JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
October2021
D-P24 (NP)
Signalment (JPC #1817473): Young horse
HISTORY: At necropsy, there were numerous elevated subserosal masses in the terminal small intestine that ranged in color from bright red to yellow and brown.
HISTOPATHOLOGIC DESCRIPTION: Small intestine: Multifocally, the serosa is expanded up to 1 mm by numerous small-caliber blood vessels, minimal hemorrhage, increased fibrous connective tissue, moderate numbers of macrophages, lymphocytes, plasma cells, fewer eosinophils, ectatic lymphatics, and increased clear space (edema). Macrophages often contain cellular debris and there is multifocal moderate erythrophagocytosis and hemosiderosis. Multifocally, the submucosa is expanded up to 3 mm thick by edema. Diffusely the submucosa and lamina propria are infiltrated by low to moderate numbers of previously described inflammatory cells, including erythrocyte-laden macrophages. Few intestinal crypts contain necrotic debris and neutrophils (crypt abscesses) and there is mild blunting of intestinal villi.
MORPHOLOGIC DIAGNOSIS: 1. Small intestine, serosa: Serositis, lymphoplasmacytic and histiocytic, subacute, multifocal, moderate, with fibrosis, erythrophagocytosis, hemosiderosis and edema, horse, breed unspecified, equine.
- Small intestine: Enteritis, lymphoplasmacytic, chronic, diffuse, mild, with crypt abscesses and submucosal erythrophagocytosis.
CONDITION: Hemomelasma ilei
GENERAL DISCUSSION:
- Common incidental finding in horses
- Slightly elevated subserosal hemorrhagic plaques usually found along the antimesenteric border of the ileum or rarely on the large bowel, but can occur anywhere along the intestine
- Lesions are generally of no clinical consequence but can lead to intestinal strictures and intermittent colic
PATHOGENESIS:
- Unknown cause; may be associated with trauma by migrating larvae of edentatus or other Strongylus sp.; however, parasites have not been reported in the lesions, and the incidence has not apparently declined with the reduction in large stronglye infections over the last 25 years
- Current hypotheses include susceptibility of weak serosal blood vessels to tearing secondary to hyperperistalsis of a muscular ileum or serosal vascular injuries from intestinal kinking
TYPICAL CLINICAL FINDINGS:
- Usually asymptomatic; has been associated with mild clinical cases of intestinal strictures or mild colic (non-fatal), primarily in young horses
TYPICAL GROSS FINDINGS:
- Slightly elevated, antimesenteric, subserosal pink to black plaques, 1-4 cm in diameter; occur anywhere in the intestine but most commonly ileum
- Hemorrhages, ulcers, and a catarrhal exudate may be present on the intestinal mucosal surface
- With time, lesions resolve to yellow, brown, or tan fibrotic plaques
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Serosal thickening with histiocytic plaques and variably mature fibrous tissue
- Edema, hemorrhage, mixed inflammatory infiltrate; macrophages containing erythrocytes, hemosiderin, and cellular debris
- Variably mature fibrous tissue
DIFFERENTIAL DIAGNOSIS:
- For serosal plaques:
- Equine granulomatous enteritis: Fibrovascular serosal plaques with similar distribution and character
COMPARATIVE PATHOLOGY:
- Comparable lesions not reported in other veterinary species
REFERENCES:
- Gelberg, HB. Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:373.
- Buergelt CD, Del Piero F. Equine Pathology. Ames, IA: John Wiley & Sons, Inc.; 2014:159-160.
- Niazmand MH, Hirai T, Ito S, et. al. Causes of death and detection of antibodies against Japanese encephalitis vitus in Misaki feral horses (Equus Caballus) in Southern Japan. 2015-17. J Wildl Dis. 2019;55(4):804-811.
- Uzal FA, Plattner BL, Hostetter JM. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier; 2016:216-217.
