DOI: 10.1002/vms3.543 CASE REPORT Diagnostic imaging and pathological findings of an abdominal mesenteric granular cell tumour in a dog Alejandro Ororbia1 | Alba Sanz2 | Rosa Novellas1,2 | Josep Pastor1,2 | Marti Pumarola2,3 | Laura Fresno2 | Yvonne Espada1,2 1 Fundació Hospital Clinic Veterinari, Universitat Autònoma de Barcelona, Abstract Barcelona, Spain A 12-year-old mixed-breed dog was presented for a follow-up examination after 2 Departamento de medicina y cirugía ablation of an auricular mast cell tumour. An abdominal ultrasound and computed animal, Universitat Autònoma de Barcelona, Barcelona, Spain tomography were performed and an irregular, ill-defined and partially mineralised 3 Unit of Murine and Comparative Pathology lesion was observed around the caudal duodenal flexure without evidence of me- (UPMiC) and Networking Research Center on Bioengineering, Biomaterials and tastasis. The cytologic examination was highly suggestive of a granular cell tumour. Nanomedicine (CIBER-BBN), Barcelona, Partial surgical ablation with histological and immunohistochemical examination of Spain the lesion confirmed the diagnosis. According to our review of the literature, this is Correspondence the first report documenting an abdominal granular cell tumour in a dog. Alejandro Ororbia, 23 West bank road, Allestree, Derby DE22 2FY, UK. KEYWORDS Email: aoaranguren@gmail.com canine, duodenum, fat, intestine, myoblastoma, veterinary 1 | I NTRO D U C TI O N II mast cell tumour. At presentation, the patient was bright, alert and responsive. All vital parameters were within normal limits. The Granular cell tumours, once called granular cell myoblastomas, are owner did not report any gastrointestinal signs. uncommon and usually benign lesions in both human and veterinary A complete blood cell count, serum biochemistry and abdominal medicine. The oral cavity (notably the tongue) is the most common ultrasound were performed as part of the oncologic examination. location in dogs, cats and people, but a wide range of other locations Mild normocytic, normochromic, non-regenerative anaemia [RBC have been described (Higgins et al., 2017; Levitin et al., 2019; Mobarki 5.84 × 106/μl (5.5–8.5), Hb 13.7 g/dl (12–18), PCV 36% (37–55), re- et al., 2020; Patnaik, 1993). In dogs, documented locations for this ticulocytes 19,856 (0–60,000)] and moderate increase of alkaline type of tumour include the brain, meninges, spinal nerve root, heart, phosphatase [1356.5 UI/L (20–156)] were detected. Otherwise, the lung, eye, vocal cord and trachea (Levitin et al., 2019; Patnaik, 1993). blood work was unremarkable. According to our review of the literature, there is not a previous publi- On the abdominal ultrasound an irregular and elongated lesion cation of an abdominal granular cell tumour in the dog. with ill-defined margins was observed in the mesentery adjacent to the serosa of a small intestinal loop in the right caudal abdo- men (Figure 1). The lesion measured 3.5 cm in length and 0.5 cm in 2 | C A S E H I S TO RY thickness. It was markedly hyperechoic with several pin-point hy- perechoic foci that produced clean acoustic shadowing suggesting a A 12-year-old neutered female mixed-breed dog was presented for a mineral component. There was no other evidence of intestinal abnor- follow-up examination 8 months after ablation of an auricular grade malities. The adjacent mesenteric fat was moderately hyperechoic This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2021 The Authors Veterinary Medicine and Science Published by John Wiley & Sons Ltd 1514 Vet wileyonlinelibrary.com/journal/vms3 Med Sci. 2021;00:1–4. wileyonlinelibrary.com/journal/vms3 | Vet Med Sci. 2021;7:1514–1517. 1 2 | ORORBIA et al. ORORBIA1515 et Al . F I G U R E 1 Sonographic image of the abdominal lesion affecting the mesentery and adjacent serosal layer of the caudal duodenum. The lesion at the mesenteric aspect of the intestinal loop is hyperechoic and ill-defined with acoustic shadowing components F I G U R E 2 Computed tomographic study. (a) Transverse and (b) dorsal images of the lesion. It is adjacent to the distal duodenum. The granular cell tumour is hyperattenuating and ill-defined with multiple pin-point mineral foci and heterogeneous. All the visualised abdominal lymph nodes were granular cell tumour. There was also mild mixed inflammation with unremarkable. The most likely organ of origin was considered the neutrophilic and macrophagic predominance and evidence of previ- mesentery with concurrent adhesion or infiltration of the adjacent ous haemorrhage. intestinal serosa. An intestinal origin was considered less likely. The A thoracic and abdominal computed tomography (CT) was per- differentials included granulomatous tissue, fat necrosis or neopla- formed for staging and surgical purposes. An irregular and heteroge- sia (primary mesenteric or atypical metastasis from the previously neous lesion with ill-defined margins was observed adjacent to the reported mast cell tumour). serosa of the caudal duodenal flexure. The lesion was mainly soft Ultrasound-guided fine needle aspiration of the lesion was per- tissue attenuation with multiple pint-point foci of mineral attenua- formed. On cytological examination a numerous and individually or- tion and mild contrast enhancement (Figure 2). The surrounding fat ganised neoplastic cells were detected. They were large, round to was heterogeneous with subtle soft tissue striations. The affected slightly polygonal with eccentric round nuclei, reticular chromatin intestinal loop was otherwise within normal limits as it was the rest and occasional prominent nucleoli. The nucleus to cytoplasm ratio of the gastrointestinal tract. The same possible origins and differen- was low. There was abundant cytoplasm with distinct cytoplasmiizc tials were considered as in the ultrasound study. No other changes borders and multiple variable shaped and sized granules. Mild aniso- or lesions suggestive of metastatic process (e.g., lymphadenopathy) cytosis and anisokaryosis were noted. Binucleated cells were fre- were found. quent and multinucleated cells were