Regardless of whether the brain tumor is primary or metastatic, clinical signs are usually slowly progressive over several
weeks to months or may be rapid in onset and have a short clinical course. Most dogs with brain tumors will have long histories
of vague signs that may be overlooked until signs of brain dysfunction are well advanced.
The clinical signs of brain neoplasms include anorexia, seizures, altered behavior, circling, head pressing, compulsive walking,
altered consciousness and locomotor disturbances.
Cerebral tumors will typically cause behavior changes, seizures, visual deficits and circling. Brain stem tumors will typically
cause depression, head tilt, cranial nerve deficits, weakness and ataxia. Cerebellar tumors will typically cause ataxia, head
tilt, circling and tremor.
Choroid plexus tumors may also include signs of vomiting and bradycardia. Acute onset of blindness and dilated non-responsive
pupils may be the only clinical signs of an intracranial tumor and are usually located in the chiasmal region.
Survey skull radiographs, cerebrospinal fluid analysis and/or special imaging techniques such as computerized tomography or
magnetic resonance imaging are commonly incorporated in the clinical evaluation of a suspect dog for neoplasia of the central
Survey skull radiographs are of limited value in the diagnosis of a primary brain tumor; however, they may be helpful in the
detection of neoplasms of the skull or nasal cavity that have affected the brain by local extension. Radiographs of the skull
may occasionally reveal erosion or hyperostosis of the calvarium in association with a primary brain tumor (e.g., meningioma)
or document areas of mineralization within a neoplasm.
Cerebrospinal fluid analysis is often helpful in evaluating dogs suspected of having an intracranial tumor, especially if
the tumor communicates with the ventricles or subarachnoid space.
Although, cerebrospinal fluid changes are often nonspecific, when combined with the history and neurologic examination, such
changes may provide an accurate diagnosis. Cerebrospinal fluid analysis may reveal a definitive diagnosis if neoplastic cells
are visualized, but this is unusual unless its lymphosarcoma. Unless neoplastic cells are present, the cerebrospinal fluid
analysis will provide only indirect evidence that a tumor exists. In general, increased cerebrospinal fluid protein content
and normal to increased cerebrospinal fluid white blood cell counts are considered the typical changes seen with brain tumors.
Meningiomas are more commonly associated with a neutrophilic pleocytosis; however, pleocytosis can be seen with other tumors
as well. Choroid plexus papillomas may cause dramatic increases in cerebrospinal fluid protein concentration. Primary intracranial
neoplasia is usually associated with a cerebrospinal fluid white blood cell count of fewer than 50 cells/µL with variable
elevations of cerebrospinal fluid protein. In contrast, metastatic or invasive neoplasia is associated with higher white blood
cell counts and protein concentrations in the cerebrospinal fluid.
Because most intracranial tumors are not visible with survey radiographs, computerized tomography and magnetic resonance imaging
allow for localization of tumors, facilitate brain biopsy, determine the feasibility of surgical removal of a tumor, allow
for a high degree of certainty about tumor type and for localization before radiation therapy, improve the owner's ability
to make decisions regarding care, and enable the veterinarian to more accurately advise owners regarding therapy and prognosis.
Computerized tomographic findings for brain tumors are:
- Meningiomas are usually broad-based, peripherally located masses that were enhanced homogeneously with contrast material.
- Among the brain parenchymal tumors, astrocytomas are not distinguished easily from oligodendrogliomas because both tumors
have similar tomographic features of ring-like and nonuniform enhancement, and poorly defined tumor margins.
- Choroid plexus tumors are seen as well-defined, hyperdense masses that have marked uniform contrast enhancement.
- Pituitary tumors are distinguished readily by their location, minimal peritumoral edema, uniform contrast enhancement and
- In addition to defining primary brain tumors, computerized tomography may be helpful in identifying nasal tumors that have
extended into the rostral cerebrum. These dogs may have no clinical signs of nasal disease. magnetic resonance imaging is
optimal for demonstrating the amount of nasal or cerebral involvement and shows detailed anatomic features of these brain
Secondary tumor effects
Control of secondary tumor effects, such as increased intracranial pressure or cerebral edema, and tumor eradication (or reduction)
are the primary therapy for an intracranial tumor. Palliative therapy for dogs with brain tumors consists of the administration
of glucocorticoids for reducing edema, and in some cases, for retarding tumor growth.
Some animals with brain tumors demonstrate dramatic improvement in clinical signs for weeks or months with sustained glucocorticoid
Should seizure therapy be needed, phenobarbital is the drug best suited for control of generalized seizures. Eradication or
reduction of a brain tumor is the primary consideration for the long-term survival of a dog with a brain tumor. Therapy for
a brain tumor may include surgery, irradiation, chemotherapy, and immunotherapy (biologic response modification).
Palliative therapy for brain tumors is administration of glucocorticoids. Glucocorticoids readily penetrate the blood-brain
barrier and have some direct antitumor activity. Dexamethasone is preferred in acute and severe cases, whereas prednisone
or prednisolone may be used for maintenance.
Brain tumors of any histopathologic type or location always carry a poor prognosis. Most dogs with brain tumors eventually
die or are euthanized as a direct result of their tumor.