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Intracranial Hypotension


KEY FACTS

Terminology

  • Headache caused by ↓ intracranial CSF pressure

Imaging

  • Classic imaging

    • Diffuse dural thickening/enhancement

      • –

        Smooth, not nodular or “lumpy-bumpy”

    • Downward displacement of brain through incisura (“slumping” midbrain)

    • Veins, dural sinuses distended

    • ± subdural hygromas/hematomas

  • Other: Midbrain elongated, ambient cisterns effaced on axial T2WI

Top Differential Diagnoses

  • Meningitis

  • Meningeal metastases

  • Chronic subdural hematoma

  • Dural sinus thrombosis

  • Postsurgical dural thickening

  • Idiopathic hypertrophic cranial pachymeningitis

Clinical Issues

  • Severe headache (orthostatic, persistent, pulsatile, or even associated with nuchal rigidity)

  • Uncommon: Cranial nerve palsy (e.g., abducens), visual disturbances

  • Rare: Severe encephalopathy with disturbances of consciousness

  • Profile: Young/middle-aged adult with orthostatic headache

Diagnostic Checklist

  • Only rarely are all classic findings of intracranial hypotension present in same patient

  • Do not misdiagnose intracranial hypotension as Chiari 1

    • Surgery can exacerbate symptoms

    • In rare cases can be fatal

Sagittal T2WI in a 57-year-old man treated for “migraine” headaches shows severe midbrain “slumping”
, downwardly displaced cerebellar tonsils
, draping of hypothalamus over dorsum sellae with mammillary bodies
below dorsum.

Sagittal T1 C+ FS MR in the same case shows the severe midbrain “slumping”
and inferiorly displaced tonsils. In addition, the pituitary gland appears “fat”
, and the dural venous sinuses are engorged
.

Axial T1 C+ FS scan in the same case shows a “fat” midbrain/pons
, prominent superior ophthalmic veins
, and engorged, outwardly convex transverse/sigmoid sinuses
. No subdural hematomas were identified. Severe intracranial hypotension was treated successfully with blood patch.

Axial T2WI in the same case shows the inferiorly displaced 3rd ventricle
superimposed on the compressed midbrain. The ambient cisterns
are completely effaced.

TERMINOLOGY

Abbreviations

  • Intracranial hypotension (IH)

Definitions

  • Headache caused by ↓ intracranial CSF pressure

IMAGING

General Features

  • Best diagnostic clue

    • Classic imaging quartet

      • –

        Downward displacement of brain through incisura (“slumping” midbrain)

      • –

        Diffuse dural thickening/enhancement

      • –

        Veins, dural sinuses distended

      • –

        Subdural hygromas/hematomas

    • Lack of 1 or more of 4 classic findings does not preclude diagnosis

  • Location

    • Pachymeninges (dura)

      • –

        Both supra- and infratentorial

      • –

        May extend into internal auditory canals

      • –

        Spinal dura, epidural venous plexuses may be involved

  • Morphology

    • Dural enhancement is smooth, not nodular or “lumpy-bumpy”

CT Findings

  • NECT

    • Relatively insensitive; may appear normal

    • Look for effaced suprasellar/basilar cisterns, “fat” midbrain/pons

    • ± thick dura

    • ± subdural fluid collections

      • –

        Usually bilateral

      • –

        CSF (hygroma) or blood (hematoma)

    • Atria of lateral ventricles may appear deviated medially, abnormally close (“tethered”) to midline

  • CECT

    • Diffuse dural thickening, enhancement

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