Journal of Small Animal Practice • Vol 53 • January 2012 • © 2011 British Small Animal Veterinary Association 63

CASE REPORT

Journal of Small Animal Practice (2012) 53, 63–66DOI: 10.1111/j.1748-5827.2011.01145.x

Accepted: 12 September 2011; Published online: 28 November 2011

Intratesticular benign peripheral nerve sheath tumour in a ferret (Mustela putorius furo)M. Hohšteter, O. Smolec*, A. Gudan Kurilj, I.-C. Šoštaric-Zuckermann, I. Bata† and Ž. Grabarevic

Department of Veterinary Pathology and *Department of Surgery, Orthopaedics and Ophthalmology Clinic, Faculty of Veterinary Medicine, University of Zagreb, Croatia

†Zagreb Zoo, Zagreb, Croatia

A domestic ferret was submitted for sterilisation because of right testis enlargement. Oestradiol and

cortisol concentrations were within normal physiological ranges, but testosterone was below and

progesterone above normal. Microscopically, the right testis, with the exception of a small part of the

epididymis, was replaced with neoplastic tissue. The tumour was composed of streams and bundles of

closely packed spindle to ovoid cells forming whorls around collagen and capillaries, and separated by

a collagenous matrix. In some areas, cells were loosely arranged and separated by a pale myxomatous

matrix. The left testis showed atrophy. The majority of neoplastic cells expressed vimentin and S-100

protein, while expression of collagen IV was moderate and there was no expression of glial fibrillary

acid protein. On the basis of macroscopical and histopathological findings, and supported by immuno-

histochemical reactivity, the diagnosis of benign peripheral nerve sheath tumour was made. This is the

first report of benign peripheral nerve sheath tumour in ferret testis.

INTRODUCTION

Peripheral nerve sheath tumours (PNSTs) are neoplasms aris-ing from Schwann cells, perineural cells and intraneural fibro-blasts. On the basis of morphological features and assessment of benign versus malignt, they can be subdivided into schwannoma or benign PNST (previously called neurilemoma or neuri-noma), neurofibroma or malignant PNST (Schulman and others 2009). Due to their uncertain histiogenesis, PNSTs in veterinary medicine are divided into benign and malignant variants in the most recent edition of the WHO International Histological Classification of Tumours of Domestic Animals (Koestner and others 1999). There are few studies of the incidence of neopla-sia in ferrets (Brown 1997, Zeeland and others 2006). The most common tumours reported are insulinoma, lymphoma and adre-nocortical neoplasms, followed by skin neoplasias and muscu-loeskeletal neoplasms (Dillberger and Altman 1989). Ovarian stromal tumours are the main neoplasia of the reproductive tract in female ferrets, while neoplasms of the male reproduc-tive system are unusual (Beach and Greenwood 1993). A few studies have described findings of testicular neoplasia in ferrets:

interstitial cell adenoma (Meschter 1989), Sertoli cell tumour in cryptorchid testis (Powers and others 2007) and mixed intersti-tial and Sertoli cell tumour (Batista-Arteaga and others 2011). In the available literature, there is only a single report of PNST in ferret, i.e. neurilemoma on the leg (Brown 1997). We now present the first case of benign PNST in a testicle of a ferret and discus in detail the reasons for this diagnosis.

CASE HISTORY

A 2·2 kg, male, 6-year-old, moderately obese domestic ferret from Zagreb Zoo was submitted to the Surgery, Orthopaedics and Ophthalmology Clinic, Faculty of Veterinary Medicine, University of Zagreb in October 2010 for sterilisation because of right testis enlargement. During the operation, blood samples were taken for determination of oestradiol, progesterone, testos-terone and cortisol concentrations. Ultrasound evaluation of the abdomen was performed before the orchidectomy, which was performed through a scrotal incision with ligation of the sper-matic cord, in the standard manner.

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The testes were submitted to the Department of Veterinary Pathology for histopathological examination. The left testis was round and about 0·8 cm in diameter (volume 0·27 cm3), while the right testis had a diameter of about 3·5 cm (volume 22·43 cm3). For comparison, the average testicular diameter in sexually mature ferrets is approximately 1·2 cm (Sisk 1990), with an aver-age volume of 0·94 to 1·38 cm3 (Schoemaker and others 2008). On the basis of these reported values, the left testis was slightly below the normal range but the right considerably above. The left testis was moderately firm and showed no macroscopic changes on the external or cut surface. The right testis was firm with a rugged, external surface and was whitish-grey and lobulated on the cut surface. The testes were fixed in 10% neutral buffered formalin, embedded in paraffin and processed routinely. Sections were stained by haematoxylin and eosin (H&E).

