= rare cause of orthostatic headache worsening in upright position

Cause:

1. persistent CSF leak:
   diagnostic lumbar puncture, spinal anesthesia, myelography, craniotomy, spinal surgery, trauma
2. spontaneously:
   rupture of Tarlov cyst, dehydration, hyperpnea, uremia, diabetic coma

• low CSF opening pressure of <80 mm H₂O
• sagging of posterior fossa:
  • low-lying cerebellar tonsils
  • elongation of 4^th ventricle
  • effacement of prepontine cistern
• diffuse smooth linear pachymeningeal enhancement ←↑ intracranial venous blood flow compensating for CSF loss
• bilateral subdural effusions
• enlarged pituitary gland

Rx: conservative therapy with bed rest; autologous epidural blood patch