Oligodendroglioma

From Dog
Typical MRI findings with a high grade oligodendroglioma, showing ring enhancing, mass effect and ventricular involvement[1]

Oligodendrogliomas, a form of glioma, are common brain tumours in dogs, particularly in brachycephalic breeds.

These tumors are a type of glioma that are believed to originate from the oligodendrocytes of the brain or from a glial precursor cell. Glial tumors (specifically astrocytomas and oligodendrogliomas) are the second most common group of canine brain tumors. Most grow by infiltration and destroy invaded tissue.

Breeds such as the Boxer, Bulldog and Boston Terrier are predisposed.

These tumors occur most frequently in the cerebral hemispheres (mostly the frontal and temporal lobes) and thalamus[2] and associated with both gray and white matter.

High grade oligodendrogliomas commonly invade into the ventricular system, but migration across the corpus callosum is rarely seen. In some patients more extensive metastases may be noted, with involvement of the brainstem, spinal cord, leptomeninges[3] and eye[4].

Primary and secondary tumours can occur simultaneously, with one dog reportedly suffering both an oligodendroglioma and metastatic mammary adenocarcinoma[5].

Clinically affected dogs usually present with neurological symptoms of reasonably rapid onset, with ataxia, proprioceptive deficits, cranial nerve deficits, seizures and changes in mentation.

Diagnosis requires specialist imaging with CT or MRI. With MRI imaging, these tumors are usually intraaxial masses that are hypointense on T1Wi mages and hyperintense on T2W images. Contrast enhancement is often peripherally ring enhancing, and more common with grade III than grade II tumors[6]. Intratumoral calcification is uncommon.

These tumors often exhibit marked mass effect and are often relatively well demarcated and can involve ventricular structures.

Definitive diagnosis is made with histopathological analysis of biopsied material. Microscopically, these tumors appear as polygonal to round cells characterized by moderate pale, basophilic, and vacuolar cytoplasm with round to slightly oval, centrally located nuclei with fine-stippled heterochromatin, a single nucleolus, and a very low mitotic activity. Oligodenrogliomas usually lack glial fibrillary acidic protein, vimentin, factor VIII-related, and cytokeratin antigen expression[7].

A differential diagnosis would include astrocytoma, choroid plexus tumor, primary central nervous system lymphoma, primitive neuroectodermal tumor, histiocytoma and vascular hamartoma[8].

Treatment options vary from conservative treatment with short-term prednisolone to obviate peritumoral edema associated with the mass[9], to radiation therapy, chemotherapy to surgical debulking[10].

Because most patients either develop or present with seizures, anticonvulsive therapy is recommended once the patient is diagnosed with oligodendroglioma.

References

  1. UC Davis
  2. Young BD et al (2011) Magnetic resonance imaging features of intracranial astrocytomas and oligodendrogliomas in dogs. Vet Radiol Ultrasound 52(2):132-141
  3. Koch MW et al (2011) Multifocal oligodendroglioma in three dogs. J Am Anim Hosp Assoc 47(5):e77-85
  4. Naranjo C et al (2008) Canine ocular gliomas: a retrospective study. Vet Ophthalmol 11(6):356-362
  5. Alves A et al (2006) Primary and secondary tumours occurring simultaneously in the brain of a dog. J Small Anim Pract 47(10):607-610
  6. Sutherland-Smith J et al (2011) Magnetic resonance imaging apparent diffusion coefficients for histologically confirmed intracranial lesions in dogs. Vet Radiol Ultrasound 52(2):142-148
  7. Mamom T et al (2004) Oligodendroglioma in the cervical spinal cord of a dog. Vet Pathol 41(5):524-526
  8. Snyder JM et al (2006) Canine intracranial primary neoplasia: 173 cases (1986-2003). J Vet Intern Med 20(3):669-675
  9. Dickinson PJ et al (2008) Vascular endothelial growth factor mRNA expression and peritumoral edema in canine primary central nervous system tumors. Vet Pathol 45(2):131-139
  10. Hasegawa D et al (2011) Long-Term Survival in a Dog with Anaplastic Oligodendroglioma Treated with Radiation Therapy and CCNU. J Vet Med Sci 74(11):1517-1521