Feline Meningioma

Feline meningioma is the most common primary brain tumor in cats, arising from the meninges — the protective membranous layers surrounding the brain and spinal cord [2][7]. These tumors predominantly affect older cats, with a reported mean age of onset of approximately 12.5 years [7]. While most feline meningiomas are histologically classified as benign, they can produce significant neurological deficits through mass effect, brain compression, and, in rarer cases, direct parenchymal invasion [1][4]. Unlike their human counterparts, feline meningiomas are often well-circumscribed and amenable to surgical resection, though recurrence and atypical behavior remain important clinical considerations [5].

The precise etiology of feline meningioma remains incompletely understood, but the following factors and mechanisms are recognized:

Cell of Origin Meningiomas arise from meningothelial (arachnoid cap) cells of the leptomeninges. These cells line the arachnoid membrane and serve normally as a structural barrier; neoplastic transformation leads to uncontrolled proliferation forming a discrete or multinodular mass [2][7].

Epidemiology and Risk Factors There is no statistically significant sex predilection in cats [7]. Advanced age is the strongest risk factor, with a mean age of 12.5 years at diagnosis (range 6–21 years) [7]. No definitive genetic mutations analogous to human NF2 mutations have been confirmed in feline meningiomas, though molecular pathways continue to be investigated.

Anatomical Predilection Tumors most commonly develop in the supratentorial compartment (cerebral convexities, falx cerebri) but can occur in the posterior fossa, including the cerebellum [1][7]. Spinal meningiomas also occur, and differentiating these from peripheral nerve sheath tumors (PNSTs) can be histopathologically challenging [8].

Histological Subtypes and Tumor Microenvironment Multiple histological subtypes are recognized, including fibrous, meningothelial, transitional, psammomatous, and others [7]. Immunohistochemical studies show that intracranial meningiomas in cats are reliably immunoreactive for E-cadherin but not for S100 or GFAP, markers that help distinguish them from PNSTs and glial tumors [8]. Saito et al. also demonstrated expression of cytokeratin and cell adhesion molecules in feline meningioma tissue [7].

Immune Microenvironment Although feline meningiomas are classified as benign by histological criteria alone, their tumor microenvironment is not immunologically inert. Immune cell infiltration — including lymphocytes and macrophages — has been documented, paralleling findings in human and canine meningiomas, though the functional significance of this infiltrate in cats remains to be fully characterized [2].

Somatostatin Receptor Expression Feline meningiomas have been shown to express somatostatin receptors (SSTRs), an important finding because synthetic somatostatin analogues are used therapeutically in humans with SSTR-expressing tumors. This opens potential avenues for adjunctive medical management in cats [5].

Brain Invasion Although the vast majority of feline meningiomas behave in a locally expansive rather than invasive fashion, direct parenchymal invasion has been documented in histologically benign tumors, creating a clinically significant discordance between histological grade and biological behavior [1].

Rare Variants and Differentials Meningioangiomatosis (MA) — a rare meningovascular proliferative entity distinct from conventional meningioma — has been described in cats and should be considered as a differential, particularly in cases with atypical MRI or gross pathological findings [6].

Clinical and Neurological Examination A thorough neurological examination establishes lesion localization (forebrain, cerebellum, brainstem, or spinal cord) and guides imaging choices. Findings such as circling, postural reaction deficits, and cranial nerve abnormalities help direct suspicion toward intracranial disease [1][7].

Advanced Imaging

• ·Magnetic Resonance Imaging (MRI): MRI is the gold standard for diagnosis. Feline meningiomas classically appear as extra-axial, well-defined masses. They are typically isointense on T1-weighted sequences, variable on T2/FLAIR sequences, and show marked, homogeneous contrast enhancement [4]. A "dural tail" sign — enhancement of the adjacent dura — may be present. MRI also reveals mass effect, perilesional edema, and any evidence of parenchymal invasion [1][4].
• ·Computed Tomography (CT): CT is valuable for evaluating bony involvement, particularly when nasal or cribriform plate destruction is suspected [4]. CT can detect hyperostosis of the overlying skull and mineralization (psammoma bodies) within the tumor. CT is also used to screen for metastatic disease [1].

Histopathology Definitive diagnosis requires tissue sampling. Histopathological examination remains the gold standard for confirming the diagnosis, identifying subtype, and assessing for features of malignancy or invasion. Key features include characteristic whorling patterns, psammoma body formation, and specific immunohistochemical profiles [7].

Immunohistochemistry (IHC) IHC is especially valuable for distinguishing meningioma from histological mimics:

• ·E-cadherin: Positive in feline intracranial meningiomas; helps differentiate from PNSTs [8]
• ·S100 and GFAP: Typically negative in meningioma; positive in PNSTs and glial tumors, respectively [8]
• ·Cytokeratin: Expression has been documented in feline meningioma and can assist in differential diagnosis [7]
• ·Somatostatin receptors (SSTRs): Expression has been confirmed in feline meningiomas, potentially relevant for future targeted therapy stratification [5]

Laboratory Diagnostics There are no pathognomonic serum biochemistry or hematological changes specific to meningioma. However, a full diagnostic workup should include:

• ·Complete Blood Count (CBC): Assess for anemia (low HCT/PCV), leukocytosis (elevated WBC) suggesting paraneoplastic or infectious processes, and thrombocytopenia (low PLT)
• ·Serum Biochemistry Panel: Evaluate hepatic function (ALT, TBIL), renal function (BUN, CREA), and protein levels (ALB, GLOB) to assess overall health status and anesthetic risk prior to surgery
• ·Urinalysis: Part of baseline staging and pre-anesthetic assessment
• ·Thoracic radiographs: To rule out primary pulmonary neoplasia with intracranial metastasis and to assess cardiopulmonary fitness for anesthesia

Cerebrospinal Fluid (CSF) Analysis CSF analysis may reveal elevated protein and a mild mononuclear pleocytosis, but findings are nonspecific. CSF cytology is rarely diagnostic for meningioma and carries the risk of cerebral herniation if intracranial pressure is significantly elevated; it should be performed with caution.

