Improved techniques in radionuclide imaging of prostatic lymph nodes

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.

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

The major application of nuclear imaging techniques to the genital tract is pertechnetate scintigraphy for evaluation of the acute hemiscrotum. Within a few years of the first descriptions of scrotal imaging, this technique achieved recognition as a valuable, even indispensable, emergency diagnostic procedure in this context; its validity has since been well confirmed in hundreds of reported cases. Because it is an established procedure with widely recognized applications, its discussion will occupy most of this article. Other nuclear procedures, less widely used either because they are investigative or applicable to smaller patient populations, will be more briefly described.

Clinical experience with intra lymphatic administration of 111In-labelled monoclonal antibody PAY 276 for the detection of pelvic nodal metastases in prostatic carcinoma

The ability of 111In-PAY 276 (anti prostatic acid phosphatase antibody) in detecting pelvic lymph node metastasis following bipedal intra lymphatic administration was studied in five patients with carcinoma of the prostate. The labeled antibody was injected directly into the lymphatics of each foot. Planar and tomographic images radioactivity content of lymph nodes resected during staging pelvic lymphadenectomy were compared to the histologic and immunoperoxidase findings. Radioactivity in pelvic lymph nodes was prominently seen within 20 min of injection and was present 16 days later. Persistent accumulation of tracer in the lymphatics of the lower extremities was also observed in all patients 16 days post injection. Radioactivity counts in tumor-free lymph nodes were higher than in tumored lymph nodes resected. Our results demonstrate that intra lymphatic administration of 111In-labeled PAY 276 monoclonal antibody has major technical limitations, and that further research directed at the causes of tracer accumulation in the lymphatics and tumor-free lymph nodes is required.

Abdominal lymphoscintigraphy: an effective substitute for lymphography?

Abdominal lymphoscintigraphy is a quick, easy, cheap and relatively non-invasive technique. In our study it appeared to be as accurate as lymphography, giving a positive correlation in 25 out of 32 patients (78%). In 11% of cases the lymphoscintigram detected an abnormality of lymph node function before macroscopic morphological change was seen in the lymphogram, indicating that in some instances lymphoscintigraphy is more sensitive than lymphography. The reason for this is unknown, although possible mechanisms are discussed and these are the subject of current further study. We believe this to be the first report of lymphoscintigraphy being more sensitive than lymphography for detecting lymph node disease.

Rectal lymphoscintigraphy

Regional lymph nodes of the rectum are not demonstrable by pedal lymphoscintigraphy. We have evaluated the technique of rectal lymphoscintigraphy, using a technique similar to that which has been used in the assessment of lymph nodes in breast and prostatic cancer. Thirty-five patients were studied: ten normal subjects and 25 patients with rectal cancer. In normal subjects, the lymph nodes accompanying the superior hemorrhoidal artery and the inferior mesenteric artery are demonstrable in succession; after three hours the aortic lymph nodes are demonstrable. The 25 patients with rectal cancer underwent resection of their primary tumor and the stage was defined according to Dukes (1932). In five patients (stage A) no alteration was demonstrable. In 11 patients (stage B) the demonstration of regional lymph nodes was delayed vs. the control group. In nine cases (stage C) the demonstration of regional lymph nodes was delayed and defective versus the control group.

Iliopelvic lymphoscintigraphy

In patients with genitourinary cancers, it is critically important that lymph node metastases be detected prior to surgery. Information regarding the status of these nodes will influence the type and extent of therapy. Radiologic tests currently available for lymph node imaging--contrast lymphangiography, ultrasound, and computed tomography--are sometimes associated with a high false-negative rate. Iliopelvic lymphoscintigraphy, when performed following bilateral perianal injections of 99mTc-antimony trisulfide colloid, offers a physiologic method for visualizing these nodes and allows demonstration of the internal iliac chain, often not visualized on contrast lymphangiographic studies. Additionally, data from initial patient trials suggest that this technique offers a clinically acceptable level of sensitivity and specificity. This article details the methodology of the technique, and addresses reproducibility, sensitivity, specificity, and image interpretation.

The diagnosis and detection of urogenital cancers

Previously, histologic precision in the diagnosis of urologic cancers had, for some time, remained stable. More recently, variations in classifications of testis tumors, prostate cancer, and to some degree, bladder tumors, have been introduced. Most systems have in concurrence a desire or an attempt to infer better prognostic assessment in the overall results to treatment. With the advent of additional biological markers or direct enzymatic measurements, e.g., in prostate cancer, further improvements in identifying at risk populations, responses to treatment, and possible indications for variations in treatment, have ensued. These developments alone unquestionably mark the greatest area of change in the recent decade. The extent of disease assessment prior to definitive therapy, whether by arteriography, ultrasound, CAT scanning, or an occasional lymphangiography, has also influenced or modified treatment decisions. For continuing care and follow-up, several of these noninvasive techniques are now becoming included in the more standard approaches. Noninvasive techniques have been introduced for the therapy of renal tumors such as inducing infarction of the primary tumor. Endoscopic ultrasonic techniques have been particularly useful in assessing the size of pelvic tumors and response to treatment, even in detection of unexpected multiple primaries or metastatic extensions. Overall, the precision in urologic cancer, both for diagnostic and detection purposes, has been increased with these introductions.