Use of Electron Microscopy to Classify Canine Perivascular Wall Tumors

Abstract

The histologic classification of canine perivascular wall tumors (PWTs) is controversial. Many PWTs are still classified as hemangiopericytomas (HEPs), and the distinction from peripheral nerve sheath tumors (PNSTs) is still under debate. A recent histologic classification of canine soft tissue sarcomas included most histologic types of PWT but omitted those that were termed undifferentiated. Twelve cases of undifferentiated canine PWTs were evaluated by transmission electron microscopy. The ultrastructural findings supported a perivascular wall origin for all cases with 4 categories of differentiation: myopericytic (n = 4), myofibroblastic (n = 1), fibroblastic (n = 2), and undifferentiated (n = 5). A PNST was considered unlikely in each case based on immunohistochemical expression of desmin and/or the lack of typical ultrastructural features, such as basal lamina. Electron microscopy was pivotal for the subclassification of canine PWTs, and the results support the hypothesis that canine PWTs represent a continuum paralleling the phenotypic plasticity of vascular mural cells. The hypothesis that a subgroup of PWTs could arise from a pluripotent mesenchymal perivascular wall cell was also considered and may explain the diverse differentiation of canine PWTs.

Reclassification of 21 Presumptive Canine Peripheral Nerve Sheath Tumors (PNST) Using a Literature-Based Immunohistochemical Panel

“…According to recent studies a small subgroup of PWTs with equivocal morphology and lack of specifi c immunohistochemical markers may exist, so that in the case of extensive immunohistochemical negativity a defi nitive diagnosis may not be reached. In order to provide clarity, further IHC studies should be performed in the presence of a defi nitive diagnosis based on ultrastructural investigation [29].…”

Canine Perivascular Wall Tumors

“…1 Immunohistochemical and ultrastructural studies of PNSTs and cPWTs have respectively confirmed the perineural and perivascular origin of tumors indentified by the aforementioned growth models and have allowed their specific subtyping. 1,10,26,30 Hence, cPWTs have been subclassified into hemangiopericytomas, myopericytomas, angioleiomyomas/ sarcomas, angiofibromas, and adventitial tumors, 1 while PNSTs have been subtyped into schwannomas and neurofibromas. 10,15,30 Of the latter, several histological variants have been described.…”

Metastatic intraocular hemangiopericytoma in a dog

“…If the pseudocapsule is breached during surgery or incomplete excision is noted, extensive local regrowth and metastasis can be seen (Shimura et al, 2001). Proper diagnosis of hemangiopericytomas can be challenging from a histopathologic standpoint and recent investigations show that many previous cases diagnosed as such may actually represent one of a spectrum of perivascular wall tumors (Avallone et al, 2007;Palmieri et al, 2013). The originally described microscopic pattern of a hemangiopericytoma consisted of concentric layers of spindle cells arranged http://www.openveterinaryjournal.com J.D.…”