A lumbar cerebrospinal fluid drain is requested to improve surgical exposure during excision of a large posterior fossa tumour. Preoperative imaging shows significant obstructive hydrocephalus. Why should this request be refused?

• A Lumbar drainage causes refractory hypotension from sympathetic blockade
• B Lumbar drainage abolishes somatosensory evoked potentials
• C Lumbar drainage causes rapid reaccumulation of the tumour cyst
• D Lumbar drainage precipitates upward herniation of the cerebellar tonsils ✓

Explanation

In a posterior fossa mass lesion with obstructive hydrocephalus, the supratentorial and infratentorial compartments are pressure separated. Draining CSF from the lumbar subarachnoid space lowers spinal axis pressure while the posterior fossa pressure remains high, creating a gradient that can cause upward transtentorial herniation of the cerebellar tonsils. Lumbar drains are acceptable after the dura is opened or when there is free communication between compartments, but not before decompression in this setting.

Reference: Miller's Anesthesia, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.