What is the Insula?
The insula, or insular cortex, is a deeply located region of the brain, nestled within the Sylvian fissure (also called the lateral sulcus), hidden beneath parts of the frontal, temporal, and parietal lobes. Although not visible from the brain’s surface, the insula plays essential roles in autonomic regulation, interoception, emotion, taste, language, motor control, and pain perception.
Due to its central location and proximity to critical structures like the internal capsule, basal ganglia, and language/motor areas, tumors in the insular region present a unique challenge in neurosurgical oncology. However, modern advancements in imaging, mapping, and awake brain surgery have significantly improved their management.
What Are Insular Tumors?
Insular tumor are neoplastic lesions originating within or infiltrating the insular area of brain. Most of these tumors are derived from glial cells. Their clinical presentation often includes drug-resistant epilepsy, aphasia, or cognitive slowing, depending on the tumor’s size, grade, and hemispheric location (dominant vs. non-dominant hemisphere).
Histopathological and Molecular Subtypes of Insular Tumors
The classification of insula tumor aligns with the World Health Organization (WHO) system for central nervous system tumors, which integrates both histological grading and molecular markers. The most common types of tumors encountered in the insula include:
1. Astrocytic Tumors
These tumors arise from astrocytes and can range from low- to high-grade lesions:
Pilocytic Astrocytoma (WHO Grade 1): Rare in the insula; more common in children; often associated with BRAF mutations.
Diffuse Astrocytoma, IDH-mutant (WHO Grade 2): Slow-growing and infiltrative; often presents with seizures; typically affects young adults.
Anaplastic Astrocytoma, IDH-mutant (WHO Grade 3): More cellular with increased mitotic activity; behaves more aggressively.
Glioblastoma, IDH-wildtype (WHO Grade 4): The most malignant and rapidly progressive glioma; frequently presents with neurologic decline and mass effect.
2. Oligodendroglial Tumors
These are glial tumors characterized by the presence of both IDH mutations and 1p/19q codeletion, which are essential for the diagnosis:
Oligodendroglioma, IDH-mutant, 1p/19q-codeleted (WHO Grade 2): Typically slow-growing; highly associated with long-term survival and better response to therapy.
Anaplastic Oligodendroglioma (WHO Grade 3): Faster growing with increased mitoses and microvascular proliferation.
3. Glioneuronal Tumors
Less common in the insular region but should be considered, especially in children and young adults presenting with epilepsy:
Ganglioglioma: A mixed glial-neuronal tumor; may present with drug-resistant focal seizures.
DNET (Dysembryoplastic Neuroepithelial Tumor): Often cortical-based but may extend to the insula; benign and strongly associated with epilepsy.
4. Other Rare Tumors
Although uncommon, the insula can also be the site of:
Ependymomas
Metastases
Primary CNS lymphomas
Vascular malformations (e.g., cavernomas mimicking tumors)
Diagnosis and Imaging
The diagnosis of insular tumors relies on advanced neuroimaging techniques:
MRI with contrast is the gold standard for localization, tumor extension, and edema assessment.
Magnetic Resonance Spectroscopy (MRS) helps distinguish low-grade from high-grade lesions based on metabolic profiles.
PET imaging may aid in identifying high metabolic activity.
Functional MRI (fMRI) and Diffusion Tensor Imaging (DTI) are critical in surgical planning, particularly for mapping language and motor tracts.
Treatment Strategies for Insular Tumors
The management of insular tumors requires a multidisciplinary approach, integrating surgical, radiological, and pharmacological expertise.
1. Microsurgical Resection
Maximal safe resection remains the primary treatment.
2. Radiotherapy
Postoperative radiation is standard in high-grade tumors. Techniques like intensity-modulated radiotherapy (IMRT) and proton therapy are employed to preserve healthy tissue.
3. Chemotherapy
Temozolomide (TMZ) is one of the first line treatment modality for high-grade gliomas, especially glioblastomas, often administered with radiotherapy.
Alternative regimens like PCV (procarbazine, lomustine, vincristine) are used particularly in patients with oligodendrogliomas showing favorable molecular profiles.