Burr Hole

close up of burr hole craniotomy procedure performed by Dr. osborn


“Burr holes” are typically placed to access the subdural space and drain (evacuate) subacute or chronic blood that is pressing on the brain. This procedure is not performed to address an acute subdural hematoma as acute blood is too viscous and not amenable to removal through small holes.

  • This procedure is usually performed under IV sedation with local anesthesia.
  • The correct side of the head is identified and shaved.  Incisions are marked over the largest part of the hematoma (as visualized on the preoperative CT scan).
  • The head is then prepped, draped and the previously marked incisions are made.
  • Burr holes (typically two) are made in the skull with a “perforator.” This drill has an automatic stop mechanism that prevents the surgeon from violating the dura (leathery outer membrane which covers the brain).
  • The dura is then opened with a blade, allowing for egress of blood product (chronic and subacute) from the subdural space. Often, the blood shoots out of the burr hole(s) under pressure. Reiterating, this operation is geared towards alleviating pressure on the brain.
  • Dr. Osborn then irrigates the subdural space (on top of the brain, not in the brain) with antibiotic-impregnated saline solution. Essentially, the irrigation is performed from burr hole to burr hole (the volume of fluid entering one hole exits the other).
  • After irrigation proves clear (the blood product having been irrigated out), a small drainage catheter is inserted into the subdural space (essentially placed carefully on the surface of the brain). The drain exits the skin from a separate small incision.
  • The incisions are closed and the subdural catheter is affixed to a closed drainage system. It typically remains in place for 48-72 hours. Timing of its removal is based on CT scan findings.


“I fell 6 weeks ago. Why do I still have bleeding on the brain?”

Good question. At the time of the fall, there was likely a small amount of blood introduced into the subdural space (a small “bridging vein” was torn). This did not become clinically apparent (aside from a headache) because the bleeding stopped immediately. However, the mere presence of the blood in the subdural space catalyzed an inflammatory response (the details of which are being worked out in laboratories) and resultant fluid (likely not new blood) accumulation on the brain’s surface. This is the same inflammatory response that occurs elsewhere in the body in response to a foreign substance (yes, blood in the subdural space is interpreted as foreign to the body).  In this regard, high-dose steroids are sometimes used to treat subdural hematomas (as they are potent anti-inflammatories).  

“How long does this type of surgery take?”

A typical burr hole procedure takes approximately 30-45 minutes depending on complexity. There is a small (< 2%) chance that one may require a more extensive procedure (formal craniotomy) in the event of unexpected intraoperative bleeding.

“My father had a subdural hematoma and needed a big operation. The surgeon made a big cut.”

One of two things occurred. Either your father was seen in the wake of a trauma and had acute bleeding on the bleeding or he had a smaller operation first, but the hematoma recurred and warranted a larger “second-look” operation. Let me explain.

Acute subdural hematomas are typically treated with a formal craniotomy because the blood is simply to thick to be evacuated through nickel-sized holes.  More simply put, a larger opening in the bone is (was) required.  


Your father may have had burr holes for a chronic subdural hematoma but the fluid was incompletely evacuated due to presence of “loculations,” compartmentalized pockets of fluid within “subdural membranes,” a byproduct of the inflammatory response. The membranes, often spanning a large area are best accessed and fenestrated (opened) through a craniotomy. Any bleeding from the membranes (as they are vascular) is addressed at this point. Such second-look operations typically resolve the issue.

“What are some of the potential surgical complications?”
  • Seizures. Patients are uniformly placed on prophylactic anticonvulsants in this regard (the blood product in the subdural space is an irritant and may cause seizures).
  • Failure of the brain to re-expand and/or reaccumulation of the subdural fluid necessitating repeat drainage procedures.
  • Wound infection.
  • Subdural empyema. This infection within the subdural space itself can be life-threatening and typically warrants an emergency craniotomy (during which pus is evacuated from the brain surface).
“For how long will I be laid up after surgery? When can I return to my normal activities?”

Burr hole procedures are typically well tolerated, and patients are aggressively mobilized postoperatively.  Inpatient rehabilitation may be required should you have neurologic deficits (i.e., weakness or sensory loss on one side of the body).  You may return to normal activities 6 weeks postoperatively barring any interval neurologic changes or preclusive CT scan findings (recurrent/expanding subdural fluid collection).

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