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A 9-year-old male captive savannah monitor (Varanus exanthematicus) with a history of general debility was submitted for necropsy. Grossly, there were multiple white masses in the colon, mesorchium and tracheal adventitia. Histologically, the lesions were composed of epithelioid to spindloid neoplastic cells arranged in sheets to interlacing and interwoven bundles, and separated by abundant myxoid material or extensive stromal hyalinization and fibrosis with occasional chondroid metaplasia. Perivascular infiltration of epithelioid neoplastic cells was occasionally seen. Neoplastic cells were immunopositive for alpha-smooth muscle actin, melan-A and S100. The unique histological features and concurrent myogenic and melanocytic immunophenotypes suggest a malignant perivascular epithelioid cell tumour. To our knowledge, this is the first report of perivascular epithelioid cell tumours in a non-human species.

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Soft tissue sarcomas (STS) comprise a heterogeneous group of malignancies derived from extra-skeletal mesenchymal tissues that may show similar histopathological changes. Histopathologic patterns suggestive of perivascular wall tumors (PWT) and peripheral nerve sheath tumors (PNST) have been described. This study investigated the histogenesis in a series of 71 cases of canine STS that showed morphological compatibility with what is described for PWT and PNST. Immunohistochemistry analysis were done to CD56, S100, SMA, Desmin, Von Willebrand Factor, NSE and GFAP. Twenty-one cases (29.6%) showed histopathologic features compatible with PWT, 23 cases (32.4%) with PNST and 27 cases (38.0%) shared both histopathological features. By immunohistochemistry, 59 (83.1%) cases showed positivity only for neural markers and 12 (16.9%) had simultaneous positivity for both neural and muscle markers. PNST was the most prevalent neoplasm and none of the cases were positive for muscle markers only. The histopathologic features were not useful to define the diagnosis of PWT, since most tumors were negative for muscle markers but positive for neural markers. Due to this immunoreactivity and the morphologic features, future studies may propose guidelines for the classification of these neoplasms.(AU)

Sarcoma de tecidos moles (STM) compreende um grupo heterogêneo de neoplasias malignas, derivadas de tecidos extraesqueléticos, que podem apresentar alterações histopatológicas similares. Os padrões histopatológicos sugestivos de tumor de parede perivascular (TPP) e de tumor de bainha de nervo periférico (TBNP) têm sido descritos. Este estudo investigou a histogênese de uma série de 71 STM caninos, que apresentavam compatibilidade morfológica com o que é descrito para TPP e TBNP. A análise imuno-histoquímica foi feita para CD56, S100, SMA, Desmina, Fator Von Willebrand, NSE e GFAP. Vinte e um casos (29,6%) apresentaram características histopatológicas compatíveis com TPP, 23 casos (32,4%) com TBNP e 27 casos (38,0%) apresentaram características histopatológicas de ambos. Na imuno-histoquímica, 59 (83,1%) casos apresentaram positividade somente para marcadores neurais e 12 (16,9%) tiveram positividade simultânea tanto para marcadores neurais como para marcadores musculares. TBNP foi a neoplasia mais prevalente e nenhum dos casos foi positivo para somente para marcadores musculares. As características histopatológicas não foram úteis para definir o diagnóstico de TPP, uma vez que a maioria foi negativa para marcadores musculares, mas positiva para marcadores neurais. Devido a essa imunorreatividade e às características morfológicas, pesquisas futuras poderão propor orientações para a classificação dessas neoplasias.(AU)

