Brain Tumors Clinical Primer

Introduction

A brain tumor is any intracranial neoplasm, a mass of abnormal cells growing within the cranial cavity. These tumors are broadly categorized as either primary, originating from the brain tissue or its immediate surroundings, or secondary (metastatic), originating from cancers elsewhere in the body. The clinical course varies widely; primary tumors often develop slowly over months or years, whereas metastatic disease can progress rapidly. Prognosis is determined by a combination of the tumor’s pathological type, grade, molecular characteristics, and its specific location, which can limit treatment options even for histologically benign tumors.

Classification and Key Concepts

The World Health Organization (WHO) classification of Central Nervous System (CNS) tumors underwent a paradigm shift in 2016, moving from a purely histological diagnosis to an integrated approach that incorporates molecular and genetic information. This allows for more accurate prognostication and guides targeted therapies.

Brain tumors can arise in any part of the CNS, most commonly in the cerebral hemispheres, but also in the sella turcica, cerebellum, brainstem, and ventricles.

I. Common Primary Brain Tumors

Primary brain tumors arise from the diverse cell populations within the CNS.

A. Gliomas (Neuroepithelial Tumors)

Gliomas are the most common type of primary malignant brain tumor, originating from the glial (supportive) cells of the brain.

| Type | Key Features |
| :— | :— |
| Diffuse Astrocytic & Oligodendroglial Tumors | A spectrum of tumors. Astrocytomas are often lower-grade and slow-growing. Glioblastoma is the most common and most aggressive primary brain tumor in adults, characterized by rapid, infiltrative growth and a poor prognosis. Oligodendrogliomas are typically slower-growing and more defined. |
| Medulloblastoma | A highly malignant embryonal tumor, most commonly found in the cerebellum of children. It can obstruct cerebrospinal fluid (CSF) flow, leading to hydrocephalus. |

B. Meningiomas

• Origin: Arise from the meninges, the membranes surrounding the brain and spinal cord.
• Prevalence: Account for about 20% of primary brain tumors.
• Characteristics: Typically benign and slow-growing with clear borders. They often grow on the brain’s surface, along the sagittal sinus, or at the skull base. They can cause erosion or reactive proliferation of the adjacent skull bone.

C. Pituitary Adenomas

• Origin: Benign tumors arising from the cells of the anterior pituitary gland.
• Prevalence: Comprise about 10% of intracranial neoplasms.
• Classification: Often categorized by the hormone they secrete:
  • Prolactinomas (PRL tumors): Secrete prolactin.
  • Growth Hormone (GH) Adenomas: Cause acromegaly.
  • ACTH-secreting Adenomas: Cause Cushing’s disease.
  • Non-secreting adenomas: Cause symptoms by mass effect on surrounding structures like the optic chiasm.

D. Nerve Sheath Tumors

• Acoustic Neuroma (Vestibular Schwannoma): A benign tumor originating from the Schwann cells of the vestibular nerve (CN VIII).
• Prevalence: Accounts for about 10% of brain tumors.
• Clinical Features: Classic presentation includes progressive sensorineural hearing loss, tinnitus, and vestibular dysfunction. Larger tumors can compress the adjacent trigeminal (CN V) and facial (CN VII) nerves and the cerebellum.

E. Other Common Primary Tumors

• Craniopharyngioma: A benign, cystic tumor arising from epithelial remnants of Rathke’s pouch, typically located near the pituitary stalk.
• Prevalence: More common in children and adolescents.
• Clinical Features: Due to its location, it often causes visual impairment (bitemporal hemianopsia), endocrine dysfunction (diabetes insipidus, growth delay), and obesity.

II. Secondary (Metastatic) Brain Tumors

• Prevalence: Metastatic brain tumors are more common than primary brain tumors. Autopsy studies find brain metastases in up to 25% of cancer patients.
• Origin: Malignant cells travel to the brain via the bloodstream (hematogenous spread).
• Common Primary Sites: The most common cancers that metastasize to the brain are:
  1. Lung Cancer (most frequent)
  2. Breast Cancer
  3. Melanoma
  4. Renal Cell Carcinoma
  5. Colorectal Cancer
• Characteristics: Lesions are often multiple and located at the grey-white matter junction. They are a major cause of morbidity and mortality in cancer patients and carry a poor prognosis.

Management Principles

• Benign Tumors: Complete surgical resection can be curative.
• Borderline/Malignant Tumors: Management requires a multidisciplinary approach. Surgery is often the first step, followed by a combination of radiotherapy and chemotherapy. Newer modalities like immunotherapy, targeted molecular therapy, and stereotactic radiosurgery are increasingly used based on the tumor’s specific pathology and genetic profile.

Conclusion

Brain tumors are a heterogeneous group of diseases with diverse pathologies and clinical outcomes. The integration of molecular data into classification has revolutionized diagnosis and treatment, paving the way for more personalized and effective management strategies.