The role of nuclear medicine in the evaluation of the male genital tract

Nuclear Medicine Studies of the Prostate, Testes, and Bladder

During the last decade, there has been a significant advancement in imaging of urologic diseases. Transrectal ultrasound (TRUS), computerized tomography (CT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and positron emission tomography (PET) are still experiencing new developments in urology. Despite these many technological advances, the initial diagnostic procedure for a patient with suspected prostate cancer (PC) is multiple site blind prostate biopsies. There is a need for a noninvasive metabolic imaging modality to direct the site of biopsy to decrease the sampling error. MRS seems promising but as it is a costly and more time-consuming test, further studies are needed to evaluate its clinical utility. Currently, PET does not play any role to direct biopsy. Acetate and choline appear to be better tracers than FDG for the detection of a prostate lesion, however, further well-organized studies are needed before any of these agents can be used clinically. Incidental detection of intense focal uptake in the prostate during whole body PET scanning should be evaluated with prostate-specific antigen (PSA) and TRUS-guided biopsy. Although FDG is inferior to other tracers for primary staging, it may be useful in selected patients with suspected high-grade cancer. The role of ProstaScint scan is still controversial for detection of recurrent PC. This study may be helpful for evaluating nodal metastases when PSA is elevated and bone scan is negative. Bone scan remains the study of choice when bone metastases are suspected (PSA>15-20 ng/mL+/-bone pain). Acetate and choline provide better accuracy than FDG in the detection of local soft tissue disease, nodal involvement, and distant metastases. High FDG uptake may be indicative of more aggressive and possibly androgen-independent disease. PET/CT with any of the above PET tracers will most likely be preferred to the PET scan alone due to better localization of a hot lesion in PET/CT. Nuclear medicine studies also have been used to evaluate acute scrotum and testicular neoplasms. Scrotal scintigraphy has lost its popularity to Doppler ultrasound in the evaluation of the acute scrotum. In testicular tumors, FDG-PET appears to be superior to conventional imaging modalities in initial staging, detection of residual/recurrence, and monitoring treatment response. Tumor markers after treatment occasionally are elevated and cannot locate the site of recurrence, FDG-PET can play a very important role in this regard. Nuclear medicine studies also have been used to evaluate diseases of the urinary bladder. Radionuclide cystography is more sensitive and has less than 1/20 the radiation exposure of the conventional contrast enhanced micturating cystourethrogram (MCU). However, the utility of FDG-PET in the evaluation of bladder cancer seems to be limited to the evaluation of distant metastases. 11C-Methionine and choline may be a better option for local and nodal disease due to their negligible excretion in the urine.

Comparison of radionuclide imaging and ultrasonography in the differentiation of acute testicular torsion and inflammatory testicular disease

PURPOSE

Torsion of the testis is a urologic emergency that requires early diagnosis and prompt surgical treatment for testicular survival. However, the early differential diagnosis of acute testicular torsion from epididymitis or orchitis is often difficult. The aim of this retrospective study was to evaluate and compare the value of Tc-99m pertechnetate radionuclide imaging and ultrasonography in the differentiation of acute testicular torsion and inflammatory testicular diseases.

METHODS

Twenty patients (age range, 5 to 38 years) with possible acute testicular torsion from July 2000 to July 2001 were enrolled in this study. Ultrasonography was performed in all patients in the emergency room. Within 3 hours of ultrasonography, radionuclide imaging was also performed after intravenous injection of 5 to 15 mCi Tc-99m pertechnetate in the forearms. All of the patients with clinically suspected acute testicular torsion underwent surgery. The surgical findings and pathologic reports of these patients were reviewed and definite diagnoses were established. None of the other patients had surgery and were followed clinically for at least 1 month after ultrasonography and radionuclide imaging.

RESULTS

Four patients with testicular torsion, 13 patients with inflammatory testicular disease, and three healthy persons had a final surgical and pathologic diagnosis or clinical follow-up, and all were accurately diagnosed by Tc-99m pertechnetate radionuclide imaging. In contrast, ultrasonography was less accurate in the diagnosis and differentiation of acute testicular torsion from inflammation. Only 1 of 4 patients with testicular torsion, 5 of 13 patients with inflammatory testicular disease, and 2 of 3 healthy persons were diagnosed by ultrasonography.

CONCLUSIONS

The results indicate that Tc-99m pertechnetate radionuclide imaging is a more useful and accurate imaging method than ultrasonography in the detection and differentiation of acute testicular torsion from inflammatory testicular disease in patients with acute scrotal pain.

Relative blood volume measurements by magnetic resonance imaging facilitate detection of testicular torsion

RATIONALE AND OBJECTIVES

The authors determine the utility of relative blood volume measurements (rBV) using a blood pool marker for magnetic resonance imaging (MRI) in detection of early testicular torsion.

METHODS

Testicular torsion was induced in rats by counterclockwise 720 degrees rotation and fixation of the testis in the scrotum. MPEG-PL-DTPA-Gd enhanced MRI (30 mumol Gd/kg bolus injection) was performed 1 hour after torsion at 1.5 T using fat-suppressed three-dimensional fast spoiled gradient-recalled sequence for relative blood volume measurement and three-dimensional time-of-flight sequence for MR angiography (MRA).

RESULTS

The rBV of the torqued testes was significantly lower (13.3% +/- 13.5%) than that of testes with sham operation (97.7% +/- 5.3%; P < 0.05). Rats with testicular torsion showed larger regions of ischemia than did animals with sham operation (63.4% +/- 13.0% versus 4.0% +/- 2.8% of all pixels in testis; P < 0.01). The MRA of testicular torsion showed engorgement of the distal testicular vein as a sign of venous compression or total disappearance of the testicular vein, indicating arterial insufficiency.

CONCLUSIONS

The authors conclude that MPEG-PL-DTPA-Gd can be used to obtain functional (rBV), morphologic (tunica enhancement), and angiographic (venous engorgement, arterial compromise) findings that should improve the diagnosis of testicular torsion in the acute setting.