CLINICAL HISTORY
A 79-year-old man was diagnosed with prostate cancer in 1993 after a transurethral resection of the prostate (TURP). The patient had a Gleason score of 5 and was initially treated with low-dose-rate radioactive seed implants. PSA values decreased from 10 ng/ml to undetectable levels. In 2004, his PSA began to rise again.
FINDINGS
Subsequent CT and Tc-99m methylenephosphonate (MDP) bone scan (see legend) demonstrated osteoblastic metastases within the lumbar spine and pelvis. Multiple enlarged pelvic lymph nodes included a significantly enlarged left iliac chain node (5.3 x 4.8 x 7.7 cm) with clusters of calcification. This enlarged lymph node demonstrated Tc-99m MDP retention on bone scan, likely related to the calcification.
DIAGNOSIS
Metastatic prostate cancer.
DISCUSSION
The exact mechanism of technetium-labeled phosphonate uptake in a bone scan is not completely understood. It is thought that the phosphonate molecule is chemiabsorbed onto the calcium portion of hydroxyapatite, located on the surface of bone.
The major factors affecting this absorption include osteoblastic activity and skeletal vascularity, with preferential uptake at sites of active bone formation. Mechanisms that may lead to increased extraosseous Tc-99m–labeled phosphonate uptake include extracellular fluid expansion, enhanced regional vascularity and permeability, and elevated tissue calcium concentration.
There have been numerous reports of extraosseous Tc-99m–labeled phosphonate accumulation in a variety of clinical settings including hepatic metastases from colon, breast, and other mucinous carcinomas, ganglioneuroblastoma, a benign intrapulmonary calcified focus, plasma cell granuloma, benign cystic teratoma, ovarian carcinoma and its soft tissue metastases, intracranial Sturge-Weber syndrome, cutaneous malignant melanoma metastases in an inguinal lymph node, lymph node metastases of small cell carcinoma of the esophagus, and focal uptake in a gossypiboma (a retained surgical sponge).
Prior to this report, one case of increased phosphonate uptake due to calcification within the prostate has been published. However, to our knowledge, no cases of increased uptake in a patient with metastatic prostate cancer to lymph nodes containing calcification have been reported.
Submitted by Dr. Michael E. Witkosky, Dr. Alan D. Waxman, and Dr. Louise E.J. Thomson, all in the division of nuclear medicine, department of imaging at Cedars-Sinai Medical Center in Los Angeles, CA.
BIBLIOGRAPHY
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