Immunohistochemistry was performed for exact tumour classification. Primary antibodies used were specific for the fol-lowing antigens: vimentin (VIM) (Clone V9, Dakocytomation, No. M0725, diluted 1:200), S-100 protein (S-100) (DakoCy-tomation, No. Z0311, diluted 1:400), glial fibrillary acid pro-tein (GFAP) (clone 6F2, DakoCytomation, No. M0761, diluted 1:300) and collagen IV (col IV) (clone CIV 22, DakoCytoma-tion, No. M0785, diluted 1:25). Antigen retrieval for S-100 was not performed and for VIM was performed at room tempera-ture with proteinase K (DakoCytomation, Code S3004) for 5 min. Antigen retrieval for col IV was performed with ethylene diamine tetraacetic acid (EDTA) buffer, pH 9 (DakoCytoma-tion, Code S2367) for 3×5 min, and for GFAP with citrate buffer pH 6 (DakoCytomation, Code S2031) for 20 min in a Dako PT Link module. Endogenous peroxidase activity was blocked by 5-min treatment with hydrogen peroxide (Dako No. S2023). Dako REAL EnVision Detection System, Peroxidase/DAB, Rab-bit/Mouse (No. K5007) was used to detect the antibodies against VIM, S-100, col IV and GFAP.

Standard electro-luminescence serum hormone testing showed an oestradiol concentration of 5·00 ng/L, progesterone of 18·6 nmol/L, testosterone of 0·087 nmol/L and cortisol of 40·8 nmol/L. Ultrasound examination of all abdominal organs, prostate and both adrenal glands (left=7·6 mm length, right=7·8 mm length) appeared normal [reference values reported by Neu-wirth and others (1997) left=8·6 ±1·2 mm; right=8·9 ±1·6 mm].

Microscopically, with the exception of a small part of epididy-mis, the remainder of the right testis was replaced with neoplas-tic tissue (Fig 1). The tunica albuginea was not penetrated by neoplastic cells. Neoplastic tissue was composed of interlacing streams and bundles of closely packed spindle to ovoid neoplas-tic cells and separated by small amounts of collagenous matrix. These cells often formed whorls around the collagen and capil-laries (Antoni A-like areas) (Fig 2). In some areas, cells were more loosely arranged and separated by a pale amphophilic, myxoma-tous matrix (Antoni B-like areas) (Fig 3). Borders of neoplastic cells were variably distinct and the cytoplasm was scant and eosinophilic. Nuclei varied from round to elongate with finely stippled, marginated or condensed chromatin, with one to two poorly distinct nucleoli. Mitotic figures were less than 1/10 per high-power fields. Areas of coagulative necrosis and haemorrhage

FIG 1. Right testis. With the exception of a small part of the epididi-mis, the rest of the right testis was replaced with neoplastic tissue (H&E, ×10)

FIG 2. Right testis. Antoni A-like areas, neoplastic cells form whorls around collagen and capillaries (H&E, ×10)

FIG 3. Right testis. Antoni B-like areas, neoplastic cells loosely arranged and separated by a pale amphophilic, myxomatous matrix (H&E, ×10)

Journal of Small Animal Practice • Vol 53 • January 2012 • © 2011 British Small Animal Veterinary Association 65

Intratesticular benign PNST in a ferret

cell tumours and are in 100% of cases positive for VIM (Chijiwa and others 2004, Bergmann and others 2009). S-100 identifies Schwann cells and hence, most PNSTs express this molecule (Chijiwa and others 2004, Bergmann and others 2009). As Col IV is a basement membrane component of Schwann cells, PNSTs can also be positive to this antibody (Gaitero and others 2008). Finally, GFAB, which is a neuronal marker, may be variably expressed (around 67%) in PNSTs (Chijiwa and others 2004, Bergmann and others 2009). Spindle cell tumours which can have similar IHC reactivity are malignant PNSTs, rabdomyosar-coma and other tumours of vascular origin (Chijiwa and others 2004, Bergmann and others 2009). In our case, typical histo-logical findings excluded potential diagnosis of these tumours. Morover, IHC reactivity to VIM, S-100 and col IV confirmed the diagnosis of benign PNST (Koestner and Higgins 2002, Chan and others 2007, Gaitero and others 2008, Schulman and others 2009).

