ATYPICALLY LOCATED SINGLE HOT SPOT IN BONE SCINTIGRAPHY: HOW OFTEN IS IT A METASTASIS?

Abstract

OBJECTIVES: 1) To identify the frequency of bone metastases which appears as atypically located single hot spot on bone scan in patients with extraosseous malignancy but without current evidence of metastatic bone diseases. 2) To identify the common sites of metastasis with such findings.

MATERIALS AND METHODS: All bone scans of the patients with extraosseous malignancy but without current evidence of metastatic bone diseases performed at Ramathibodi Hospital during January 1996 to December 1997 were selected. A nuclear medicine physician blindly reviewed the selected scans and only the scans with atypically located single hot spot were included for clarification of their causes. The verification procedure includes histology, CT, MRI, progression of bone scan lesions, or a clinical follow-up of at least 2 years.

RESULTS: During the specified period, there were 100 patients (62 women, 38 men; age range 25-81 years; mean age 57.96 years) with atypically located single hot spot without known skeletal metastasis. Bone metastasis was confirmed in 8 patients (8%); 4 with breast cancer, 2 with cervical carcinoma, and 2 with head and neck cancer. Such findings were classified as benign lesions in 64 patients and as indeterminate in 28 patients. The frequency of a hot spot being a metastatic focus is 2 of 7 (28.57%) at the sternum, | of 28 (3.57%) at the ribs, 1 of 4 (25%) at the costovertebral junction, and 4 of 41 (9.76%) at the lower lumbar spine. None of such findings were proved to be malignant at the cervical spine, the scapula, the manubrium, the sacrum and the sacroiliac joint.

CONCLUSION: The frequency of bone metastasis which appears as atypically located single hot spot on bone scan in patients with extraosseous malignancy but without current evidence of metastatic bone disease was 8%. The most common site of such findings is the sternum, particularly in patients with breast cancer.