The wart-like mass on the abdominal skin of a Pekinese was 2 mm in diameter, well-circumscribed, and purple to red 

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... are benign tumours of the vas- cular endothelium and are relatively common in dogs, but rare in other domestic animals. In dogs, haemangiomas occupy 2–3% of skin and usually arise on the leg, flank, neck, face, and eyelid (Vala and Esteves 2001; Meuten 2002). Angiokeratoma is an uncommon variant of der- mal haemangioma and has both a vascular and epi- thelial component. An angiokeratoma is a small, well-circumscribed, elevated dermal mass with histological characteristics of benign proliferations of dilated thin-walled blood vessels in the upper dermis with overlying epidermal hyperplasia that appears to have invaded the vascular component. Hyperkeratosis can also be observed (Yager and Wilcox 1994; Gross et al. 2005). This tumour type occurs most often on the eyelid and conjunctiva but can also arise in the superficial dermis at any site (Vala and Esteves 2001). Occasionally haemangioma, especially verrucous haemangioma which is a structural variant of capillary or cavernous haemangioma has similar macroscopic features to angiokeratoma, although the histologi- cal appearance and clinical behaviour are different. Therefore, distinguishing these lesions is important in histological study (Imperial and Helwig 1967). In human haemangioma cases, several studies have suggested that angiokeratoma, in particular angioker- atoma corporis diffusum, should raise the suspicion of various lysosomal storage diseases such as Anderson- Fabry’s disease, β-galactosidosis, fucosidosis, aspar- tylglucosaminuria, galactosialidosis, β-mannosidosis and Schindler/Kanzaki disease (Ozdemir et al. 2004). Lysosomal storage diseases are inherited meta- bolic disorders that result from an enzymatic de- ficiency within the lysosomal catabolic pathway (Skelly and Franklin 2002). The lysosome contains more than 60 kinds of acid hydrolases and a defi- ciency in these enzymes results in excessive storage of their substrates, leading to progressive cell damage and organ dysfunction (Nagayasu et al. 2008). Thus, electron-dense lysosomal deposits or electron-lucent lysosomal vacuoles are observed depending on the accumulated substrates (Kanda et al. 2002; Kanitakis et al. 2005; Molho-Pessach et al. 2007; Albano et al. 2010). Herein, we report the histopathologic and ul- trastructural analysis of an angiokeratoma char- acterised by miscellaneous benign hypervascular lesions accompanying lysosomal dilatation in the epidermal collarette. A six-year-old spayed female, Pekinese dog was presented to the veterinary clinic with two masses on the axillary and abdominal skin without any other significant signs. The dog had a history of continuous intervertebral disc disease since four years of age and auricular haematoma. General physical examination revealed two ery- thematous papules that were 2–3 mm in diameter, ovoid in shape, well-circumscribed, and slightly el- evated above the skin surface on the axillary and abdominal region (Figure 1). The masses were surgically removed, fixed in 10% neutral buffered formalin (BBC; Mount Vernon, WA, USA) and embedded in paraffin for light microscopic evaluation. The paraffin-embedded tissue was sec- tioned at 4 μm, and stained with haematoxylin and eosin formalin (BBC; Mount Vernon, WA, USA). For ultrastructural analysis, a piece of the mass (1 × 1 × 1 mm in dimension) was fixed in 2.5% glutaralde- hyde (Sigma-Aldrich; St. Louis, MO, USA) at 4 °C for 24 h. The samples were then post-fixed in osmium tetroxide (OsO 4 ; Merck, Darmstadt, Germany), dehydrated and embedded in Epon-812 (Electron microscopy sciences; Hatfield, PA, USA). Semi- thin sections were stained with 2% toluidine blue and examined to locate areas of interest within the block. Ultrathin sections were cut using an Ultracut E microtome (Reichert-Jung; Depew, NY, USA) and stained with 1.0% uranyl acetate and 1.0% lead cit- rate. Transmission electron microscope (TEM) (H- 7650; Hitachi, Ontario, Canada) examination was performed with a standard square mesh (GG200-Ni; Electron microscopy sciences) for calibration. Microscopic examination revealed both the axillary and abdominal masses to be well-cir- cumscribed, ulcerated, and exophytic nodules consisting of irregular hyperplasia of the over- lying epidermis with hyperkeratosis (Figure 2). The superficial corium was thickened by dilated, blood-filled vascular spaces identical to those in cavernous haemangioma. Beneath the nodule, the dermal layer showed oedematous collagen connec- tive tissue and compressed skin adnexal structures (Figure 2). Hyperplastic epithelium with spongiosis invaded the vascular component and partially sur- rounded the vascular structures (Figure 3). The axillary mass was identical to the abdominal mass with hyperplasia of overlying epidermis and vascular spaces in the superficial corium. Because of the identical nature of the two masses, only the abdominal mass was selected for electron microscopic examination. TEM showed cytoplasmic vacuoles within the keratinocytes that had invaded the vascular spaces. The vacuoles were electron-lucent and limited by a single membrane (Figure 4). In summary, in the presented dog axillary and ab- dominal lesions were diagnosed as angiokeratoma of the skin. In addition, the presence of electron- lucent lysosomal dilatation raised the possibility of concomitant lysosomal storage disease. This report describes a case of angiokeratoma with suspicion of lysosomal storage disease in a dog. Angiokeratoma is a rare variant of dermal haemangioma. Generally, haemangiomas are classified as being of the capillary or cavernous type depending on the size of the vascular spaces and the amount of inter- vening fibrous tissue (Scott et al. 2001). Verrucous haemangioma, a structural variant of capillary and cavernous haemangioma, has similar macroscopic and clinical features to angiokeratoma, with epider- mal acanthosis, papillomatosis, and hyperkeratosis developing secondarily. However, angiokeratoma in- volves only the papillary dermis and is located directly under the hyperplastic epidermis, whereas verrucous haemangioma involves the dermis and subcutaneous fat (Imperial and Helwig 1967). Therefore, not only the characteristics of cellular components, such as epidermal hyperplasia, hyperkeratosis, and dilated vessels and a surrounding of fine stroma, but also the structural characteristics of angiokeratoma, such as the location of the lesion, involvement of the dermis and subcutaneous tissue, and margins of the lesion, could be useful in the differential diagnosis of hae- mangioma variants (Imperial and Helwig 1967). An accurate diagnosis based on the histopathological fea- tures of the lesion is important for complete surgical excision, to make a prognosis and to predict possible complications (Mani and Feierabend 1982). There are several clinical variants of angiokera- tomas in humans. Local angiokeratoma comprises: 1. Angiokeratoma of Mibell; 2. Angiokeratoma of Fordyce; 3. Solitary and multiple popular angiokera- toma; 4. Angiokeratoma circumscriptum. Systemic angiokeratoma is described as angiokeratoma cor- poris diffusum, with widespread papules, and is a manifestation of one of several inherited lysosomal storage diseases such as Anderson-Fabry’s disease or fucosidosis (Ozdemir et al. 2004; Siponen et al. 2006). A correlation between lysosomal storage disease and angiokeratoma has been described in several studies on human subjects (Kanitakis et al. 2005; Molho-Pessach et al. 2007). According to a previous study, angiokeratoma corporis diffusum, which is a generalised systemic form that is usually associated with a metabolic disorder, was present in 52% of fucosidosis patients (Kanitakis et al. 2005). Because lysosomal storage disease is hereditary and has no definitive clinical or histological features, taking a family history for identification of genetic factors is important. However, it is difficult to obtain the fam- ily ...