Detection of feline insulinoma with contrast-enhanced ultrasonography

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Pancreatic endocrine neoplasms are uncommon in both dogs and cats. To date, only 8 cases of feline insulinoma have been reported.¹ In affected cats, clinical signs include weakness, lethargy, and seizure-like episodes, along with persistent hypoglycemia. Once confirmed, surgical removal is the treatment of choice. However, insulinomas are typically malignant, often multifocal, and frequently already metastasized when discovered. Therefore, careful preoperative localization and screening are necessary to determine the stage of disease and whether a cat is a good candidate for surgery.

Only 1 prior case report describes the use of conventional ultrasound to diagnose insulinoma before surgery in a cat. Conventional ultrasound and CT are effective in detecting insulinomas in dogs but lack sensitivity and specificity. Nuclear scintigraphy has also been evaluated in dogs, but the cost and availability of this diagnostic modality limit its practicality. Contrast-enhanced ultrasonography (CEUS) is a less expensive imaging modality that has also been evaluated in dogs but not in cats. This case report is the first describing the use of CEUS in the diagnosis of feline insulinoma.¹

What they did

A 14-year-old neutered male domestic shorthair cat was presented with a 2-week history of clinical signs compatible with insulinoma. Among other minor abnormalities, lab work revealed severe hypoglycemia, low serum fructosamine, and increased insulin concentration. An insulin-secreting tumor was strongly suspected. The cat was placed on intravenous fluid therapy containing 2.5% dextrose, and potassium chloride and blood glucose monitoring was initiated.

Abdominal ultrasound confirmed a pancreatic mass and suggested the presence of another, smaller pancreatic nodule. Ultrasound-guided fine-needle aspirates were obtained. Cytologic examination revealed clusters of intact cells with indistinct cytoplasmic borders and uniform round nuclei containing prominent nucleoli, supporting the suspicion that the cat had an insulinoma. Some additional staging was performed, including 3-view radiographs of the chest and echocardiography. No abnormalities were detected. Medical management with prednisolone and small, frequent meals were started pending additional workup.

To better evaluate the presence of multiple lesions and/or metastatic spread before considering surgery, a CT was recommended but declined by the owner due to the cost. Therefore, CEUS, a less costly alternate imaging modality, was used. The cat was placed under general anesthesia and 2 CEUS studies were performed. Each study used 1.0 ml of a reconstituted microbubble contrast agent. The first study evaluated the liver from 10 seconds before until 3 minutes after contrast administration. Homogeneous contrast uptake by the hepatic parenchyma was observed. The second study was performed 30 minutes later and evaluated the pancreatic parenchyma in the same way. Uniform enhancement of the pancreas was observed, with a rapid increase in its echogenicity, peaking at 30 seconds post-injection and followed by a rapid washout. The previously identified mass presented a lower contrast uptake than the surrounding parenchyma at peak contrast enhancement. In addition, 2 ill-defined smaller nodules were also identified caudal to the larger mass. One of these additional nodules was suspected on conventional ultrasound, while the other wasn’t visible. Multifocal pancreatic disease was considered likely based on the CEUS findings.

The cat was taken to surgery. The larger mass was macroscopically visible, while the smaller ones required gentle palpation of the pancreas to identify. A hemi-pancreatectomy of the left lobe of the pancreas was performed to remove the 3 nodules.

What they found

Following surgery, histopathology of the masses revealed a multifocal islet cell carcinoma. Immunohistochemistry was performed and neoplastic cells showed marked positive staining for insulin and negative staining for chromogranin A, glucagon, and somatostatin.

Clinically, the cat’s blood glucose concentration remained elevated for several days following surgery but was normal by discharge. Prednisolone treatment was progressively tapered over a 10-day postoperative period. After that time, further monitoring was declined by the owner, and the cat was reported to be clinically normal.

Six months later, the cat was presented again for vomiting and difficulty defecating. Bloodwork and urinalysis were normal. Abdominal radiographs and ultrasound were performed, revealing severe obstipation and a poorly visualized colon. The owner declined additional diagnostics and elected exploratory laparotomy. A large mass was found at the colorectal junction and resected. Histopathology was consistent with an adenocarcinoma with infiltrated margins. No immunohistochemistry was performed. Because the cat remained normoglycemic, the tumor was thought to be a primary adenocarcinoma and not a metastasis from the prior insulinoma. One month later, the cat was euthanized due to recurring clinical signs of obstipation.

Take-home message

When evaluating pancreatic neoplasms in the cat, CEUS may be a helpful presurgical screening tool and allow detection of lesions not apparent on conventional abdominal ultrasound. Because this is the only case report, further studies are warranted to evaluate this technique.

Miranda Spindel, DVM, MS, serves as the shelter medicine consultant and student advocate for VIN. She initiated and completed the first residency in shelter medicine with a master’s of clinical sciences through Colorado State University in 2007, and then worked as the senior director of shelter medicine at the ASPCA for 10 years. She is a member of the Shelter Medicine Organizing Committee and Residency Committee for Shelter Medicine for the American Board of Veterinary Practitioners. Spindel lives on a small acreage in Colorado with her daughter and dogs, cats, chickens, horses, and donkeys.

Reference

1. Cervone M, Harel M, Ségard-Weisse E, Krafft E. Use of contrast-enhanced ultrasonography for the detection of a feline insulinoma. J Feline Med Surg Open Rep. 2019;5(2):2055116919876140. doi:10.1177/2055116919876140