Page 534 - Small Animal Internal Medicine, 6th Edition

506 PART III Digestive System Disorders

PERIANAL NEOPLASMS benign masses. Finding metastases (e.g., regional lymph
nodes, lungs) is the most definitive method of determining
VetBooks.ir ADENOCARCINOMA malignancy.
ANAL SAC (APOCRINE GLAND)
Treatment
Etiology Surgical excision is preferred for benign or solitary tumors
Anal sac adenocarcinomas are derived from the apocrine that have not metastasized. Neutering is recommended
glands and are usually found in older female dogs. for dogs with adenomas. Radiation is recommended for
multicentric and some malignant tumors. Chemother-
Clinical Features apy is helpful in some dogs with adenocarcinomas (see
An anal sac or pararectal mass can often be palpated, but Chapter 76).
some are not obvious. Paraneoplastic hypercalcemia causing
hyporexia, weight loss, vomiting, and polyuria-polydipsia Prognosis
is common. Occasionally, constipation due to hypercal- The prognosis is good for benign lesions but guarded for
cemia or perineal mass occurs. Metastasis to sublumbar malignant lesions.
lymph nodes occurs early, but metastases to other organs
are rare.
CONSTIPATION
Diagnosis
Cytologic and/or histopathologic evaluation is necessary to Constipation may be caused by any perineal or perianal
establish a diagnosis. Hypercalcemia in an older female dog disease already discussed that causes pain (e.g., perianal fis-
should lead to careful examination of both anal sacs and tulae, perineal hernia, anal sacculitis) or obstruction as well
pararectal structures. Abdominal ultrasonography may as anything causing colonic weakness. It may also be caused
reveal sublumbar lymphadenopathy. by other disorders (see Box 26.15).
Treatment
Hypercalcemia, if present, must be treated (see Chapter 53). PELVIC CANAL OBSTRUCTION CAUSED
The tumor should be removed, but these tumors have often BY MALALIGNED HEALING OF OLD
metastasized to regional lymph nodes by the time of diagno- PELVIC FRACTURES
sis. Palliative chemotherapy (see Chapter 76) may be tran-
siently beneficial in some dogs. Etiology
Prior trauma (e.g., automobile-associated injuries) is a
Prognosis common cause of pelvic canal obstruction in cats because
The prognosis is guarded. they frequently sustain pelvic trauma that heals if they are
allowed to rest. Cats appear clinically normal once the frac-
tures heal, but diminution of the pelvic canal can produce
PERIANAL GLAND TUMORS megacolon and/or dystocia.

Etiology Diagnosis
Perianal gland tumors arise from modified sebaceous glands. Digital rectal examination should be diagnostic. Radio-
Perianal gland adenomas have testosterone receptors. graphs will further define the extent of the problem.

Clinical Features Treatment
Perianal gland adenomas are often sharply demarcated, Constipation caused by minimal pelvic narrowing may be
raised, and red, and they may be pruritic. Commonly found controlled with stool softeners, but orthopedic surgery may
around the anus and base of the tail, they may be solitary or be necessary. The prognosis depends in part on how severely
multiple and can occur over the back half of the dog. Male the colon has been distended. Unless the colon is massively
hormones appear to stimulate their growth, and they are stretched out of shape, it can often resume function if it is
often found in older intact male dogs (especially Cocker kept empty and allowed to regain its normal diameter. Pro-
Spaniels, Beagles, and German Shepherds). Pruritus may kinetic drugs such as cisapride (0.25 mg/kg PO q8-12h) may
lead to licking and ulceration of the tumor. Perianal gland stimulate peristalsis but must not be used if there is residual
adenocarcinomas are rare; they are usually large, infiltrative, obstruction.
ulcerated masses with a high metastatic potential.
Prognosis
Diagnosis The prognosis depends on the severity and chronicity of
Cytologic and/or histopathologic evaluation is required for colonic distention and surgical success in widening the
diagnosis, but neither reliably distinguishes malignant from pelvic canal.