Spontaneous Decompression of an Enlarging Cyst following Gamma Knife Radiosurgery for a Vestibular Schwannoma

Objective: Our goal is to present a clinical case vignette of an enlarging postradiation acoustic neuroma tumoral cyst that progressed over a 10-year period, but ultimately decompressed spontaneously without the need of surgical intervention.

Presentation: A 54-year-old female patient presented with a recurrent left-sided cystic acoustic neuroma. She was initially diagnosed in 1999 following routine image evaluation for a motor vehicle accident, and subsequently had a subtotal resection via a translabyrinthine approach at an outside institution. On initial consultation, she was noted to have left ear deafness, reduced sensation in her left V2 and V3 distributions, left-sided synkinesis with hemifacial spasm, and House-Brackmann grade III/VI left facial weakness.

Intervention: In April 2004, the patient underwent Gamma Knife radiosurgery (GKRS) for her recurrent tumor. The dose planning consisted of one 14-mm isocenter and ten 8-mm isocenters which covered 6.2 cm³. The dose to the margin was 13 Gy and the maximal dose was 26 Gy. The procedure was well tolerated and resulted in no adverse symptoms or side-effects. The patient was subsequently followed with yearly serial MRI evaluations. The solid portion of her tumor involuted and shrank significantly over time. However, 2 years following GKRS the patient developed a cyst from the medial aspect of the tumor wall. On subsequent scans, the cyst became progressive larger resulting in brain stem compression. However, the patient was asymptomatic from this, and was reluctant to undergo further intracranial surgery. On her most recent follow-up, the patient was noted to have a spontaneous decompression of her tumor cyst, thus eliminating the need for surgical intervention.

Conclusion: The development of tumoral cysts following gamma knife radiation has been observed in the literature, especially with larger acoustic neuromas, but why or how these cysts develop is poorly understood. It is not currently known if the development of cysts following gamma knife radiation is a risk factor for poor prognostic outcome. However, this case illustrates that an instance in which an asymptomatic cyst improved with observation alone.