Surgical Resection Surgery remains the primary and most effective treatment for feline meningioma. Craniotomy with gross total or subtotal tumor resection is the treatment of choice for accessible supratentorial and posterior fossa lesions [1][7]. Cats tolerate craniotomy relatively well compared to dogs, and excellent outcomes have been reported in appropriate surgical candidates. However, parenchymal invasion — even in histologically benign tumors — may preclude complete excision, as demonstrated in a reported case of cerebellar meningioma requiring only subtotal resection due to tumor infiltration into brain parenchyma [1].

Radiation Therapy Radiation therapy (RT) is indicated as a primary treatment when surgery is not feasible, or as adjuvant therapy following incomplete surgical resection. Modern approaches, including stereotactic radiosurgery (SRS) and fractionated stereotactic radiation therapy (FSRT), offer precise tumor targeting while minimizing damage to surrounding tissue. Novel delivery systems and treatment planning continue to evolve in veterinary neuro-oncology [3]. RT is particularly relevant for recurrent tumors or cases where residual disease is suspected post-operatively [5].

Combined Surgery and Radiation Combined surgical debulking followed by radiation therapy may extend disease-free intervals compared to either modality alone, particularly in cases of subtotal resection [5].

Medical / Pharmacological Management

• ·Corticosteroids (e.g., prednisolone/dexamethasone): Used perioperatively and palliatively to reduce peritumoral edema and alleviate neurological signs. They are not curative but can meaningfully improve quality of life.
• ·Anticonvulsants (e.g., phenobarbital, levetiracetam): Indicated for cats presenting with seizures.
• ·Somatostatin Analogues: The demonstration of SSTR expression in feline meningiomas raises the possibility of adjunctive treatment with synthetic somatostatin analogues (e.g., octreotide, pasireotide), an approach used in human meningioma. This remains investigational in cats but represents a promising avenue for future targeted therapy [5].
• ·Novel Therapies: Nanocarriers, molecularly targeted agents, immunotherapy, and other biologic approaches are being explored across veterinary neuro-oncology platforms. Shared molecular and genetic pathways between feline, canine, and human brain tumors are being leveraged to accelerate drug development and translation [3].

Palliative Care For cats that are not surgical candidates due to advanced age, comorbidities, or tumor location, a palliative approach — combining corticosteroids, anticonvulsants, and supportive nursing care — can maintain acceptable quality of life for weeks to months.

Feline meningioma carries a generally favorable prognosis relative to other intracranial tumors, particularly when complete surgical resection is achieved. Key prognostic considerations include:

Post-Surgical Outcomes Published case series and retrospective studies indicate that cats undergoing surgical resection of meningioma can achieve median survival times of approximately 26 months or greater, with some individuals surviving several years post-operatively. This is markedly better than most other primary brain tumors and is one of the most favorable surgical oncology outcomes in veterinary neurology.

Impact of Histological Subtype and Invasion While most feline meningiomas are histologically benign, the discovery of parenchymal brain invasion — even in otherwise benign tumors — significantly complicates surgical management and is associated with a higher likelihood of incomplete resection and subsequent recurrence [1]. The discordance between benign histological appearance and invasive biological behavior underscores the importance of complete resection and post-operative surveillance imaging.

Recurrence Tumor recurrence is a recognized outcome following both surgery and radiation therapy; standard treatment options do not reliably prevent recurrence or progression in all cases, motivating ongoing research into adjunctive therapies including somatostatin analogues and other novel agents [5].

Atypical Presentations Cases with extensive extracranial invasion (e.g., nasal cavity and cribriform plate destruction) present unique surgical challenges, and the prognosis in such cases is more guarded due to the complexity of achieving tumor-free margins [4].

Rare Variants Meningioangiomatosis, a rare and distinct meningovascular entity, can carry a grave prognosis in cases presenting with acute, severe neurological decompensation, as evidenced by a reported feline case that died within 5 days of acute deterioration [6].

Overall For the typical older cat with a solitary, surgically accessible, histologically benign meningioma diagnosed on MRI and managed with surgical resection ± radiation, the prognosis is good to excellent with appropriate perioperative care. Quality of life post-surgery is generally reported as good in successful cases. Long-term prognosis is more guarded for incompletely resected, recurrent, or invasive tumors.

There are currently no known preventive measures for feline meningioma. Because the etiology involves spontaneous neoplastic transformation of meningothelial cells in aging cats, and no definitive causative infectious agent, dietary factor, or environmental toxin has been identified, targeted prevention is not currently possible.

Recommendations for Cat Owners and Veterinarians:

• ·Regular veterinary wellness examinations in senior and geriatric cats (ideally every 6 months for cats over 10 years) allow for early detection of subtle neurological changes that may prompt timely imaging.
• ·Neurological monitoring: Owners of older cats should be counseled on early warning signs such as behavior change, gait abnormalities, and new-onset seizures, facilitating earlier diagnosis and intervention.
• ·No vaccine exists for meningioma, and there is no established chemoprevention protocol in veterinary medicine.
• ·Genetic screening is not currently available or validated for this tumor in cats.

Research into the tumor microenvironment [2], receptor expression profiles [5], and comparative oncology models [3] may eventually uncover targetable predisposing mechanisms, but prevention strategies remain a future aspiration rather than a current clinical reality.