What is structural epilepsy?

Structural epilepsy is seizures caused by an identifiable physical abnormality in the brain. Unlike idiopathic epilepsy — where the brain appears structurally normal — structural epilepsy has a detectable cause that can be seen on MRI or identified through cerebrospinal fluid (CSF) analysis. The distinction matters enormously because structural epilepsy often requires treatment directed at the underlying cause, not just seizure control with anti-seizure medication.

Common causes of structural epilepsy

Brain tumors (intracranial neoplasia)

Brain tumors are among the most common causes of structural epilepsy in older dogs and cats. The most frequently encountered brain tumors in dogs include meningiomas (arising from the membranes surrounding the brain) and gliomas (arising from brain tissue itself). In cats, meningiomas are particularly common and frequently amenable to surgical treatment.

New onset seizures in a dog or cat over 6–7 years of age should prompt thorough investigation for a brain tumor. This does not mean every older pet with a first seizure has a tumor — but age is an important risk factor that changes the diagnostic probability.

Inflammatory brain disease (encephalitis)

Inflammation of the brain — encephalitis — is an important cause of structural epilepsy in dogs particularly. Several distinct inflammatory brain conditions are recognized in veterinary neurology:

• Necrotizing meningoencephalitis (NME) — An immune-mediated inflammatory condition seen most commonly in small breeds including Pugs, Chihuahuas, Maltese, and Shih Tzus. Also called Pug dog encephalitis (PDE) in that specific breed.
• Granulomatous meningoencephalomyelitis (GME) — Another immune-mediated inflammatory condition affecting dogs of various breeds
• Necrotizing leukoencephalitis (NLE) — Similar to NME; seen in Yorkshire Terriers and French Bulldogs among others
• Infectious encephalitis — Caused by viruses (distemper), bacteria, fungi (cryptococcosis), or parasites (Toxoplasma, Neospora)

Vascular disease (strokes)

Ischemic stroke — the veterinary equivalent of a human stroke — can cause structural brain lesions that subsequently produce seizures. Hemorrhagic stroke (bleeding into the brain) can also cause seizures. Strokes in pets are often associated with underlying conditions including hypertension, Cushing's disease, hypothyroidism, and kidney disease.

Trauma

Head trauma can cause seizures both acutely and as a late-onset complication weeks to months after the injury. Pets with a history of significant head trauma who develop seizures should be assessed with this history in mind.

How structural epilepsy is diagnosed

MRI is the primary tool for identifying structural brain disease. CSF analysis is typically performed alongside MRI when inflammatory or infectious causes are suspected. Together, these tests can usually characterize the nature of the structural abnormality and guide treatment planning.

Treatment approach

Treatment of structural epilepsy typically has two components:

• Anti-seizure medication — To control seizures while the underlying cause is addressed
• Treatment of the underlying cause — Which varies significantly depending on the diagnosis:

• Brain tumors may be treated with surgery (particularly meningiomas in cats), radiation therapy, or palliative management
• Immune-mediated encephalitis is treated with immunosuppressive medications, typically including corticosteroids
• Infectious encephalitis is treated with appropriate antimicrobial, antifungal, or antiparasitic medications
• Vascular disease is managed by treating underlying conditions (hypertension, endocrine disease) and supportive care

Prognosis

Prognosis in structural epilepsy is highly variable and depends on the underlying cause, the extent of brain involvement, and the response to treatment:

• Meningiomas in cats — Often surgically resectable with good long-term outcomes; median survival times of over 2 years reported with surgery
• Gliomas in dogs — More guarded prognosis; less amenable to surgery; radiation therapy may extend survival
• Immune-mediated encephalitis — Variable; some dogs respond well to long-term immunosuppression; others are more difficult to control
• Ischemic stroke — Many pets show meaningful recovery over weeks to months; prognosis depends on the underlying cause