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BACKGROUND: Hikui disease is a well known disfiguring disease of koi carp (Cyprinus carpio) primarily affecting fish with red pigmentation. It causes light orange to golden yellow, multifocal to coalescing raised patches, starting from the red cutaneous areas. Some cases respond to surgery or topical treatment, but recurrence is common. OBJECTIVES: To describe the clinical and pathological presentation of Hikui disease and its cause. ANIMALS: Nine affected koi carp belonging to private hobbyists. METHODS: Eight fish underwent surgery or biopsy; one was euthanized. Tissues were submitted for histology, immunohistochemistry and transmission electron microscopy. RESULTS: Five fish showed typical lesions of Hikui disease, whereas four fish showed an atypical presentation characterized by focal or multifocal, oedematous, dark red cutaneous plaques or nodules. Histology showed unencapsulated, infiltrating and densely cellular neoplasms composed of spindle cells arranged in bundles, rows and whorls frequently centred on capillaries. Immunohistochemistry for smooth muscle actin labelled neoplastic cells in all cases. Ultrastructure showed neoplastic cells with slender cytoplasmic processes encircling the capillaries, a thin basal membrane and occasional plasmalemmal vesicles. CONCLUSIONS AND CLINICAL IMPORTANCE: All of the data supported a neoplastic process producing perivascular wall tumours. Immunoreactivity to smooth muscle actin and the ultrastructural features were indicative of a pericyte origin (haemangiopericytoma). This is the first report dealing with Hikui disease that has achieved a conclusive diagnosis. The neoplastic nature of this condition suggests the potential usefulness of a surgical approach in the clinical management of less severe cases.

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Canine perivascular wall tumors (cPWTs) arise from vascular mural cells and are included among soft tissue sarcomas (STSs). Most prognostic studies are performed on canine STSs as a general group and regardless of their specific histotype. The aim of this study was to identify pathological parameters and profiles with prognostic impact for cutaneous/subcutaneous cPWTs. Anatomical location, type of growth, surgical margins, and size and depth of the tumor were collected in 56 cPWTs. The association between each pair of variables was evaluated by χ(2) test. Multiple correspondence analysis (MCA) was performed to describe the multivariate association of variables and was followed by cluster analysis to identify specific pathological profiles. The prognostic impact of variables and profiles was assessed by Cox regression model. Size and depth were significantly associated with increased relapse probability. Cases with complete surgical margins did not recur. Other single variables were not significantly associated with relapse. Cluster analysis on MCA considering site, depth, margins, and type of growth identified 3 pathological profiles associated with PWT relapse and having a high prognostic impact. Major prognostic factors for cPWTs were tumor size, depth of growth, and pathological profiles.

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Canine malignant peripheral nerve sheath tumors (MPNSTs) occur not only in the peripheral nervous system (PNS) but also in soft tissue and various organs (non-PNS). The most important diagnostic criterion is proof of peripheral nerve sheath origin. This is difficult in non-PNS MPNSTs, and its differential diagnosis is challenging. Canine perivascular wall tumors (PWTs) also commonly arise in soft tissue. Their histopathological features are quite similar to those of canine MPNSTs, making their differential diagnosis challenging. To elucidate whether the morphological features are applicable to diagnose non-PNS MPNSTs and to demonstrate useful markers for distinction between canine MPNSTs and PWTs, the authors examined 30 canine MPNSTs and 31 PWTs immunohistochemically for S100, nestin, NGFR, Olig2, claudin-1, CD57, PRX, α-SMA, desmin, and calponin. Among canine MPNSTs, the PNS tumors displayed significantly higher S100 and Olig2 expression than the non-PNS tumors. The expression levels of the other markers did not differ significantly, suggesting that the same morphological diagnostic criteria are applicable regardless of their location. The PWT cells displayed significantly weaker immunoreactivity than MPNSTs to markers used except α-SMA and desmin. Cluster analysis sorted most canine MPNSTs and PWTs into 2 distinctly different clusters, whereas 3 MPNSTs and 6 PWTs were assigned to the opposing cluster. These 3 MPNSTs were negative for almost all markers, while these 6 PWTs were positive for only neuronal markers. In particular, NGFR and Olig2 were almost negative in the rest of PWT cases. These findings suggest that NGFR and Olig2 are useful to distinguish these 2 tumors.

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