COMPARISON OF METABOLIC AND RECEPTOR IMAGING IN RECURRENT MEDULLARY-THYROID CARCINOMA WITH HISTOPATHOLOGICAL FINDINGS

Early diagnosis of metastases of medullary thyroid carcinoma (MTC) pro vides the optimal condition for curative outcome. The aim of this stud y was to appraise the detection of metastases in patients with recurre nt MTC using [In-111-DTPA-D-Phe(1)]-pentetreotide and pentavalent tech netium-99m dimercaptosuccinic acid [Tc-99m(V)-DMSA] in comparison with histopathological findings. Eighteen MTC patients with persistently e levated tumour marker (calcitonin, carcinoembryonic antigen) levels un derwent somatostatin receptor scintigraphy using [In-111-DTPA-D-Phe(1) ]-pentetreotide (222 MBq) with early (4 h after injection) and delayed (24 h) whole-body scans and single-photon emission tomography (SPET) imaging, Metabolic whole-body and SPET imaging using 500 MBq Tc-99m(V) -DMSA was performed 4 h after injection. Metabolic and receptor imag i ng revealed 51 sites of focal accumulation in the 18 patients investig ated. Comparison with histological findings revealed that metabolic an d receptor imaging had a sensitivity of 84% for the diagnosis of MTC, Using [In-111-DTPA-D-Phe(1)]-pentetreotide, SPET discovered four lymph node metastases in two patients in whom planar views had previously i dentified only one lymph node metastasis, and provided no new informat ion in the other 16 patients. In comparison, SPET studies [using Intro duction 99mTc(V)-DMSA] additionally localized eight lymph node metasta ses in four patients and confirmed the diagnosis of hepatic metastases (n=5) in another patient in whom conventional imaging modalities and planar views had previously detected only three liver metastases, Over all, lesion detection sensitivities for Tc-99m(V)DMSA and [In-111-DTPA -D-Phe(1)]-pentetreotide were 69% and 29%, respectively. Five surgical ly removed foci were adjudged false-positive with respect to MTC metas tases, False-positve results were caused by lymphadenitis, an enchondr oma and a pheochromocytoma (histologically proven), The smallest lesio n identified by metabolic imaging was a 6 mm in diameter lymph node me tastasis located in the upper mediastinum. Somatostatin receptor scint igraphy only demonstrated tumour sizes more than 1 cm in diameter. The se preliminary results suggest that the combination of metabolic [Tc-9 9m(V)-DMSA] and receptor ([In-111-DTPA-D-Phe(1)]-pentetreotide) imagin g is more sensitive for tumour localization in patients with recurrent MTC than the use of only one radiopharmaceutical. However, neither 99 mTc(V)-DMSA nor [In-111-DTPA-D-Phe(1)]-pentetreotide is specific for M TC and false-positive scintigraphic findings have to be considered. Fu rthermore, somatostatin receptor scintigraphy cannot visualize small t umour sites (<1 cm). Further studies are needed to evaluate the role o f combined metabolic and receptor imaging in the management of patient s with recurrent MTC.