Indium-111-pentetreotide imaging in intra-axial brain tumors: Comparison with thallium-201 SPECT and MRI

Highly undifferentiated glial tumors do not express somatostatin receptors (SSR) in contrast to low-grade astrocytomas which contain SSR. To differentiate a malignant glioma from a low-grade astrocytoma and to distinguish an SSR-positive intra-axial brain tumor from an SSR negative one, ¹¹¹In-pentetreotide brain SPECT was prospectively undertaken. Methods: Eight patients with intra-axial brain tumors (three glioblastoma multiforme, one low-grade astrocytoma, one lymphoma, one medulloblastoma, one neurocytoma and one metastatic tumor) were studied. Thallium-201 and ¹¹¹In- pentetreotide brain SPECT were performed with a 3- to 4-day interval before surgery. The SPECT findings were compared with those of Gd-enhanced MRI. Results: Increased uptake of ¹¹¹In-pentetreotide was observed in all of the patients with glioblastoma multiforme (Grade +++ in two and Grade + in one) despite lack of SSR. Low-grade astrocytoma exhibited minimal uptake of ¹¹¹In-pentetreotide (Grade +). Remaining tumors had intense uptake of ¹¹¹In-pentetreotide. Thallium-201 SPECT showed similar findings to those of ¹¹¹In-pentetreotide scintigraphy except in two patients with glioblastoma multiforme: One with ²⁰¹Tl negative scan showed increased uptake of ¹¹¹In-pentetreotide and the other showed increased thallium uptake but minimal uptake of ¹¹¹In-pentetreotide. The uptake pattern of both ²⁰¹Tl and ¹¹¹In-pentetreotide appeared to correlate with Gd- enhanced MRI. Conclusion: Indium-111-pentetreotide scintigraphy is sensitive in the detection of intra-axial brain tumors; however, it has no role in assessing the tumor grading and in the definition of the receptor profile.