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Choroid plexus neoplasms

CHOROID PLEXUS NEOPLASMS

The choroid plexus (CP) is a specialized epithelium that secretes cerebrospinal fluid (CSF) and is sited in the ventricles of the brain. Most neoplasms of CP are papillomas (CPPs), but some show an increased mitotic count, often in combination with atypical architectural and cytological features (atypical CPPs), or the histologic and behavioral characteristics of carcinomas (CPCs). Atypical CPPs represent approximately 15% of CPPs. CPCs are rare, and mostly occur in children. In the latest edition of the WHO classification (2007), the CPP corresponds to WHO grade I, the atypical CPP to WHO grade II, and the CPC to WHO grade III.

MACROSCOPIC APPEARANCES

CPPs are well-circumscribed neoplasms with a stippled surface that reflects their papillary structure (Fig. 40.1). In contrast, CPCs tend to invade local structures. Both types of neoplasm can be highly vascular, and CPCs frequently contain foci of hemorrhage (Fig. 40.2).

40.1 CPP.
The cerebellopontine angle is an unusual site for a CPP; nearly all are intraventricular. A stippled surface resembling that of a cauliflower is evident.

40.2 CPC.
A large, hemorrhagic mass fills the ventricles.

CHOROID PLEXUS NEOPLASMS

 Constitute approximately 0.5% of CNS neoplasms, approximately 3% of childhood CNS neoplasms, and may be congenital.

 Occur over a wide age range, but over 50% are present before 2 years of age.

 Are generally in the lateral ventricles in children.

 Are predominantly in the fourth ventricle in adults.

 Are frequently associated with hydrocephalus due to blocked CSF drainage pathways ± increased CSF production.

GENETIC FACTORS AND CP NEOPLASMS

 CPP occasionally occurs in patients with Aicardi syndrome (agenesis of the corpus callosum/infantile spasms/chorioretinal lacunae).

 CPC have been reported in members of families with Li-Fraumeni syndrome (germline mutation of TP53). However, TP53 mutations are rare in CP neoplasms.

 CP neoplasms are induced in transgenic mice by the large T antigen of simian virus 40. However, the presence of this virus in a proportion of human CP neoplasms (and other CNS neoplasms) is probably related to contamination of a polio vaccine with this virus; the phenomenon is only found in patients from countries that used contaminated vaccine.

 CPP and CPC show multiple cytogenetic losses and gains of chromosome arms. In CPC, longer survival is associated with loss of 10q and gain of 9p.

MICROSCOPIC APPEARANCES

CPPs resemble normal CP, being characterized by a columnar epithelium that rests on a delicate fibrovascular network and forms multiple papillary projections (Figs 40.3, 40.4). However, CPPs can be distinguished from CP because they demonstrate minor atypical cytologic features, such as:

40.3 CPP.
(a) In many areas, an obvious papillary architecture is found. A more complex pattern may be present in atypical CPPs (b) but this and superficial invasion of the stroma (arrow) do not warrant a diagnosis of CPC.

40.4 CPP.
(a) A layer of cuboidal or columnar cells rests on a fibrovascular stroma. (b,c) In addition to architectural abnormalities, mild cytological atypia and occasional mitoses distinguish the CPP from CP. (d) Immunoreactivity for cytokeratins is a feature of CP tumors. (e) Kir7.1 antibodies label the membrane of epithelial cells in CP neoplasms. (f) Rare CPPs contain oncocytic cells, or (g) melanin.

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