Most common cancer that metastasizes to leptomeninges :
**Core Concept**
The leptomeninges, consisting of the pia and arachnoid membranes, are the most common site for metastatic spread from systemic cancers. This phenomenon is typically observed in highly malignant tumors with a propensity for hematogenous dissemination.
**Why the Correct Answer is Right**
The most common cancer to metastasize to the leptomeninges is small cell lung cancer (SCLC). This aggressive tumor type is known for its rapid growth and early metastasis, often involving the central nervous system (CNS). SCLC cells can disseminate through the bloodstream and seed in the leptomeninges, leading to symptoms such as headache, cranial nerve palsies, and altered mental status. The involvement of the leptomeninges can be diagnosed using imaging studies like MRI or CT scans, which show enhancement of the meninges.
**Why Each Wrong Option is Incorrect**
**Option A:** Breast cancer is a common malignancy, but it is not the most common cancer to metastasize to the leptomeninges. Breast cancer metastases to the CNS are more commonly seen in the brain parenchyma rather than the leptomeninges.
**Option B:** Melanoma is a highly aggressive skin cancer with a propensity for CNS metastasis. However, it is less common than SCLC to metastasize to the leptomeninges.
**Option C:** Glioblastoma is a primary brain tumor, not a metastatic cancer. It arises from the brain parenchyma and does not typically metastasize to the leptomeninges.
**Clinical Pearl / High-Yield Fact**
When encountering a patient with symptoms suggestive of leptomeningeal metastasis, such as headache, cranial nerve palsies, or altered mental status, it is essential to consider SCLC as a potential underlying cause. A high index of suspicion and prompt imaging studies can lead to timely diagnosis and treatment.
**Correct Answer:** C.