Thallium scintigraphy used in the evaluation of soft tissue sarcoma

Full text: The use of thallium scintigraphy in tumour localisation is a promising diagnostic modality. Thallium has a good affinity for numerous tumour types including sarcomas. Its properties as a potassium analogue result in active uptake via the sodium- potassium ATP-ase pump enabling its use in evaluating tumour extent, viability, staging, localisation and treatment. This case illustrates the role of thallium in tumour staging. A 67-year-old woman with a fibrous histiocytoma resected from the right foot four months previously presented with pain in the ribs, lower back and feet. A bone scan was performed to assess the possibility of metastatic disease. Several abnormal foci were seen on the bone scan suggestive of metastatic disease. A thallium scan was performed to confirm the bone scan result after a subsequent CT scan showed no evidence of this extensive disease. Static images of the whole body were acquired on an Elscinct 400AG 20 minutes post i.v. injection of 3.5 mCi of thallium. Focal areas of increased thallium uptake were seen in the 11th rib posteriorly and in the left sacroiliac region corresponding with sites on the bone scan suggesting metastases. However, an extensive area of uptake was also observed in the right inguinal region which had no corresponding abnormalities in the bone study. This was thought to be tumour metastasis in an inguinal Iymph node, which was retrospectively confirmed on an earlier CT scan of the pelvis. This study demonstrates the usefulness of thallium in the detection of soft tissue tumours and metastases. Thallium also exhibits potential in the assessment of tumour extent and viability pre- and post-treatment. This potential needs to be explored further in patient management