Edema of the brain in a dog

Richard A. LeKouture, Bachelor of Veterinary Science, PhD, ACVIM Diploma (Neurology), ECVN Diploma University of California Davis CA 95616 USA

The most common in dogs are meningiomas andglioma. Most primary brain tumors are single, but there are reports of multiple primary brain tumors. Secondary, or metastatic, tumors are less common and can be the result of the growth and spread of a local tumor (nasal adenocarcinoma) or metastases of primary tumors elsewhere. Skull tumors can affect the brain when spreading a local tumor. Although brain tumors are found in dogs of all breeds, both sexes and at any age, incidence of tumors increases at the age of five, as well as in certain breeds. Glial cell tumors and pituitary tumors are commonly found in brachycephaly, while meningiomas are most common in dolichocephalans.

Primary brain tumors arise fromcells, which are usually found inside the brain and meninges. Secondary tumors are a metastasis that develops from a primary tumor that is located outside the nervous system or appears by local invasion of adjoining tissues that are not related to the nerve (for example, bone tissue). Neoplasms of the pituitary gland and tumors arising from the cranial nerves are considered secondary tumors of the brain.
Tumors of the brain are the causecerebral dysfunction due to infiltration of healthy brain tissue, compression of adjacent structures, disruption of cerebral blood circulation and local necrosis. Secondary effects of brain tumors include hydrocephalus, an increase in intracranial pressure, cerebral edema and a hernia of the brain. Primary brain tumors grow usually slowly, and the brain adapts to a slow increase in intracranial pressure. During this period of compensation, there may be indistinct symptoms and small changes in behavior. Even with a slowly progressing tumor, clinical signs can develop rapidly when the compensatory mechanisms are depleted. With rapidly growing tumors, the same degree of compensation is impossible, and therefore severe neurologic dysfunction may suddenly appear in the absence of prodromal signs.

Case history and clinical signs.

Neurological signs arising inthe result of a brain tumor, mainly depends on the location, size and growth rate of the tumor mass. Many dogs and cats can be observed indefinite signs such as: unwillingness to be kept on hand, trying to hide during the day, reducing the frequency of purring or level of activity. Usually, focal or generalized seizures are noted.

Focal neurological symptoms usually servea sign of a significantly developed tumor. Neoplasms involving the brain stem can lead to abnormalities of the cranial nerves. Weakness and sensory disturbances are often observed in lesions in the cerebral forehead areas or their deep paths. Visual disturbances can accompany the development of tumors that affect the visual pathways from the occipital lobe of the brain to the optic nerve. Hearing loss is noted when a cerebellar medullary region, a brainstem or temporal lobes of the brain are affected. Reducing the ability to smell can be observed with damage to the trellis plate or olfactory bulbs, as well as other rhinocephalic compounds. Violations of balance or gait mean damage to the cerebellum or vestibular apparatus.

Secondary effects of brain tumorsinclude increased intracranial pressure and cerebral edema. Clinical symptoms include: changes in behavior (eg, lethargy, irritability), maneuvers, squeezing of the head, involuntary walking, alteration of the state of consciousness or associated locomotor disorders. Most dogs or cats with a brain tumor are observed in the veterinarian due to problems associated with the side effect of the tumor.

Based on signs, medical history andresults of a complete physical and neurological examination, it is possible to determine the localization of a disorder in the brain and in some cases to establish its approximate finding. Symptoms of the disease for a given localization in the nervous system will be similar regardless of the exact cause. In order to exclude other categories of the disease, it is necessary to adhere to a consistent diagnostic plan. The minimum data from these patients should include: hemogram, chemical analysis of serum, urine analysis, chest x-ray and peritoneal ultrasound. Although simple skull X-rays are of limited value in diagnosing a primary brain tumor, their use can facilitate the detection of neoplasm of the skull or nasal cavity. Occasionally lysis or hyperstrosis of the skull may accompany the primary brain tumor (eg, meningioma of cats), or on the roentgenogram, mineralization within the neoplasm can be seen. General anesthesia is necessary for accurate positioning of the skull for carrying out radiography.

