Insulinoma in a senior pit bull: Anatomic pathology perspective

Dr. Lani BowerIslet cell tumors arise from one of the five microscopically indistinguishable cell types composing the pancreatic islet. Insulinomas, arising from the beta cell, are the most common hormonally functional islet cell tumor presented for histologic evaluation. As discussed previously, most of these tumors are behaviorally aggressive, commonly metastasizing by the time of diagnosis.

Grossly, many islet cell tumors are light tan to yellow, making them difficult to distinguish from the surrounding normal pancreatic parenchyma (Figure 5).1

Figure 5. An islet cell tumor from another patient (arrow).Most range from microscopic to 3 cm, while few may be significantly larger and irregularly lobulated with hemorrhage (Figure 6).

Figure 6. An islet cell tumor from another patient (arrow).Gross appearance does not always correlate with extent of local invasion and metastasis (Figure 7).

Figure 7. An islet cell tumor from another patient (long arrow) with mesenteric and lymph node metastasis short arrows).Common sites of metastasis include the regional lymph nodes, liver, mesentery and omentum.1 Occasionally, there can be multiple primary pancreatic tumors.

Histopathologic examination is needed to diagnose an islet cell tumor and evaluate for invasiveness. These tumors are often sharply demarcated from the adjacent parenchyma and are surrounded by a partial to complete thin fibrous capsule (Figure 8).

Figure 8. An islet cell tumor from the dog in this case. Neoplastic cells are surrounded by a thin fibrous capsule. Normal pancreas is in upper left.Lobules are separated by fibrous trabeculae and are composed of polygonal cells in packets, nests, rows and, less often, form rosettes (Figure 9) and acini. Islet cell tumors are often minimally pleomorphic with low numbers of mitotic figures2; thus, malignancy is determined most often by evaluating for invasion through the fibrous capsule into the surrounding parenchyma, mesentery or vascular invasion.3

Figure 9. An islet cell tumor from the dog in this case. Polygonal cells are arranged in rows and packets. Rosettes are composed of neoplastic cells palisading around a clear space (asterisk).Islet cell tumors may be difficult to differentiate from pancreatic exocrine carcinomas grossly and sometimes histologically. Immunohistochemistry is necessary for a definitive diagnosis and may be particularly useful in cases without a clinical history consistent with hyperinsulinemia. Most insulinomas stain positive for insulin, neuron-specific enolase (NSE) and chromogranin A.4

References

1. Meuten DJ. Tumors of the endocrine glands. In: Tumors in domestic animals. 4th ed. Ames: Iowa State Press, 2002.

2. Roccabianca P, Rondena M, Paltrinieri S, et al. Multiple endocrine neoplasia type-I like syndrome in two cats. Vet Pathol 2006;43:345-352.

3. Isidoro-Ayza M, Lloret A, Bardagí M, et al. Superficial necrolytic dermatitis in a dog with an insulin-producing pancreatic islet cell carcinoma. Vet Pathol 2014;51:805-808.

4. Hawkins KL, Summers BA, Kuhajda FP, et al. Immunocytochemistry of normal pancreatic islets and spontaneous islet cell tumors in dogs. Vet Pathol 1987;24:170-179.

Let's go back to the hall to check out another perspective.