Choroid plexus carcinoma
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Choroid plexus carcinomas are malignant neoplasms arising from the choroid plexus. They are classified as a WHO grade 3 tumor and while there is considerable overlap in imaging characteristics they carry a significantly poorer prognosis than both WHO grade 2 atypical choroid plexus papilloma, and WHO grade 1 choroid plexus papilloma.
Choroid plexus carcinomas occur predominantly in children, typically in the first 5 years of life. They are rare, far less common than choroid plexus papillomas (which account for 80% of primary choroid plexus tumors), representing only 1-4% of pediatric brain tumors 5,7.
As is the case with choroid plexus papillomas, presentation is usually as a result of hydrocephalus. Symptoms include increasing head circumference and headaches. Papilledema may be visible on fundoscopy. In addition, choroid plexus carcinomas have a tendency to invade the adjacent brain and thus may present with focal neurological dysfunction 7,10.
simian virus 40 (SV40) on the basis of this virus' DNA having been identified in up to 50% of cases 5
Choroid plexus carcinomas are designated as WHO grade 3 tumors in the current (2021) WHO classification of CNS tumors 9. They originate from choroid plexus epithelium and typically arise de novo; rarely they may represent malignant transformation of a pre-existing choroid plexus papilloma 4.
Macroscopically, choroid plexus carcinomas are lobulated masses with cystic and necrotic areas.
It has been suggested that to make the diagnosis of choroid plexus carcinoma, at least 4 of the following 5 features should be present 8:
increased mitotic rate: >5 per 10 high-power fields
blurred papillary structure
Microcalcifications and hemorrhage may be present. Brain parenchymal invasion is a feature, and if present helps to distinguishes choroid plexus carcinomas from choroid plexus papillomas.
The immunophenotype of choroid plexus carcinomas is similar to that of choroid plexus papillomas, with both S11 and transthyretin more likely to be negative 8.
S100: often negative
transthyretin: often negative
p53 protein: positive in individuals with TP53 mutation
KIR7.1: only positive in ~50% of cases
The most common underlying genetic mechanism identified in their formation is dysfunction of the p53 tumor suppressor gene (TP53).
Choroid plexus carcinomas are markedly enhancing intraventricular tumors, usually arising in the trigone of a lateral ventricle and invading adjacent brain parenchyma.
Hydrocephalus may be present but is less likely than with choroid plexus papillomas. In choroid plexus carcinomas, hydrocephalus is generally a consequence of mechanical CSF pathway obstruction by the mass or CSF seeding, whereas, in choroid plexus papillomas, there is at least a component of CSF overproduction.
On non-contrast CT choroid plexus carcinomas are heterogeneous and typically iso to hyperdense to grey matter. Calcification may be seen in 20-25% of cases.
Contrast enhancement is usually prominent but heterogeneous with areas of necrosis and cyst formation evident.
Reported signal characteristics include
T1: iso- to hypointense
T2: iso- to hypointense with hyperintense necrotic areas
T2* GRE: blooming from calcifications/hemorrhage
T1 C+ (Gd): can show marked, heterogeneous enhancement.
The tumors may have CSF seeding, therefore imaging of the entire neural axis is recommended prior to surgery.
Treatment and prognosis
Choroid plexus carcinomas are rapidly growing tumors with a 40% 5-year survival. TP53 mutation, brain invasion and CSF seeding are considered poor prognostic factors 3-5.
Surgical en-bloc resection is the mainstay of treatment and can result in a cure, achieved in as many as 50% of cases, but this result has only been reported in some selected series 5. In general, survival seems to be much worse than this, and hinges upon the ability to achieve gross complete macroscopic resection. In such cases, a 5-year survival of up to 86% can be achieved. In cases where resection is incomplete, 5-year survival is much lower 26% 6. Both radiotherapy and chemotherapy are used 5.
General imaging differential considerations include:
generally difficult to categorically distinguish these on imaging alone, however some features are helpful:
lack of necrosis
lack of cerebral parenchymal invasion
older age favors choroid plexus papilloma
usually in the body of the lateral ventricle, typically abutting the septum pellucidum
more homogeneous outline and contrast enhancement
rare in children
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