Spontaneous intracranial hypotension results from spinal CSF leakage and typically presents with orthostatic headache, although many patients have nonspecific symptoms, leading to frequent underdiagnosis. The estimated incidence of ~5 per 100,000 per year is likely underestimated due to limited clinical and radiologic recognition and the variable clinical presentations (1,2).

PATHOPHYSIOLOGY

According to the Monro–Kellie doctrine, the intracranial compartment maintains a fixed total volume of brain, CSF, and blood. When CSF volume decreases due to a spinal leak, compensatory expansion of the intracranial venous system occurs, being the most compliant component, resulting in the characteristic low-pressure imaging findings of SIH (6).

Fig 1: Figure A: Illustration of the normal Monro–Kellie doctrine, demonstrating the fixed intracranial volume relationship between brain parenchyma, cerebrospinal fluid (CSF), and intracranial blood. Figure B: Illustration depicting alterations in spontaneous intracranial hypotension (SIH), showing reduced CSF volume with compensatory increases in venous volume and formation of subdural collections in accordance with the Monro–Kellie principle.

Three main leak types are described based on the anatomical site and the presence or absence of an epidural fluid collection (3,4).

Secondary causes include dural injury from lumbar-puncture, spinal-anesthesia, spinal-surgery/trauma, or over-drainage following ventriculoperitoneal shunting (5).

Fig 2: The table summarizes the types of CSF leaks. Images A and B: Sagittal and axial T2-weighted images demonstrating a case of CSF leak with spinal longitudinal extradural collection (SLEC) (white arrows). Images C and D: Sagittal and axial T2-weighted images demonstrating a case of CSF leak without SLEC.