Focal small-bowel localization of bone-imaging radiopharmaceutical in a child.

Bone scintigraphy is an important diagnostic tool in the evaluation of skeletal pathologic conditions. However, the extraskeletal uptake of bone-seeking radiotracers is still an unexpected finding in most cases. We present a 5-year-old male with an unexpected focal accumulation of the radiotracer in the small bowel. Bowel accumulation of bone-seeking radiopharmaceuticals has been seen previously in children in the colon and mainly in the cecum, but not in the small bowel. The mechanism for such accumulation is not completely clear and may be explained by focal histological disturbances of a small-bowel segment that contributed to excretion of the radiotracer from the blood-to-bowel lumen.

Case report

A 5-year-old male, previously healthy, was referred for radiography of the spine due to low back pain. The radiograph revealed sclerosis and thickened trabeculae of the vertebral body S1, pathognomonic for hemangioma (Fig. 1), but no findings explained the lower-back pain. The patient was referred for bone scintigraphy, which revealed no abnormal uptake of the Tc-99m-methylene diphosphonate in S1 (Tc-99m-MDP), as demonstrated in the delayed SPECT/CT (Fig. 2).

Figure 1

5-year-old male with focal accumulation of radiotracer in the small bowel. Lateral radiograph of the lumbo-sacral spine reveals sclerosis and thickened trabeculae of the vertebral body S1, pathognomonic for hemangioma.

Figure 2

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed lateral view of SPECT/CT revealed no abnormal uptake of the bone-seeking radiopharmaceutical in the vertebral body S1.

3-D delayed bone scintigraphy of the patient revealed extra-osseous uptake of the radiotracer (99m-Tc-MDP) in the pelvis (Fig. 3). Axial (Figure 4, Figure 5), coronal (Figure 6, Figure 7), and sagittal (Figure 8, Figure 9) views of SPECT/CT revealed the focal extra-osseous uptake of the radiotracer in the small bowel.

Figure 3

5-year-old male with focal accumulation of radiotracer in the small bowel. 3-D delayed bone scintigraphy revealed extra-osseous uptake of the radiotracer (99m-Tc-MDP) in the pelvis.

Figure 4

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed pelvic axial view of SPECT/CT revealed focal extra-osseous uptake of the radiotracer in the small bowel.

Figure 5

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed pelvic axial view of the SPECT/CT, the same as Figure 4 without the SPECT component.

Figure 6

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed pelvic coronal view of SPECT/CT revealed focal extra-osseous uptake of the radiotracer in the small bowel.

Figure 7

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed pelvic coronal view of the SPECT/CT, the same as Figure 6 without the SPECTs component.

Figure 8

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed pelvic sagittal view of SPECT/CT revealed focal extra-osseous uptake of the radiotracer in the small bowel.

Figure 9

5-year-old male with focal accumulation of radiotracer in the small bowel. Delayed pelvic sagittal view of the SPECT/CT, the same as Figure 8 without the SPECT component.

Discussion

99m-Tc-MDP can be observed in the intestines in 1% of bone scans with a prominent localization in the ascending colon; rarely, it appears all over the intestines (1). Intense bowel accumulation of bone-seeking agents can be seen in cases of occult gastric bleeding (2), intestinal infarction (3), enterovesical fistula (4), urinary diversion surgical procedure (5), protein-losing enteropathy (6), primary intestinal lymphangiectasia (7), systemic AL amyloidosis (8), and uptake in normal intestine in children. In children, the radiotracer accumulated in the cecum is presumably secondary to concentration via water absorption. Factors that probably enhance this localization are rapid bowel motility, delayed imaging times, improved resolution of imaging systems, an awareness of its appearance, and unknown factors that may be related to the radiopharmaceutical (9).

Our images demonstrate focal accumulation of the radiotracer in the small bowel. The CT images that were obtained as part of the SPECT/CT are of low resolution. Our patient subsequently underwent a CT with oral and intravenous contrast, which was completely normal without any bowel or soft-tissue pelvic pathology. We did not find any previous case in the literature that reports small-bowel accumulation of Tc-99m-MDP in children. The mechanism of this accumulation is unclear, but we assume that the same mechanism and factors that were reported to enhance the localization of the radiotracer in the colon may apply to the small bowel. The accumulation of the radiotracer in our case is focal and may be explained by focal histological disturbances of a small-bowel segment that contributed to excretion of the radiotracer from the blood-to-bowel lumen. It may also be that the radiotracer reached the small-bowel lumen through liver excretion (related to the radiopharmaceutical) or was excreted in a proximal small-bowel segment and was then seen in delayed images in the pelvic small bowel.