Spindle Cell Oncocytoma: Index Report of Outcomes after Stereotactic Radiosurgery and Systematic Review of the Literature

Introduction: Spindle cell oncocytoma (SCO) is a rare, nonadenomatous, sellar tumor, originally described in 2002 and first included within the WHO classification in 2007. Although designated benign (Grade I), late recurrences have been reported up to 13 years after treatment. With few cases reported, data are inconsistent or incomplete, and no results have yet been published regarding stereotactic radiosurgery (SRS) for SCO. We report the index experience with SRS for the treatment of 4 SCO, and review the pertinent literature.

Methods: Retrospective review of a prospectively maintained institutional SRS database and systematic literature review.

Results: We identified four patients who underwent SRS for SCO during the study period, 2002–2017. Median age was 61 (range: 54–79); three were male (75%). Prior treatments included transsphenoidal resection (TSR) alone in 2, multiple TSRs in 1, and TSR, radiotherapy, and craniotomy in 1; all operative treatments resulted in gross-total resection (GTR). Three patients were treated with SRS for recurrence after GTR (75%); 1 was treated adjuvantly following a third TSR (25%). Median target volume was 4,370 mm³ (range: 1,800–8,370), with a median margin dose of 16.5 Gy and a median maximum doses 33 Gy (range: 14–18 Gy; 28–36 Gy). Prior to SRS, 1 patient had incomplete pituitary dysfunction (25%), 3 were pan-hypopituitary (75%), and 2 had incomplete visual deficits (50%); no new endocrine, visual, or other neurologic deficits or radiation-induced complications were observed after SRS. The patient who had previously undergone multiple resections and radiotherapy subsequently failed SRS and required additional treatments; however, all radiation-naive patients achieved tumor control after SRS. No patient died of disease.

Systematic literature review identified 20 publications reporting 30 cases of SCO during the study period, 2002–2017. All 34 patients underwent initial resection, via TSR in 30 (88%) and craniotomy in 3 (9%); extent-of-resection for the preceding operation was GTR in 18 (53%), and STR in 15 (44%). Eleven instances of recurrence/progression (32%) were reported at a median 18 months (range: 5–132), 10 of which occurred after STR, a difference that was significant (p = 0.0008). Four recurrences presented with symptomatic hemorrhage of the tumor remnant (36%). Among previously reported patients, 6 underwent conventional fractionated radiotherapy (18%), 5 at the time of recurrence and 1 as an adjuvant after initial STR with significant postoperative residual in the cavernous sinus; the median dose was 54 Gy (range: 50–54).

Conclusion: SCO is a rare sellar neoplasm, our understanding of which is actively evolving. Recurrence is common, significantly associated with preceding STR, and may occur in a delayed fashion. Correspondingly, we recommend consideration for adjuvant SRS in patients with large or intracavernous residual. Further case accumulation is required to better characterize the natural history and long-term treatment outcomes; however, our initial results indicate potential for excellent tumor control with a minimal side effect profile after SRS for SCO.