Analysis of cerebrospinal fluid is recommendedto conduct in order to help eliminate inflammatory diseases and promote the diagnosis of a brain tumor. Care should be taken when collecting cerebrospinal fluid, because intracranial pressure often increases, and pressure changes associated with the drainage of the cerebrospinal fluid can lead to a hernia of the brain. Hyperventilation or administration of mannitol before the collection of cerebrospinal fluid will help reduce intracranial pressure. An increase in the protein content in the cerebrospinal fluid and the white blood cell content is normal or elevated - these symptoms are considered a typical sign of brain neoplasm, although often the composition of cerebrospinal fluid may not change. Neoplastic cells can be present in the cerebrospinal fluid, especially when precipitation methods are used for analysis.
Computer tomography and magnetic resonance giveaccurate information about the presence, location and size of intracranial neoplasms. Images of magnetic resonance give a more accurate picture than computed tomography, when studying certain areas of the brain (for example, the brain stem). Meningiomas are difficult to detect with magnetic resonance without the use of contrast medium. Meningioma can have a "speckled" appearance and surface, it is often located between the tumor and surrounding tissue of the brain at the stage of tumor development T1 and T2. A hypointense signal can indicate compression of the arachnoid plate, as well as compression of the venous plexus. Hypointense zones inside the meningioma may indicate intracellular mineralization. The "dural tail" symptom is not necessarily specific for meningioma, but is often caused by neoplastic infiltration of the meningiomas outside the margins of the meningioma or by hypervascularization of the hard shell. It is advisable to perform a biopsy of intracranial lesion before the start of therapy, but a biopsy is not always used because of the high cost of it, as well as an increase in the incidence of animals. Lesions that are not of a neoplastic nature and occupy a large space can mimic the appearance of neoplasm in CT or magnetic resonance imaging, and metastasis may resemble a primary brain tumor. Currently, biopsy is the only method used for the final diagnosis of a brain tumor. Known methods of biopsy include biopsy under the supervision of ultrasound, as well as computed tomography. Stereotactic biopsy control systems using computed tomography provide a relatively non-invasive, rapid and very accurate biopsy of a tumor with a low degree of complications.

Cytological evaluation of specimens during biopsya brain tumor can be done within a few minutes while examining the crushed drugs. Samples of the tissue are quickly fixed in 95% alcohol and are stained with hematoxylin and eosin. Accurate information using this rapid method, as a rule, can be obtained with primary and metastatic tumors of the nervous system and lesions that are not of a neoplastic nature. Air-dried slides with fixed crushed preparations can also be painted with Wright's and Giemsa's colors to obtain additional information on the composition of cells in the tumor.

Objectives of brain tumor therapy - eliminationa tumor (or a decrease in its size) and control of side effects (eg, increased intracranial pressure or cerebral edema). Palliative therapy of animals with a brain tumor consists of glucocorticoids to reduce edema and, in some cases (for example, with lymphoma), is necessary to slow the growth of the tumor. When treating seizures, phenobarbital should be used - this drug is most suitable for controlling already generalized seizures.

The role of surgical treatment has increased in the treatmentintracranial neoplasm in cats or dogs. The exact location, size and type of neoplasm determine how much it is to be removed. Meningiomas, especially those that are located above the frontal lobes of the brain, can often be removed, especially in cats. On the contrary, morbidity and mortality associated with surgical removal of the caudal fossa and neoplasm of the brain stem are significantly increased. Partial removal of brain neoplasm can reduce the symptoms of cerebral dysfunction, provide a histological diagnosis and can allow the preparation of an animal for another type of therapy, such as irradiation. Surgical biopsy of the tumor should be approached with caution in order to avoid the spread of tumor cells to healthy tissue.

The use of irradiation in the treatment of primarybrain tumors in dogs and cats gives good results, and can be used alone or in combination with other methods of treatment. External irradiation and current megavoltage exposure are recommended for therapy of brain tumors in dogs and cats. Despite the fact that orthovolt radiation is used, it is not an optimal method of treatment due to weak penetration of the beam and configuration with a limited field. It is important that the radiation therapist carefully planned the treatment. When choosing the dose of irradiation take into account the type of tumor, its localization, as well as the tolerance of surrounding healthy tissues.