Beyond the Surgical Margin: Patterns of Recurrence in World Health Organization Grade 2 Intracranial Meningiomas

OBJECTIVE: To characterize and classify the location of recurrence in surgically resected World Health Organization (WHO) grade 2 intracranial meningiomas that did not receive adjuvant radiation and compare the recurrence pattern of those who underwent gross total resection (GTR) versus subtotal resection (STR).METHODS: We performed a retrospective review of patients who underwent surgical resection of a newly diagnosed WHO grade 2 meningioma at our institution between 1996 and 2019. Patients who were observed postoperatively without adjuvant radiation and subsequently developed a recurrence were included in the study. All patients who received adjuvant therapy were excluded. Recurrence was defined as any evidence of radiographic progression on postoperative surveillance magnetic resonance imaging. Location of recurrence was categorized as follows: 1) central -growth observed inside the area of the previously resected tumor more than 1 cm inside the original tumor margin; 2) marginal -growth observed within 1 cm (inside or outside) of the original tumor margin; and 3) remote -growth observed >1 cm outside the original tumor margin. Patterns of recurrence were evaluated by 2 observers after coregistering preoperative and postoperative magnetic resonance imaging, and any differences were reconciled by discussion. RESULTS: A total of 22 patients matched the inclusion criteria. Twelve (55%) underwent GTR, and 10 (45%) underwent STR. In 12 patients in whom GTR was achieved, the mean preoperative tumor volume was 50.6 cm3, with 5 (41.7%) in a skull base location. The average time to recurrence for these tumors was 22.7 months, with a mean recurrent tumor volume of 9.0 cm3. Ten patients (83.3%) had central recurrence, 11 patients (91.7%) had marginal recurrence, and only 4 patients (33.3%) had remote recurrence. In 10 patients in whom STR was achieved, mean preoperative tumor volume was 44.8 cm3, with 7 (70.0%) in a skull base location. The average time to recurrence for these tumors was 23.0 months, with a mean recurrent tumor volume of 21.8 cm3. Of these 10 patients, 9 (90.0%) had central recurrence, all 10 (100.0%) had marginal recurrence, and only 4 (40.0%) patients had remote recurrence.CONCLUSIONS: The present study evaluating patterns of recurrence for WHO grade 2 meningiomas after surgical resection (GTR or STR) showed that recurrence occurred centrally and/or at the original tumor margin, with only a few recurring >1 cm outside the original tumor margin. The results of this study suggest that treatment, whether initial surgical resection or adjuvant radiation, may benefit from including at least a 1-cm dural margin when safe, to optimize tumor control, but further clinical study is needed.