Keywords
Gamma Knife radiosurgery - depressed skull fracture - cerebrospinal fluid rhinorrhea
Introduction
The genesis of Gamma Knife radiosurgery (GKRS) happened in early 1950s and Lars Leksell laid the initial foundations of stereotactic radiosurgery (SRS). Since then, numerous technological advancements have taken the field of SRS to new heights.[1] Stereotactic frame fixation is an integral step in radiosurgery that keeps the patient's head still in position to receive the precisely focused radiation. In this report, we describe an uncommon complication associated with stereotactic frame fixation that has so far not been reported in the literature.
Case Report
Our patient was a 75-year-old gentleman, a known case of right vestibular schwannoma, who had undergone right retrosigmoid craniotomy and decompression of tumor 2 years ago. GKRS was planned for the recurrent tumor measuring 2.8 × 2.1 × 1.8 cm ([Fig. 1A]).
Fig. 1 (A) Contrast MRI brain axial image showing a 2.8 x 2.1 x 1.8 cm recurrent right vestibular schwannoma. (B) CT brain plain bone window axial image showing left frontal sinus depressed fracture and underlying pneumocephalus with screw penetrating the inner table. (C) CT brain bone window axial and (D) CT brain plain sagittal images done post procedure shows evolution of the pneumocephalus. 3-months Post treatment contrast MRI brain (E) sagittal and (F) axial images showing complete resolution of pneumocephalus and radiation necrosis within the tumor.
At frame fixation, the right posterior pole of the frame was positioned at a higher level to avoid penetration of the screw into the previous craniotomy bony defect. During frame fixation, the left anterior screw penetrated the skull, which was noticed immediately due to the giveaway sensation during screw tightening. The suspicion was confirmed on computed tomography (CT) brain, which revealed a depressed skull fracture of the left frontal bone with an underlying left frontal region pneumocephalus ([Fig. 1B]). The GKRS procedure was completed and the prescribed radiation dosage of 13 Gy at 50% isodose was delivered on the defined target. After removal of the frame, the skin was stitched with Ethilon 3–0 suture.
The postprocedure CT brain revealed evolution of pneumocephalus, compressing the bilateral frontal lobes ([Fig. 1C] and [D]). On the next day, the patient had cerebrospinal fluid (CSF) leak from the left nostril. Conservative treatment was started in the form of bed rest, acetazolamide, and high-flow oxygen. However, CSF leak from the left nostril persisted. Hence, on the third day of GKRS, he was taken up for operation. A left frontal craniotomy was performed and the dural defect was repaired using a pericranial graft augmented with fat, muscle, and fibrin glue. At 3 months of follow-up, the patient had no CSF rhinorrhea and a follow-up magnetic resonance imaging (MRI) scan of the brain showed complete resolution of pneumocephalus and the expected radiation necrosis within the tumor ([Fig. 1E] and [F]).
Discussion
GKRS offers a minimally invasive and a relatively safe alternative to conventional microsurgery for intracranial lesions. Complications can be broadly categorized into complications due to radiation and complications related to frame fixation. Rarely, acute problems from radiosurgery can arise from radiation-induced edema, which can produce convulsions and new neurological deficits.[2]
The pin headrest–related complications reported thus far include penetration into the skull, epidural hematoma, scalp laceration, and tension pneumocephalus.[3] These are generally attributed more to the Mayfield clamp fixation and are more commonly seen in the pediatric age group.[3] There have been reports of stereotactic frame penetration of the large frontal sinus causing penetration of the outer cortex, but depressed skull fracture resulting in pneumocephalus and CSF rhinorrhea has not been reported.[4]
Thinner areas that are more likely to give away, like the frontal sinus, squamous part of temporal bone, and the coronal suture, should be avoided in pin fixation.[3] One must also be mindful of the craniotomy defects of previous surgeries. Systemic causes like metastatic tumors, hyperparathyroidism, granulomatous diseases, osteomyelitis, and bony anomalies such as bone aneurysm, and cystic angiomatosis can also cause thinning of the bony cortex.[5] Finally, the technique of frame fixation must always be kept in mind as excessive pressure application while fixing the screws can also be an extremely critical factor.[3] The pins should be tightened on the diagonal with thumb and index finger grip to limit the torque applied.[6]
GKRS has many subtleties and being a day care procedure, these are often overlooked. On retrospection, it was proposed that the anatomically large frontal sinus and age-related osteoporotic thinning of the skull were the factors that predisposed to depressed skull fracture in our patient. We aim to shed light on one such rare complication of GKRS frame fixation so that the neurosurgeons can better prepare, be more alert, and prevent the iatrogenic depressed skull fracture and its sequela.
Conclusion
The occurrence of iatrogenic skull fracture and CSF rhinorrhea after GKRS frame fixation is rare. The special anatomical features such as abnormally thin skull, large frontal sinus, and anatomical thinning of the squamous temporal bone and coronal sutures should be taken into consideration in every patient subjected to GKRS frame fixation.