occasionally encountered. No Laparoscopic approach was performed as the owners elected a less microorganisms were seen. The findings were highly suggestive of invasive approach. A multinodular, yellowish lesion was observed around ORORBIA 1516 et Al . |3. ORORBIA et al the caudal duodenal flexure. The mass was firm and deeply attached to that they arise from the neural crest, specifically the Schwann cells. the intestinal wall and the surrounding mesenteric tissue, preventing its Evidence that the canine and human granular cell tumours shares a complete resection with the performed surgical approach. For the same similar origin has been recently published (Patnaik, 1993; Suzuki reasons, full-thickness biopsy or enterectomy were not performed. et al., 2015; Wilson, 2017). In our case, granular cells reacted mark- The main histopathological finding was a neoplastic proliferation edly to PAS and ubiquitin, as it has been previously described (Higgins of the mentioned cells with a highly infiltrative pattern in adipose et al., 2017), but no positivity was observed under Luxol fast blue and tissue. The cytoplasmic granules were periodic acid-Schiff (PAS)- S-100 protein IHC. According to this results a Schwann cell origin was positive, and immunohistochemistry revealed a strong reaction of not confirmed. S-100 negative granular cell tumours have been previ- the cells against ubiquitin (Figure 3). No positivity was observed ously reported in veterinary medicine (Reifinger et al., 2020). A defini- under Luxol fast blue and S-100 protein IHC. The diagnosis of gran- tive explanation of this fact is beyond the aim of this study. ular cell tumour was confirmed based on the pathological, immuno- Some publications in human medicine have described findings histochemical and ultrastructural findings of the neoplastic tissue. suggestive of a previous foreign body in the histopathology of granu- Six months after surgery the dog was alive and healthy without lar cell tumours (Meyer et al., 2010; Rocanti et al., 2013). In our case, evidence of clinical signs. the histological evaluation of the biopsy revealed (in addition to the granular cell population) some necrotic foci associated with reactive inflammatory cells. As no definitive foreign body was identified, those 3 | D I S CU S S I O N changes are considered secondary to the granular cell tumour. Granular cell tumour are usually benign. Malignant transformation According to our review of the literature, this is the first report de- can happen, but this is rare in both human and veterinary medicine scribing an abdominal granular cell tumour in a dog. In this case, the (Bouayyard et al., 2020; Higgins et al., 2017; Reifinger et al., 2020). tumour was in the mesentery and deeply attached to the serosal In a recent human article, a 1%–2% of malignant conversion has been layer of the caudal duodenal flexure. Unfortunately, it was not pos- described (Bouayard et al., 2020). Few reports including malignant sible to determine if the lesion originated from the mesentery or granular cell tumours have been published in veterinary patients the intestinal serosa, as enterectomy or full-thickness biopsy was (Patnaik, 1993). The present case has imaging, surgical and histo- not performed. In human medicine, up to 8%–11% of the granu- pathological characteristics suggestive of local neoplastic infiltration, lar cell tumours involve the gastrointestinal tract, most commonly but no other indications of malignancy such as lymphadenopathy or the oesophagus, colon and stomach. Small intestine involvement is evident metastatic disease were detected in the imaging studies. extremely rare (<1%), with only few cases of this tumour affecting Our patient presented for a follow-up examination after ablation of the duodenum and ileum (Barakat et al., 2018; Nakachi et al., 2000; an auricular mast cell tumour. To the authors’ knowledge, no correlation Radaelli & Minoli, 2009). Most gastrointestinal granular cell tumours has been described between granular cell tumour and mast cell tumour in human medicine arise from the mucosal or submucosal layer in neither veterinary nor human literature. In absence of any evidence (Mobarki et al., 2020; Nakachi et al., 2000). In the present case, the the authors assume that the two pathologies in this case are unrelated. lesion was in close contact with the serosal layer and mesenteric Ultrasound descriptions of granular cell tumours are lacking in vet- adipose tissue, being the other intestinal layers normal in ultrasound erinary medicine. Recently, ultrasound appearance of a celomic granu- and computed tomography. Based on these considerations, the mes- lar cell tumour has been described in a California kingsnake as a large entery is a more likely organ of origin compared to the intestine. mass, not associated with any organ, with cysts, and a wall of moderate The histogenesis of the granular cell tumour remains controver- echogenicity (Reifinger et al., 2020). In human literature, granular cell sial since its original description in 1926 (Patnaik, 1993). Initially, based tumours affecting the gastrointestinal tract have been described as hy- on light microscopic features of the neoplastic cells, the tumour was poechoic, homogenous, smooth-edged solitary lesions that appear to thought to be of skeletal muscle in origin. Neurons, fibroblasts, histio- originate from the submucosal layer (Barakat et al., 2018). Differently, cytes and myoepithelial cells are other potential origins that have been in our case, the lesion was hyperechoic, heterogeneous and it appeared proposed in human medicine (Suzuki et al., 2015). Lately it is suspected to arise from the mesentery or the intestinal serosal layer. F I G U R E 3 Round and large cell proliferation with eccentric nuclei; occasional multinucleated cells are present. Cytoplasmic granules are stained purple for periodic acid-Schiff (PAS) (a) and show marked immune reaction against ubiquitin (b). Note the infiltrative pattern in mesenteric adipose tissue 4 | ORORBIA et al. ORORBIA1517 et Al . 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