**Question:** CSF is absorbed by -

A. Arachnoid villi
B. Virchow-Robinson's spaces
C. Virchow's node
D. Subarachnoid spaces

**Core Concept:**

The cerebrospinal fluid (CSF) is a clear, colorless fluid that surrounds and protects the brain and spinal cord. It plays a crucial role in maintaining the brain's osmotic pressure, removing waste products, and providing a cushion during movements. CSF is produced in the choroid plexus of the ventricles and circulates through the ventricles before draining into the subarachnoid space surrounding the brain and spinal cord.

**Why the Correct Answer is Right:**

CSF is primarily absorbed through two main pathways:

1. **Arachnoid villi (Option A):** These are finger-like projections of the arachnoid membrane located at the foramen of Monro, between the lateral ventricles, and at the junction of the fourth ventricle and aqueduct of Sylvius. Arachnoid villi have fenestrated capillaries, allowing CSF proteins and cells to enter the bloodstream, while maintaining CSF homeostasis.

2. **Virchow-Robinson's spaces (Option B):** These are the spaces between the arachnoid and pia mater membranes, which are continuous with the subarachnoid spaces. CSF enters Virchow-Robinson's spaces and is absorbed into the systemic circulation via the meningeal lymphatics, which in turn drain into the cervical lymph nodes.

**Why Each Wrong Option is Incorrect:**

3. **Virchow's node (Option C):** This is a misnomer, as Virchow-Robinson's spaces and arachnoid villi are responsible for CSF absorption, not Virchow's node. Virchow's node is a lymph node located in the mediastinum, not involved in CSF absorption.

4. **Subarachnoid spaces (Option D):** While subarachnoid spaces are where CSF circulates, they are not directly involved in CSF absorption. CSF enters Virchow-Robinson's spaces before being absorbed into the systemic circulation.

**Clinical Pearl:**

Understanding the pathways of CSF absorption is crucial for understanding the pathophysiology of conditions like subarachnoid hemorrhage, meningitis, and hydrocephalus, as well as the effects of medications and interventions targeting CSF dynamics.