Gamma Knife radiosurgery in skull base meningiomas: a possible relationship between somatostatin receptor decrease and early neurological improvement without tumor shrinkage at short-term imaging follow-up

Abstract

BACKGROUND: This study investigates a possible relationship between the effects of gamma knife (GK) on meningioma somatostatin receptors (SRs) and the high rate of early neurological improvement without tumour reduction at short-term imaging follow-up. METHODS: From December 1997 to December 2002, somatostatin receptor scintigraphy (SRS) using an 111Indium-labelled somatostatin analogue, Octreotide, was performed both before and 7-12 months after radiosurgery in 20 patients with intracranial meningiomas. Semiquantitative data were calculated as an SRS index. FINDINGS: The pre-GK SRS index was always > 1, averaging 4.44 +/- 3.20. There were no statistically significant differences between the pre-GK average values of primary (4.80 +/- 3.65) and residual (3.75 +/- 1.93) meningiomas. At the first clinical/MRI follow-up, the neurological examination had improved in 15/20 (75%) and had not changed in 5/20 patients. A corresponding slight tumour shrinkage on high-resolution MRI was documented in 3/20 cases only. The post-GK average SRS index was lower than pre-GK values both in primary (3.87 +/- 3.19) and in adjuvant (2.52 +/- 1.14) treatments, but the differences were not significant. However, the subgroup of patients with early neurological improvement showed a higher pre-GK average SRS index (5.21 +/- 3.33) and a more substantial post-GK average SRS index decrease (3.86 +/- 3.00) than the patients whose clinical condition remained stable (2.10 +/- 0.59 and 1.99 +/- 0.55, respectively). The difference between the two subgroups of patients proved to be statistically significant (P < 0.05). CONCLUSIONS: Our preliminary findings suggest a possible relationship between a decrease in the concentration of SRs on meningioma cells at short-term functional imaging follow-up after radiosurgery and early neurological improvement