Bone Regrowth After Frontal Burr Hole Craniostomy: Natural History of 14-mm and 20-mm Burr Holes and Implications for Postoperative Trans-Burr Hole Ultrasound

BACKGROUND AND OBJECTIVE: Burr hole craniostomy is performed for ventriculoperitoneal shunt insertion and endoscopic third ventriculostomy in patients with cerebrospinal fluid disorders. These burr holes are increasingly being used as windows for postoperative ultrasound, an investigational alternative to computed tomography or MRI for follow-up imaging of ventricular caliber. However, bone regrowth reduces ultrasound visibility, and little is known about burr hole regrowth rates in adults. Our study evaluates burr hole regrowth patterns and implications for transcranial ultrasound imaging. METHODS: We retrospectively analyzed 101 consecutive patients who had frontal burr hole craniostomy for new ventriculoperitoneal shunt insertion or endoscopic third ventriculostomy over a 3-year period. A mix of standard 14-mm burr holes and expanded 20-mm burr holes were used. Burr hole bone regrowth was assessed using serial follow-up computed tomography scans. Linear and logistic regression analyses examined if bone regrowth correlated with any clinical variables. RESULTS: There was wide variability in rate and degree of burr hole regrowth. The average percentage closure was 25% at 6 months, with minimal additional closure over the following 18 months. The mean residual diameter for 14-mm and 20-mm burr holes stabilized around 9.4 mm and 15.4 mm, respectively. Bone regrowth was not associated with patient characteristics, including age, sex, skull thickness, or etiology of cerebrospinal fluid disorder. Rate of bone regrowth was similar between both cohorts. CONCLUSION: Bone regrowth after burr hole craniostomy is common, even in elderly patients, occurring rapidly within the first 6 to 12 months and subsequently stabilizing. It is frequently severe enough to restrict ultrasound visualization. Regrowth could not be predicted with any investigated variables, so uniform techniques are needed to block regrowth to allow for longitudinal ultrasound imaging, such as full-thickness cylindrical burr hole implants.