Testicular scanning and other applications of radionuclide imaging of the genital tract

Functional Imaging of Testicular Torsion

This article discusses the current clinical role and scope of functional radionuclide imaging using testicular perfusion scintigraphy with 99mTc-pertechnetate in patients presenting with an acute hemiscrotum for an early and reliable diagnosis of testicular torsion. The technique of testicular perfusion scintigraphy is described, and the characteristic findings are detailed with examples. The imaging characteristics of the various phases of testicular torsion and its differentiation from epididymitis and/or epididymo-orchitis and the other related conditions presenting as an acute hemiscrotum are detailed. In some cases, further evaluation by SPECT imaging increases the clarity and accuracy of diagnosis and, on occasion, hybrid SPECT/CT in selected complicated cases improves the diagnostic yield of the perfusion scintigraphy. Ultrasonographic and color Doppler findings are described concurrently with the scintigraphic findings. The several case examples presented demonstrate the additional clinical benefit of complementing functional and structural imaging for improving the sensitivity, specificity and accuracy of testicular imaging in the diagnosis.

Interesting Signs in Nuclear Medicine

Classic radiological and nuclear medicine signs have been reported extensively because of a myriad of pathophysiological processes. When encountered, they aid in diagnosis of conditions and add confidence for the reader, at times even hinting at a specific diagnosis. The naming of signs is commonly associated with objects from everyday life to establish familiarity with visual findings. Association of signs and disease comes with regular practice and improves understanding of the image and its underlying cause. In this article, we have collated nuclear medicine signs reported in the literature since 1970.

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.

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.

A selective approach to the treatment of acute scrotum in children

To determine a reliable clinical approach to the problem of acute scrotum (AS) in children and identify patients who require emergent surgical intervention, 65 boys with the diagnosis of AS were studied. The mean age was 11 years. Acute orchitis/epididymitis was diagnosed in 42 (64.6%), torsion of the testis in 12 (18.5%), and torsion of the appendix testis in 5 (7.7%). A testicular radionuclide scan was the most reliable diagnostic tool, being positive in all 12 cases of torsion of the testis. Eighteen patients underwent scrotal exploration. Detorsion and bilateral orchidopexy was performed in 12, excision of a necrotic appendix testis in 5, and evacuation of a scrotal hematoma in 1. The outcome of the involved testis at follow-up examination was excellent, with only 1 child developing testicular atrophy. This study stresses the reliability of the selective approach for the treatment of the AS in children.

Scintigraphic evaluation of testicular torsion and acute epididymitis

PURPOSE OF THE STUDY

To evaluate the effectiveness of testicular scintigraphy in differentiating testicular torsion from acute epididymitis.

METHOD

14 out of 17 patients previously screened by urologist were referred for testicular scintigraphy. Preoperative diagnosis was made based on dynamic and static image findings. Close follow-up was done and final diagnosis was confirmed on the basis of operative findings or relief of symptoms after conservative management.

RESULTS

Eight of the nine patients with a photopenic area in the hemiscrotum were confirmed surgically as having testicular torsion. One patient was diagnosed as having an inflammatory process. Relief from symptoms after conservative management was noted in three patients with increased activity on the affected side and in two others whose uptake patterns were not different from the unaffected side.

CONCLUSION

Testicular scintigraphy is effective in differentiating testicular torsion from acute inflammation when all other scrotal anomalies have been eliminated.

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

Scintigraphic techniques for evaluation of impotence are still evolving. Blood pool studies are most useful in assessing the integrity of arterial inflow, but may also be used to generate indices of venous leak. A non-imaging version of this test may represent a simple and cost-effective alternative. Washout of intracavernosal xenon during erection seems the most useful method of testing venous integrity. Washout using Tc-RBC may emerge as a convenient alternative to the more technically difficult xenon examinations. Development of more effective pharmacologic stimuli may further improve the utility of this quantitative and physiologic examination.

Radionuclide genital imaging

Despite the emergence of newer cross-sectional imaging approaches, radionuclide techniques have maintained a significant role in genital imaging. While ultrasound is clearly superior for evaluation of scrotal anatomy, radionuclide scrotal imaging remains the most effective method for differentiating between testicular torsion and epididymitis. Labeled red blood cells have been used for varicocele detection in infertile men. Since radionuclide techniques can demonstrate the physiologic status of organs, they play a useful role in evaluating men with impotence (penile scan) and infertile women whose tubal patency is in question (radionuclide hysterosalpingogram).