Spontaneous Intracranial Hypotension (Brain Sagging & Pachymeningeal Enhancement)

• Seen in young to middle-aged adults (peak age 30–50 years, female:male 2:1, strong association with underlying connective tissue disorders such as Marfan syndrome or Ehlers-Danlos syndrome) presenting with the pathognomonic clinical hallmark: severe, disabling Orthostatic (Postural) Headache. The headache develops or worsens markedly within 15–30 minutes of sitting or standing upright, and is dramatically relieved by lying completely flat (supine). Associated symptoms include neck stiffness, nausea, muffled hearing/tinnitus, and horizontal diplopia (cranial nerve VI palsy).
• Caused by chronic leakage of cerebrospinal fluid (CSF) through an occult structural tear in the spinal dural sac, resulting in low CSF volume and low CSF opening pressure (<6 cm H2O):
• (1)
  Spinal Dural Leak Etiologies:
• 1.
  Degenerative Spinal Osteophytes: Sharp calcified disc herniation or micro-osteophyte puncturing the ventral thecal sac (most common, 70%).
• 2.
  Meningeal Dural Diverticula: Rupture of a fragile perineural Tarlov cyst or nerve root sleeve diverticulum.
• 3.
  CSF-Venous Fistula (CVF): Direct, abnormal fistulous connection between the spinal subarachnoid space and adjacent epidural veins.
• (2)
  The Monro-Kellie Hypothesis: The total volume of the intracranial vault (brain, CSF, blood) is fixed. When CSF volume drops, intracranial venous structures and the meninges undergo massive compensatory venous engorgement and dural hypervascularity, causing diffuse pachymeningeal enhancement.

Imaging Findings

• Magnetic Resonance Imaging (Brain MRI - Diagnostic Gold Standard - The 'SEEPS' Framework):
• –
  S - Subdural Fluid Collections: Bilateral, symmetric, thin, crescentic subdural hygromas or chronic subdural hematomas (typically non-compressive, self-resolving with leak closure).
• –
  E - Engorgement of Venous Structures: Marked, prominent distension and rounding of the dural venous sinuses (especially the straight and transverse sinuses) on contrast T1WI.
• –
  E - Enhancement of Pachymeninges: Diffuse, continuous, uniform, non-nodular, smooth enhancement of the dura mater (pachymeninges) across the entire supratentorial and infratentorial brain, with strict sparing of the leptomeninges (pia/arachnoid).
• –
  P - Pituitary Hyperemia: Marked, symmetric, dome-like enlargement and intense enhancement of the pituitary gland, mimicking a pituitary macroadenoma.
• –
  S - Sagging of the Brain: Caudal downward displacement of the entire brainstem, flattening of the pons against the clivus, effacement of the suprasellar and prepontine cisterns, and downward tonsillar herniation through the foramen magnum mimicking a Chiari I malformation.
• –
  DWI / ADC: Bilateral subdural hygromas show free water diffusivity (no diffusion restriction), distinguishing them from subdural empyema (which shows intense diffusion restriction).
• –
  **SWI / T2* GRE: Demonstrates engorged dural venous sinuses, prominent cortical veins, and blooming blood products if tearing of bridging veins converts subdural hygromas into subdural hematomas**.
• Computed Tomography / MR Myelography (Spinal Leak Localization Gold Standard):
• –
  Dynamic CT Myelography / Digital Subtraction Myelography (DSM): The definitive gold standard to pinpoint the exact anatomical spinal CSF leak site or identify a subtle CSF-venous fistula for targeted therapy.

Differential Diagnosis

Important Points to Remember

• Diagnostic Pitfall: Diagnosing a Chiari I malformation or performing a surgical suboccipital decompression on a patient with brain sagging! Because the cerebellar tonsils herniate through the foramen magnum due to intracranial hypotension, patients are frequently misdiagnosed as congenital Chiari I malformations. Performing a posterior fossa surgical craniectomy/decompression on a patient with intracranial hypotension is catastrophic, causing rapid neurological collapse and death. Look for the SEEPS triad (dural enhancement, venous engorgement, subdural hygromas) to confirm intracranial hypotension.
• Crucial Review Areas:
• 1.
  Dura mater on post-contrast T1WI: diffuse, smooth, non-nodular pachymeningeal enhancement.
• 2.
  Cerebellar tonsils and brainstem: caudal descent with effacement of prepontine cistern (pons flattened against clivus).
• 3.
  Pituitary gland on sagittal T1: marked dome-like enlargement due to venous hyperemia.
• 4.
  Subdural space for bilateral symmetric hygromas or chronic subdural hematomas.
• Radiologist Safe Practice & Management:
• 1.
  Diagnostic Verification: Brain MRI with contrast plus whole-spine screening MRI to demonstrate the SEEPS triad and look for retrospinal fluid collections.
• 2.
  Conservative First-Line Management: Strict flat bed rest for 7–14 days, aggressive oral/IV hydration, high-dose oral Caffeine, and abdominal binder.
• 3.
  Non-Targeted Autologous Epidural Blood Patch (EBP): Administration of 15–25 mL of sterile autologous venous blood into the lumbar epidural space; provides rapid symptom relief in >70% of patients.
• 4.
  Dynamic Myelography for Refractory Cases: Dynamic CT Myelography or Digital Subtraction Myelography (DSM) to precisely localize high-flow dural tears or CSF-venous fistulas.
• 5.
  Targeted Intervention: Targeted CT-guided fibrin glue injection, transcatheter endovascular venous embolization (for CSF-venous fistulas), or microsurgical clip repair of mechanical dural tears.