99MTC-MIBI use as a non-specific tumour marker in the diagnosis of brain metastases of unknown primary malignant etiology

Tumours of unknown etiology are a heterogeneous group of malignancies whose first presentation is a metastatic disease and the primary neoplasm site remains not detected by the time of initial diagnosis. Brain is a relatively common localization for metastases from various malignancies, mainly from lung, melanoma, kidney, etc. In certain cases, however, the primary tumour site could not be diagnosed by routine tests and additional methods are utilized in attempt to localize it. We aimed at evaluating the use of 99mTc-MIBI as a non-specific tumour marker in patients with brain metastases and unknown primary tumour site. The study covered 11 patients with brain metastases but without any evidence of primary tumour according to the routine diagnostic tests. A single i.v. dose of 20 mCi 99mTc-MIBI was used as a non-specific tumour marker. All the patients underwent the following examinations: dynamic perfusion study of the abdomen, scintimammography (females), SPECT of thorax, whole body scan, and brain SPECT performed consecutively by means of Diacam Siemens gamma camera. Two patients showed a pathologic MIBI uptake in the lung morphologically proven to be non-small cell lung cancer (NSCLC). Lesions were evident on SPECT only. One patient demonstrated MIBI uptake in the axillary lymph nodes, however, no primary tumour site was verified thereafter. The remaining 8 patients did not show any foci of abnormal MIBI uptake consistent with the primary tumour or extracranial metastases. Usage of 99mTc-MIBI as a non-specific tumour marker could be of value for detecting the primary tumour site in case of brain metastases of unknown etiology.Scripta Scientifica Medica 2012; 44(2): 41-44