Simpson Grade Revisited - Intraoperative Estimation of the Extent of Resection in Meningiomas Versus Postoperative Somatostatin Receptor Positron Emission Tomography/Computed Tomography and Magnetic Resonance Imaging.

BACKGROUND: Surgeon's intraoperative estimation of meningioma extent of resection (Simpson Grade, SG) is widely used as a prognostic factor for recurrence. However, the validity of SG is still a matter of debate. In preoperative imaging, 68Ga-DOTATATE/PET-CT has been shown to detect meningioma tissue even more sensitively than magnetic resonance imaging (MRI). OBJECTIVE: To evaluate the Simpson grading within the framework of modern postoperative imaging techniques (MRI; PET-CT). METHODS: At first, patients with WHO grade I meningioma, surgical resection, and postoperative 68Ga-DOTATATE/PET-CT within 6 mo after surgery were retrospectively analyzed. Second, an analogous prospective cohort of patients with WHO grade I meningioma was investigated by comparing SG after meningioma removal with postoperative MRI and 68Ga-DOTATATE/PET-CT within 6 mo after surgery. RESULTS: A total of 37 patients were retrospectively analyzed. In total, 5/8 patients with SG-I and II resections showed tumor remnants according to postoperative PET-CT (SG 62.5% false negative). In the prospective cohort of 52 tumors, PET-CT displayed tracer uptake in 15/37 SG-I or II resections indicating unexpected tumor remnants (SG 40.5% false negative). MRI was false negative in 7 of these 15 cases (MRI 18.9% false negative) (P = .037). Discordant results according to PET-CT were more often found in convexity (40%) and falcine (46.7%) meningiomas than in skull base meningiomas (18.2%). CONCLUSION: Intraoperative Simpson grading is at risk to underestimate tumor remnants, predominantly in grade I and II resections. Postoperative PET-CT improves detection rates compared to MRI. Prognostic impact of postoperative meningioma remnants according to PET-CT needs to be investigated prospectively.

68Ga-DOTATOC PET/CT Differentiates Meningioma From Dural Metastases.

A 77-year-old woman with history of breast cancer presented with 2 unclear dural contrast-enhancing lesions on MRI; differential diagnoses were breast cancer metastases and meningiomas. On Ga-DOTATOC PET/CT, the temporal lesion showed high uptake and was classified as meningioma, whereas the lesion at the falx showed barely any Ga-DOTATOC uptake uncharacteristic for meningioma and suggestive for a brain metastasis. After resection, histological specimens from the temporal lesion showed meningioma tissue with distinct SSTR2A expression, whereas the falx lesion revealed a breast cancer metastasis without significant SSTR2A expression. Therefore, Ga-DOTATOC PET represents a powerful imaging modality for the evaluation of unclear dural lesions.

Neurosarcoidosis Mimics High-Grade Glioma in Dynamic 18F-FET PET Due to LAT Expression.

We present a 45-year-old man with newly generalized tonic-clonic seizures due to a contrast-enhancing frontal lesion with perifocal edema suggestive for high-grade glioma (HGG). For further evaluation, a dynamic F-FET PET scan was performed, which showed high F-FET-uptake with early peak and constantly decreasing time-activity curves, a characteristic feature of HGG. Stereotactic biopsy and histological evaluation excluded a neoplastic lesion but confirmed a manifestation of neurosarcoidosis with strong expression of the L-amino-acid-transporter considered responsible for F-FET-uptake. Therefore, unknown manifestations of neurosarcoidosis represent a clinical pitfall in F-FET PET and can mimic HGG.