A light and electron microscopic study of a normal adrenal medulla and a pheochromocytoma from a horse

Clinical and Pathological Features of Pheochromocytoma in the Horse: A Multi-Center Retrospective Study of 37 Cases (2007-2014)

Background

Pheochromocytoma is the most common adrenal medullary neoplasm of domestic animals, but it is rare in horses. Antemortem diagnosis in horses is difficult, with clinical signs often being vague or non‐specific.

Objective

The objective of this study was to describe the clinical, laboratory, and pathologic findings of pheochromocytoma in horses.

Animals

Thirty‐seven horses diagnosed with pheochromocytoma based on postmortem examination from 2007 to 2014.

Methods

Retrospective case series.

Results

Pheochromocytoma was identified in 37/4094 horses during postmortem examination. Clinical signs consistent with pheochromocytoma had been observed antemortem in only 7 cases, with the remainder being incidental findings. Colic was the most common presenting complaint (13 of 37 cases) and tachycardia was noted in 95% of cases (median heart rate of 86 bpm in clinical cases). Hyperlactatemia (median, 4.9 mmol/L) and hyperglycemia (median, 184 mg/dL) were the most common clinicopathologic abnormalities. Hemoperitoneum caused by rupture of pheochromocytoma was noted in 4/7 clinical cases. Concurrent endocrine abnormalities (eg, thyroid adenoma, adrenal hyperplasia, pituitary pars intermedia hyperplasia or adenoma, parathyroid C‐cell carcinoma) were found in 27/37 horses, with 8/37 horses having lesions consistent with multiple endocrine neoplasia syndrome as described in humans.

Conclusions

Pheochromocytoma was diagnosed in 0.95% of horses presented for necropsy. The majority of these were incidental findings, but pheochromocytoma was thought to contribute to clinical findings in 19% of cases, and multiple endocrine neoplasms were commonly seen. Usually an incidental finding at necropsy, pheochromocytoma may cause acute death from intraperitoneal exsanguination and should be considered in horses presenting with colic, tachycardia, and hemoperitoneum.

Phaeochromocytoma in two coatimundi (Nasua nasua)

Two unrelated coatimundi (Nasua nasua) had bilaterally enlarged adrenal glands at necropsy, and sections of the glands from both animals had histopathological features consistent with neoplasia. They were differentiated from an adrenal cortical tumour on the basis of their light microscopical morphology, immunoperoxidase staining and electron microscopic studies and a final diagnosis of phaeochromocytoma was made. To the authors' knowledge, these are the first reported cases of phaeochromocytoma in coatimundi.

Abdominal neoplasia (excluding urogenital tract)

Neoplasia of the equine gastrointestinal tract and abdominal organs occurs predominantly in geriatric horses, although lymphoma and hepatocellular carcinoma and a few other neoplasms can be found in young horses. This article discusses diagnostics that can be used in weight-loss situations, suspicious of neoplasia, as well as tumors themselves including clinical signs, diagnostic tools, histopathologic appearance, and management.

Ultrastructural and biochemical evaluation of adrenal medullary hyperplasia and pheochromocytoma in aged bulls

Pheochromocytomas and adrenal medullary hyperplasia were investigated ultrastructurally and by assaying catecholamines in tissue and urine. Three of seven bulls had concomitant thyroid C-cell neoplasms and normal parathyroid glands. Pheochromocytomas were either bilateral or unilateral, and were composed of large chromaffin cells predominantly in the storage phase of the secretory cycle. Two pheochromocytomas were composed of cells with ultrastructural characteristics of the epinephrine-secreting type and contained round secretory granules of low electron density. The norepinephrine-secreting type of chromaffin cell predominated in one pheochromocytoma and had storage granules with an electron-dense, eccentric core and a wide submembranous space. Two pheochromocytomas were composed of a mixture of epinephrine- and norepinephrine-secreting cells. Adrenal medullary hyperplasia in four bulls consisted of multinodular or diffuse areas of hyperchromatic chromaffin cells that were non-encapsulated, and compressed adjacent cortical tissue. Tissue and urinary concentrations of norepinephrine were increased in bulls with adrenal medullary hyperplasia or pheochromocytoma, but urinary vanillylmandelic acid and unconjugated epinephrine levels were not different from those of control bulls with a normal adrenal medulla.