were scattered throughout the tumour. The left testis showed marked atrophy. All of the aforementioned microscopic features, except for necrosis and haemorrhage, suggested a benign neo-plasm. Furthermore, the shape of the cells and their arrange-ment clearly indicated a neoplasm from the group of spindle cell tumours. The two different patterns with typical Antoni A- and Antoni B-like areas with the accompanying histological features are characteristic of benign PNST (Chijiwa and others 2004, Bergmann and others 2009). Although there were areas of coagu-lative necrosis and haemorrhage within the tumour, there were no other histological criteria of malignancy (infiltrative cell growth and aggressive behaviour, presence of atypical mononuclear or multinucleated cells, cellular pleomorphism, high mitotic index) to make a diagnosis of malignant PNST (Chijiwa and others 2004). Finally, even though histological features of the tumour were clearly suggestive of benign PNST, to exclude other spindle cell tumours, immunohistochemistry stains for VIM, S-100 and col IV were applied.

IHC staining for VIM was strongly positive in cytoplasm (Fig 4) and S-100 was moderately positive in the nuclei and cyto-plasm of majority of neoplastic cells (Fig 5). Col IV was moder-ately extracellularly positive (Fig 6), whereas staining for GFAB was negative in the tumour.

DISCUSSION

To our knowledge, this is the second report of a benign PNST in a domestic ferret and first report of this tumour in the tes-tis (Brown 1997). The diagnosis of benign PNST was based on macroscopic and histopathological findings which were identical to those described in the literature (Rothwell and others 1986, Koestner and Higgins 2002, Chijiwa and others 2004, Chan and others 2007, Bergmann and others 2009). As there is no single specific IHC marker that is able to define PNST, a panel of reagents is generally employed. PNSTs are mesenchymal spindle

FIG 4. Right testis. Neoplastic cells with strong cytoplasmic staining for vimentin (VIM) (IHC, ×40)

FIG 5. Right testis. Neoplastic cells are moderately positive in nuclei and cytoplasm for S-100 protein (S-100) (IHC, ×40)

FIG 6. Right testis. A moderate extracellular collagen IV (col IV) positive reaction (IHC, ×20)

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Oestradiol and cortisol concentrations were within the refer-ence ranges of 8 ±3 ng/L (Carroll and Baum 1989) and 53 ±42 nmol/L (Rosenthal and Peterson 1996), respectively. However, the progesterone concentration was approximately twice the normal value (3·1 ±0·42 ng/mL) (Carlson and Rust 1969) and the tes-tosterone concentration was more than 100 times lower than the normal value (9 to 73 nmol/l) (Schoemaker and others 2008).

As PNSTs are not hormone-secreting neoplasms, this raises some questions concerning the altered plasma concentrations of progesterone and testosterone. One explanation could be that progesterone is produced, in male animals, mainly by the adrenal glands and is then converted to testosterone in testes (Eckstein and others 1987, Maitra and Abbas 2005). Elevated progesterone and decreased testosterone levels could be the result of replace-ment of the testicular tissue of the right testis with neoplastic tissue and left testis atrophy. As a very small amount of functional testicular tissue remained, a very low conversion rate of proges-terone to testosterone could be assumed. As a result, testosterone concentrations would drop and progesterone concentration be increased in plasma.

Considering that surgical castration of male ferrets is a com-mon practice to prevent reproduction and to reduce interspecies aggression (Schoemaker and others 2008), it may be difficult to define the prevalence of testicular tumours in ferrets (Batista-Arteaga and others 2011). According to this, our finding of intra-testicular benign PNST can contribute to a better understanding of the incidence and clinic significance of testicular neoplasm in ferrets.

AcknowledgementsWe would like to thank Dr Marjana Coric, from the Department of Clinical Pathology, Zagreb Clinical Hospital Centre for con-ducting the immunohistochemical analysis.

This work was supported by Republic of Croatia, Ministry of Science, Education and Sports, project no. 053-053-2264-2260.

Conflict of interestNone of the authors of this article has a financial or personal relationship with other people or organisations that could inap-propriately influence or bias the content of the paper.

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