What is a dime-sized opening in the skull to access the brain called, is it a burr hole, (b) trephine, (c) cistern, or (d) craniectomy?

Dime-Sized Opening in the Skull for Brain Access

A dime-sized opening in the skull to access the brain is called a burr hole. 1, 2

Definition and Clinical Context

A burr hole is a small circular opening (approximately dime-sized) drilled through the skull to access the brain for various neurosurgical procedures. This technique represents one of the oldest and most fundamental neurosurgical procedures, dating back to ancient civilizations 3.

Key characteristics of burr holes include:

• Typically 14mm in diameter (approximately dime-sized) 4
• Created using specialized drilling equipment
• Provides minimally invasive access to intracranial structures
• Often serves as the initial step in more complex cranial procedures

Clinical Applications of Burr Holes

Burr holes are utilized in numerous neurosurgical scenarios:

1. Emergency Management:

   • Evacuation of epidural or subdural hematomas 1
   • Relief of increased intracranial pressure in acute settings 5
   • External ventricular drain (EVD) placement for hydrocephalus 2

2. Diagnostic Procedures:

   • Brain tissue biopsy 1
   • CSF sampling
   • Endoscopic visualization of intracranial structures 1

3. Therapeutic Interventions:

   • Chronic subdural hematoma drainage 6
   • Ventriculoperitoneal shunt placement 2
   • Endoscopic third ventriculostomy for hydrocephalus 1, 2
   • Selective microsurgical approaches for tumors 4

Differentiation from Other Skull Openings

It's important to distinguish burr holes from other types of skull openings:

• Trephine: Historically refers to a circular piece of skull removed using a specialized saw (trephine). In modern usage, sometimes used interchangeably with burr hole but typically refers to a slightly larger opening 3

• Cistern: Not a skull opening but rather a CSF-filled space within the brain's subarachnoid area 1

• Craniectomy: Surgical removal of a portion of the skull without replacement, creating a much larger opening than a burr hole 1

Clinical Significance and Outcomes

Burr hole procedures offer several advantages in neurosurgical practice:

• Reduced Morbidity: Less invasive than traditional craniotomy with potentially lower complication rates 4
• Faster Recovery: 97.5% of patients undergoing burr hole microsurgery were mobilized within the first 3 postoperative days 4
• Versatility: Can be used for multiple approaches (transcortical, retrosigmoid, subtemporal, etc.) 4
• Emergency Application: Can be life-saving in time-critical scenarios such as expanding epidural hematomas 5

Potential Complications

While generally considered safe, burr hole procedures carry some risks:

• Remote hemorrhage from overdrainage of CSF 6
• Infection
• Cortical injury
• Cosmetic concerns from skull defect (addressable with various plug materials) 7

Burr hole covers made of hydroxyapatite have shown better aesthetic and biomechanical outcomes compared to autologous bone dust when addressing the cosmetic defect 7.

Modern Innovations

Recent advances have expanded the utility of burr hole approaches:

• Microsurgical techniques through 14mm burr holes have achieved gross total or near-total tumor removal in 87% of cases in one series 4
• Endoscopic assistance allows for improved visualization and more complex procedures through these small openings 1

In summary, burr holes represent a fundamental neurosurgical technique that continues to evolve, offering minimally invasive access to the brain for both emergency and elective procedures.