This case demonstrates the rare occurrences of:
- post-dural puncture headache, intracranial hypotension and cranial acute subdural hematoma, all likely resulting from the lumbar puncture procedure performed during myelography
- brainstem intraparenchymal hemorrhage secondary to evacuation of acute subdural hematoma
The Monro–Kellie doctrine states that the human skull is a rigid box with three major compartments: brain, cerebrospinal fluid (CSF), and blood. In order to keep the intracranial pressure constant, the volume loss of one is compensated by an increase of the volume of the other compartments1,2. Most cases of intracranial hypotension result from a persistent CSF leak3. This CSF leak may occur spontaneously (Spontaneous Intracranial Hypotension) or following dural puncture for a diagnostic LP, myelography, spinal anaethesia, accidental intraoperative dural opening and/or excessive surgical cerebrospinal fluid drainage3. Whichever the cause, it leads to alterations in the equilibrium between the volumes of intracranial blood, CSF, and brain tissue. If CSF is lost slowly, compensation mainly occurs through increase of the cerebral blood volume, especially of the venous blood, because veins are inherently less resistive to expansion than arteries. If CSF is lost rapidly, the brain tissue is displaced and damaged leading to serious clinical consequences.
The typical clinical manifestation of intracranial hypotension is an orthostatic headache1,2. This headache is thought to be caused by a decrease in intracranial pressure from continuing leakage (of up to 240 ml per day) of CSF into the epidural space through the hole caused by puncture of the meninges1-7. Volume depletion is partially compensated for by dilatation of cerebral veins, leading to an increase in brain volume. The loss of CSF volume induces caudal displacement of intracranial structures and traction of both pain-sensitive receptors and small subdural bridging veins. Whenever the patient changes from a recumbent to an upright position, traction and stretching increase, due to gravity, manifesting as a headache.
- Other less common presentations include2,5:
- cranial nerve palsies
- coma (due to caudal displacement of the brain parenchyma following rapid CSF loss)
- Cortical vein and sinus thrombosis
- Unilateral hearing loss (postulated to result from perilymph depression in patent cochlear aqueduct. This induces a compensatory expansion of the endolymphatic compartment with a subsequent decrease in basilar or Reissner’s membrane compliance)6
Typical radiographic findings of intracranial hypotension on:
1. CT brain imaging include2,3:
a. obliteration of the basilar cisterns due to sagging of the brain
b. subdural hemorrhage
c. cerebellar tonsillar herniation into the foramen magnum (acquired Chiari I malformation)
d. dural venous sinus distention
e. dural thickening
2. MRI brain include2,3:
a. Diffuse brain swelling and sagging of the brain with downward displacement of the tonsils
b. pachymeningeal enhancement
c. engorgement of venous structures
d. enlargement of the pituitary gland
e. subdural effusions
Treatment of Intracranial hyptotension involves conservative measures (such as bed rest and oral hydration), or prevention of CSF egress/leaks via epidural blood patch/fibrin patch or surgery.
As illustrated by this case, this patient’s recovery was drastically hindered by the post-procedure complication of a subdural hematoma. This rare, but potentially life-threatening, complication has been reported both after lumbar myelography and following lumbar puncture for spinal anaesthesia7. The primary mechanism for cranial SDH can be explained by the resultant intracranial hypotension, which allows caudal shift of the brain. There is subsequent traction on the arachnoid mater and dural veins, which causes tears in the blood vessels. Blood extravasation ensues, with the formation of a subdural hematoma8.
Despite urgent evacuation of the acute subdural hemorrhage, the patient failed to make any significant functional post-operative gains with imaging revealing a catastrophic brainstem hemorrhage. Post-operative complications, though rare, following evacuation of subdural hematomas, include: re‑accumulation, re‑hemorrhage, cerebral edema, infection, seizures, and intracerebral hemorrhage (ICH)9. ICH is a well‑known complication of supratentorial neurosurgery, however, ICH following evacuation of a subdural hematoma is a rare clinical event 10. The post-operative ICH may occur on the ipsilateral or contralateral side of the evacuation, infratentorially and extremely rarely cerebellar or, as in this case, within the brain stem9. The pathogenesis of postoperative hemorrhage after SDH evacuation is not well understood. Postulated mechanisms include increases in cerebral blood flow, alteration in vascular autoregulation, damage of small fragile vessel, secondary to increased intracranial pressure or damage directly to a vessel following transtentorial herniation9,10. With specific reference to post-operative brainstem hemorrhages, it is thought that a hypertensive crisis (with or without raised intracranial pressure) is responsible for the formation of a brain stem hematomas, and therefore, unrelated to surgical manipulation9.
Case courtesy of Associate Professor Pramit Phal