Ganglioneuromatosis in a Horse
NECROPSY REQUEST
CLINICAL DIAGNOSIS:
Upward fixation of patella / OCD.
HISTORY: Donated for multiple musculoskeletal abnormalities. Has
upward fixation of patella and stifle effusion. Suggested of OCD.
CLINICAL QUESTIONS: None.
NECROPSY GROSS REPORT
ANIMAL
IDENTIFICATION:
A 476kg, eight-year-old, bay, mixed breed gelding with white socks up to the
fetlock on all but the right hind leg and a star is presented for necropsy in
fair body condition.
INTEGUMENTARY AND SPECIAL SENSES: Shaved areas include: an 8 x 12cm
area caudal to the scapula on the thorax, and a 7 x 6cm area on the tail
head. The area on the thorax has several biopsy sites. The coronary band has
moderate crusting.
RESPIRATORY: The lungs are aerated and do not collapse (chronic
obstructive pulmonary disease, presumed).
CARDIOVASCULAR (Heart weight: 3.78kg. The right ventricular free wall
is 1.5cm in width. The left ventricular free wall is 4cm in width.): The
medial leaf of the right atrioventricular valve has a 0.5 x 1cm, dark red,
fluid-filled cyst (valvular hematocyst). The right aortic valve has a 1cm
diameter, white, fibrotic nodule (friction rub) that faces a similar, 4mm
nodule on the medial aortic valve leaflet.
LIVER AND PANCREAS (Liver weight: 6.64kg): Numerous, tan/white
strands are tightly adhered to the diaphragmatic surface of the capsule of the
liver, especially of the right lobe (perihepatitis filamentosa).
DIGESTIVE: Numerous, sessile to pedunculated, white to purple nodules
are on the antimesenteric wall of the small colon, 40cm from the anus. On cut
surface, the purple nodules are firm, solid, and red. The nodules range from
3mm to 1.5cm, with the smaller nodules tending to be white, and the larger
nodules purple. The mucosa opposite these masses have scattered, 2-4mm
pittings. The nodules have adhesions to the mesentery (focal colitis with
lymphadenitis).
MUSCULOSKELETAL: The right stifle joint has yellow, edematous
proliferation on the synovium (villous proliferation and aseptic synovitis,
presumed). The left stifle also has nodular proliferation of the synovium
(aseptic synovitis, presumed).
HEMIC AND LYMPHATIC (Spleen weight: 5.44kg), URINARY (Right
kidney weight: 0.792kg; left kidney weight: 0.802kg), GENITAL,
ENDOCRINE, NERVOUS (Brain weight: 0.636kg): No significant lesions
observed.
POSTMORTEM ANALYSIS AND DIAGNOSIS:
The cause of death is euthanasia due to patellar upward fixation. The
proliferation in both of the stifle joint linings suggests synovitis. The
uncollapsed lungs are suggestive of COPD. The focal colitis is presumed
related to overzealous palpation. Numerous, practice procedures have been
performed on this animal prior to necropsy. Limited histology is pending.
TENTATIVE DIAGNOSIS:
COPD, Synovitis.
(Fig. 1 Multiple nodules, ranging in size from 3 mm to 1.5 cm, are extending from the serosal surface of the small colon.)
(Fig. 2 A cross section of one of the nodules following formalin fixation. The nodule is arising in the area of the myenteric plexus and replaces the tunica muscularis.)
NECROPSY HISTOPATHOLOGY REPORT
MICROSCOPIC LESIONS:
Stifle joint: Mild synovial proliferation.
Pastern skin: Superficial perivascular dermatitis with small vessel
vasculitis and severe serous crusting.
Small colon: Ganglioneuromatosis.
DIAGNOSIS: Euthanasia; Ganglioneuromatosis; Pastern leukocytoclastic
vasculitis, presumed.
(Fig. 3 Microscopically, the nodules are composed of fascicles of nerve processes and well-differentiated neuronal cell bodies.)
(Fig. 4 Higher magnification, showing neuronal cell bodies (thin arrow) and fascicles of nerve processes with Schwann cells (thick arrow).)
INTERPRETIVE SUMMARY/COMMENTS: Leukocytoclastic dermatitis is seen in mature horses in distal limbs with white socks. It is thought to be a photodynamic lesion. Ganglioneuromas are benign tumors arising from enteric ganglia. They contain well-differentiated neurons, nerve processes, and supporting cells. The term ganglioneuromatosis is used when a segmental area of the GI tract is affected.
