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Clinical Rounds: Meningioma in a 9-year-old chocolate Lab
The brain-a dense and intricate collection of neurons and glial cells that controls all things. When tumors invade-even the covering of the brain, the meninges-it seems an especially sinister form of cancer. The team at the University of Tennessee helped extend this dog's life by using the latest information on meningioma management.
The Clinical Rounds team is from the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee.
Clinical rounds coordinator: Jeanne Larson, DVM, DACVIM (oncology)
Radiology: Silke Hecht, Dr.med.vet, DACVR, DECVDI
Neurology: Courtney Sampson, DVM
Anatomic pathology: Jennie Jankovsky, DVM
Radiation oncology: Isabella Pfeiffer, DMV, DECVIM-CA (oncology), DACVR (radiation oncology)
Medical oncology: Lark Walters, DVM
Dr. Jeanne LarsonMeningiomas are the most common primary brain tumor seen in dogs.1 These extra-axial tumors arise from the arachnoid layer of the meninges. Meningiomas generally occur in older dogs, and dolichocephalic breeds are overrepresented.2 While the metastatic potential of canine meningiomas is low, they are locally invasive and damage local brain tissue as they grow and cause peritumoral edema, inflammation and hemorrhage. Neurologic signs vary depending on the location of the meningioma within the brain, and seizure activity is the most common clinical sign in dogs.2 Other common clinical signs include ataxia, blindness and behavior changes.
A 9-year-old castrated male chocolate Labrador retriever was referred to the University of Tennessee (UT) Veterinary Medical Center Oncology department to discuss treatment options for a recently diagnosed primary brain tumor. One month before presentation, the dog had an acute onset of generalized seizure activity. At that time, he was evaluated by a local veterinary neurologist who prescribed levetiracetam and prednisone. Full laboratory work including a complete blood count, a serum chemistry profile and electrolyte panel, and thyroxine (T4) concentration was performed. The patient's T4 concentration was elevated (5.5 µg/dl; reference range = 0.8 to 3.5 µg/dl), and the remainder of the blood work showed no abnormalities.
Palpation of the patient's neck revealed a 5.5-x-3.7-x-2.2-cm, freely moveable mass in the area of the right thyroid gland. A brain magnetic resonance imaging (MRI) scan was performed, which demonstrated a 1.5-x-1.5-cm extra-axial mass in the left olfactory lobe. Differential diagnoses included meningioma, nasal adenocarcinoma, fungal granuloma and lymphoma. Under the same anesthetic episode as for the brain MRI scan, the ventral neck mass was surgically excised. Histopathologic examination revealed a narrowly excised thyroid carcinoma.
Tumor staging and treatment
Upon presentation to UT, the patient was neurologically normal and had no reported seizure activity with the combination of levetiracetam and prednisone. A consultation with the neurology department and evaluation of the brain MRI scan determined that the brain mass was surgically accessible. Three-view thoracic radiographs and abdominal radiographs and ultrasonograms showed no significant abnormalities.
A craniotomy was performed by the UT neurology department, and the brain tumor was debulked. Histopathologic examination confirmed a meningioma. The patient did well postoperatively and was continued on levetiracetam and a tapering dose of prednisone. Definitive radiation therapy was recommended because of the incomplete tumor excision.
Several weeks later, the patient presented for a postoperative planning computed tomography (CT) scan before definitive radiation therapy. The scan revealed that most of the meningioma had been removed, but there was a persistent 2.3-x-1.5-x-0.3-cm ring-enhancing area associated with the left olfactory and frontal lobes, which was thought to represent residual tumor tissue or postsurgical inflammatory change. In addition, a 4.5-x-2.7-x-1.7-cm mass associated with the right retropharyngeal lymph node was noted on the CT scan; cytology confirmed carcinoma, raising strong suspicion of local thyroid carcinoma metastasis.
Definitive radiation therapy was pursued (16 treatments of 3 Gy) for the meningioma; in addition, palliative radiation therapy (five treatments of 4 Gy) was administered to the right retropharyngeal lymph node. The patient did well during treatment. Artificial tears were prescribed because of the development of transient keratoconjunctivitis sicca; levetiracetam was continued and prednisone was reinstituted to alleviate inflammation associated with acute radiation side effects. Further treatment for the thyroid carcinoma was discussed, including the potential for chemotherapy. The client opted for close monitoring.
After the completion of radiation therapy, the patient had several follow-up appointments with his local neurologist and was reported to be doing very well clinically. He was tapered off prednisone over a period of one month; levetiracetam was continued long-term. Repeat three-view thoracic radiographs were taken three months later and showed no evidence of pulmonary metastasis.
Eight months later, he presented to the UT oncology department for evaluation. He was neurologically normal and had no reported seizure activity. A recheck CT scan was performed to evaluate the brain, neck and thorax. No evidence of meningioma recurrence was seen and there was no evidence of pulmonary metastasis. However, the right medial retropharyngeal lymph node was further enlarged-now measuring 5.1-x-3.9-x-2.4 cm-indicating persistent metastatic disease from the thyroid carcinoma. Abdominal radiographs and ultrasonograms revealed no abnormalities.
Treatment options for the metastatic right medial retropharyngeal lymph node were discussed, including continued monitoring, chemotherapy or surgical removal. The client elected to proceed with surgical removal, which was scheduled for several days later. The night before surgery, the patient's regular dose of levetiracetam was inadvertently delayed, and a grand mal seizure occurred. The patient was presented to the UT emergency department for monitoring, levetiracetam was administered, and no further seizure activity was seen. Surgical removal of the metastatic lymph node was performed the following day without complication. Histopathologic examination confirmed thyroid carcinoma metastasis.
After discharge from the hospital, continued seizure activity was observed. The patient was hospitalized with his local neurologist. Dexamethasone, zonisamide, phenobarbital and continued levetiracetam were administered. Differential diagnoses for acute onset of seizure recurrence included tumor recurrence, late side effects from radiation, postoperative scar tissue or idiopathic epilepsy. A brain MRI scan was performed, which was most consistent with inflammation around the surgical and radiation site. Antibiotics were also prescribed because of concern for potential infection. The patient improved for a short period, but later deteriorated with continued seizure activity and passed away. Overall survival time was one year after the initial onset of seizure activity.
1. Snyder JM, Shofer FS, Van Winkle TJ, et al. Canine intracranial primary neoplasia: 173 cases (1986-2003). J Vet Intern Med 2006;20:669-675.
2. Bagley RS, Gavin PR, Moore MP, et al. Clinical signs associated with brain tumors in dogs: 97 cases (1992-1997). J Am Vet Med Assoc 1999;215:818-819.
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