Anal Sac Adenocarcinoma with Vertebromedullary Metastasis in a Cocker Spaniel

Background: Several neoplasms can affect the perianal region, being the hepatic adenoma and the anal sac adenocarcinoma (ASAC), which is considered the most frequent. The ASAC is a malignant neoplasm originating from the secretory epithelium of the perianal apocrine glands and is rarely seen in veterinary medicine. The ASAC occurs mainly in adult to elderly canines with high metastasis rates. Patients may be asymptomatic or manifest discomfort and behavioral changes. In the presence of metastasis, the most frequent clinical signs are inappetence, coughing, dyspnea, and colorectal obstruction. Given this scenario, this paper aims to describe the clinical presentation, diagnostic examination, and necropsy findings of a Cocker Spaniel with ASAC and metastasis in the vertebral body, spinal cord, and cauda equina. Case: A 8-year-old neutered male Cocker Spaniel (12 kg of body mass) with a clinical history of non-ambulatory paraparesis was evaluated. The patient also presented tenesmus, difficulty to defecate, and the presence of nodules in the anal sac area. On the neurological examination, asymmetrical changes compatible with injury between L4-S3 were found. A complete blood count, serum biochemistry, and imaging exams such as plain radiography, abdominal ultrasonography (US), and magnetic resonance imaging (MRI) were requested. Blood count revealed anemia and neutrophilic leukocytosis and hypercalcemia. The liver showed increased echogenicity and thickened pancreas in the abdominal US scan. A slightly heterogeneous, vascularized mass with irregular borders was identified in the topographic region of the sublumbar lymph nodes; MRI images demonstrated an expansile formation in the ventral region of the lumbosacral spine, corresponding to the sublumbar lymph nodes and interruption of the cerebrospinal fluid at L5, suggestive of compression of the spinal cord and cauda equina. A presumptive diagnosis of perianal neoplasm with metastasis was made based on the complementary exams. The dog was referred to necropsy, which revealed a 4 cm tumor in the perianal region that invaded the pelvic canal. Multifocal nodules were present on the lung surface, liver, and kidneys, suggesting metastasis. On the cross-section of the spine, one could note the presence of the tumor in the vertebral bodies, spinal cord, and cauda equina from L5 to S3. Even with histopathological evaluation of the tumor, only the immunohistochemical analysis allowed us to confirm the anal sac adenocarcinoma. Discussion: Adenomas and carcinomas are perianal gland neoplasms common in adult and elderly male dogs; the Cocker Spaniel breed is among the most affected. The clinical signs presented by the patient, such as tenesmus and difficulty in adopting the posture of defecation, are common, although neurological changes are rare. As for metastasis, carcinomas of the perianal region present high chances of metastasis to organs including the liver, kidneys, and lungs, both lymphatically and hematogenously, but few studies have related these factors to neurological alterations due to metastasis. We concluded that metastases from carcinomas to the spine must be considered a possible differential diagnosis in cases of patients presenting clinical signs that are compatible with spinal cord compression and a history of previous neoplasm.