Clinical significance of solitary focal uptake in the sacrum on Tc-99m HDP bone scintigraphy

Objectives The interpretation of a single focal uptake on bone scan of a cancer patient is often difficult due to the nonspecific nature of the exam. The objective of this study was to evaluate the clinical significance of a single focal uptake in the sacrum.

Methods Tc-99m HDP bone scans from July 2010 to June 2012 were retrospectively reviewed. Inclusion criteria were the visualization of a single focal uptake in the sacrum and availability of a minimum 6 months follow up with serial bone scan or other imaging modalities such as computed tomography, magnetic resonance imaging and PET/CT. The lesions were analyzed with respect to location and intensity of uptake. The location were categorized as ala, mid body and lower body. Intensity was divided into 3 groups by visual grading, with 1 being the faintest, and 3 the strongest.

Results 37 patients (10 men and 27 women, mean age 60±13) were included in this study. 25 patients demonstrated uptake in the ala, and 3 of whom were confirmed as bone metastasis. 4 were in mid body with no bone metastasis. Eight were in lower body, with one case of bone metastasis. 4 uptakes were grade 1, of which none were metastatic. 1/ 19 grade 2, and 3/14 grade 3 were bone metastases. Bone metastasis was confirmed in patients with HCC, bladder, prostate and stomach cancer. Of 33 cases which were confirmed as benign lesions, 6 were found to be sacroilitis, 4 had bone islands, 5 were fractures, and 1 was intraosseous lipoma. 6 showed no bone abnormality in other imaging modalities images, and 11 had had no other studies done, but remained unchanged or resolved uptake in serial bone scans.

Conclusions Most solitary focal uptakes of the sacrum on bone scan of cancer patients are benign, especially if the uptake is subtle. However, in patients with intense focal uptake, the possibility of bone metastasis should be considered as a differential diagnosis.