Tuesday, September 13, 2016

CAP16 Abstract Highlights -- Pilocytic Astrocytoma: A Diagnostic Consideration in Lateral Ventricular Tumors

The 2016 annual meeting of the College of American Pathlologists (CAP16) is coming up September 25-28 in Las Vegas. I'll be attending the meeting this year. In this series of posts, I'll be featuring poster abstracts of particular interest to neuropathologists.

Caleb Graham and colleagues at the University of Colorado (Poster #193) discuss the differential diagnosis of oligodendroglioma mimickers in the lateral ventricles. Here's the updated abstract:

Context: The most common lateral ventricular tumors are choroid plexus papilloma and meningioma, with a fewer number of cases of subependymoma, subependymal giant cell astrocytoma, lymphoma, and metastasis. Lateral ventricular pilocytic astrocytomas (PAs) are uncommon, seldom reported as a series, and must be excluded from neurocytoma and glioneuronal tumors.

Design: Our brain tumor databases were reviewed to identify all lateral ventricular PAs seen from 2000 to 2016. Magnetic resonance imaging studies were reviewed to exclude cases that were primarily parenchymal with secondary protrusion into the lateral ventricles. Immunohistochemical workup for glial and neuronal markers, as well as BRAF VE1 (surrogate marker for BRAF V600E mutation), were undertaken. KIAA:BRAF fusion status and electron microscopy were performed in 2 cases. 

Results: Four cases (ages 13, 21, 28, and 43 years) were identified. By neuroimaging 2 cases displaced the septum (Figure 75, A) and 1 was near the trigone (Figure 75, B). These cases had generated wide radiologic differential diagnoses, especially central neurocytoma in the 2 cases displacing the septum. Histologically, 3 of the 4 were predominantly composed of small round cells with perinuclear halos (Figure 75,C) and showed few piloid areas or Rosenthal fibers. These cases also showed patchy synaptophysin immunohistochemical positivity, traditionally associated with neuronal tumors (Figure 75, D), but those evaluated by electron microscopy failed to show neuronal lineage.Unlike typical gangliogliomas, all 4 were BRAF VE1 negative.

Conclusions: Lateral ventricle PAs are uncommon but should be considered when encountering lateral ventricular tumors.

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