🧠 Herniated Arachnoid Pouch

A herniated arachnoid pouch is a focal outpouching of the arachnoid membrane through a dural defect, typically seen in the spine. It is most often associated with lateral dural tears and spontaneous intracranial hypotension (SIH).

🔬 Pathophysiology The arachnoid membrane (the middle meningeal layer) herniates through a tear in the dura mater, often at the lateral aspect of a spinal nerve root sleeve.

This creates a pouch-like extension filled with cerebrospinal fluid (CSF), which may interfere with healing or prevent effective sealing by an epidural patch.

📸 Imaging Best visualized on spine MRI or dynamic CT myelography

Often seen as a CSF-intensity structure adjacent to the spinal dura or nerve root sleeve

May co-occur with spinal longitudinal extradural CSF collection (SLEC)

⚠️ Clinical Relevance Commonly associated with CSF leaks and SIH symptoms (e.g., orthostatic headache)

In this study, its presence was associated with lower success rates of radiologic resolution after epidural patching

May require surgical repair in refractory cases