification is seen within the tumour in approximately 25% of cases ⁴. 

MRI

The frond-like morphology of the tumour can usually be seen, especially following contrast administration. Varying degrees of associated hydrocephalus are also present in almost all cases.

• T1: typically isointense compared to adjacent brain; may be somewhat hypointense
• T2
  • iso to hyperintense
  • small flow-voids may be seen within the tumour
• T1 C+ (Gd): marked enhancement, tends to be homogeneous
• MR spectroscopy
  • decreased NAA
  • increased Cho

Angiography

Being very vascular tumours, these masses demonstrate intense vascular blush on angiography. Enlarged choroidal arteries may be seen feeding the tumour, with shunting ⁴.

Treatment and prognosis

Total excision should be the aim of therapy and is curative in a vast majority of cases. Overall, there is 90% 1-year-survival, and 77% 5-year-survival ¹⁰. 

CSF seeding is uncommon in choroid plexus papillomas, but far more frequently seen in higher-grade tumours such as atypical choroid plexus papillomas and choroid plexus carcinomas ¹⁰. 

Differential diagnosis

The differential is essentially that of other choroid plexus tumours:

• atypical choroid plexus papilloma: indistinguishable, but far less common
• choroid plexus carcinoma: can be very difficult on imaging alone
  • almost exclusively found in young children ⁷
  • heterogeneous contrast enhancement
  • may show parenchymal invasion
• choroid plexus metastases

When located in the posterior fossa in children (less common) other tumours to be considered include:

• medulloblastoma
• atypical teratoid/rhabdoid tumour (AT/RT) 
• ependymoma

In adults, and depending on location, consider:

• ependymoma
• intraventricular meningioma
• subependymoma  
• central neurocytoma
• exophytic glioma