PET-CT and PET-MR in urological cancers other than prostate cancer: An update on state of the art

A multimodality review of male urethral imaging: pearls and pitfalls with an update on urethral stricture treatment

Optimum radiological assessment of the male urethra requires knowledge of the normal urethral anatomy and ideal imaging techniques based on the specific clinical scenario. Retrograde urethrography is the workhorse examination for male urethral imaging, usually utilized as the initial, and often solitary, modality of choice not only in the setting of trauma, but also in the pre- and post-operative evaluation of urethral strictures. There is, however, growing interest in utilization of ultrasound and magnetic resonance for evaluation of the male urethra owing to lack of ionizing radiation and improved delineation of the adjacent tissue. We review the various modalities utilized for imaging of the male urethra for a variety of known or suspected disorders, and provide an update on current treatments of urethral strictures. Additionally, we detail the key information needed by urologists to guide management of urethral strictures. We conclude with a brief discussion of neophallus urethral diseases following female-to-male sexual confirmation surgery.

Bone scan with technetium 99m-methyl diphosphonate, the missing link in the initial staging of muscle-invasive bladder carcinoma

BACKGROUND

Accurate staging is crucial to determine the type of treatment for patients with bladder cancer (BCa), especially in high-risk cases. We aimed to assess the role of bone scan in the initial staging of muscle-invasive bladder carcinoma (MIBC).

MATERIAL AND METHODS

Forty-five patients with MIBC were referred to our tertiary clinic to perform a technetium 99m-methyl diphosphonate (Tc99m-MDP) bone scan from January 2019 to March 2020. The patients underwent bone scintigraphy with pelvic SPECT/CT before radical cystectomy. Whole-body scanning was performed 4 hours after Tc99m-MDP injection in both anterior and posterior views. Since the most common bone involvement site in these patients is the pelvic bones and the spine, pelvic SPECT/CT was performed in all patients.

RESULTS

Frequency of skeletal metastasis was 26.7%. Only 19% of the metastases were detected by previous pelvic CT/MRI images performed for routine staging. All the reported skeletal metastases by previous anatomical imaging methods were detected in the bone scan. There was no statistically significant correlation between bone metastasis and the patient's age, lymph nodes metastasis (LNM), hydronephrosis, and muscle-invasive type. The mean serum calcium level was 8.7 ± 0.57 in patients with bone metastasis and 8.87 ± 0.99 in patients without bone metastasis, which was not statistically significant.

CONCLUSION

Bone scan has higher diagnostic performance than conventional imaging methods for detecting bone metastases. It changed the management plan in 8.8% of our patients, so we conclude that performing a whole-body bone scan in the initial staging of MIBC would be helpful.

Use of F-18 FDG PET/CT Through Delayed Diuretic Imaging for Preoperative Evaluation of Upper Urinary Tract-Occupying Lesions

Purpose

To evaluate the value of F-18 FDG PET/CT in the differentiation of malignant and benign upper urinary tract-occupying lesions.

Patients and Methods

64 patients with upper urinary tract-occupying lesions underwent F-18 FDG PET/CT at RenJi Hospital from January 2015 to February 2019 in this retrospective study. Of the 64 patients, 50 patients received nephroureterectomy or partial ureterectomy; 14 patients received ureteroscopy and biopsy. The comparisons of PET/CT parameters and clinical characteristics between malignant and benign upper urinary tract-occupying lesions were investigated.

Results

Of the 64 patients, 49 were found to have malignant tumors. Receiver operating characteristic analysis determined the lesion SUVmax value of 6.75 as the threshold for predicting malignant tumors. There were significant associations between malignant and benign upper urinary tract-occupying lesions and SUVmax of lesion (P<0.001), lesion size (P<0.001), and patient age (P=0.011). Multivariate analysis showed that SUVmax of lesion (P=0.042) and patient age (P=0.009) as independent predictors for differentiation of malignant from benign upper urinary tract-occupying lesions. There was a significant difference in tumor size between the positive (SUVmax >6.75) and negative (SUVmax ≤6.75) PET groups in 38 of the 49 patients with malignant tumors.

Conclusion

The SUVmax of lesion and patient age is associated with the nature of upper urinary tract-occupying lesions. F-18 FDG PET/CT may be useful to distinguish between malignant and benign upper urinary tract-occupying lesions and determine a suitable therapeutic strategy.

Imaging of Bladder Cancer: Standard Applications and Future Trends

The evolution in imaging has had an increasing role in the diagnosis, staging and follow up of bladder cancer. Conventional cystoscopy is crucial in the diagnosis of bladder cancer. However, a cystoscopic procedure cannot always depict carcinoma in situ (CIS) or differentiate benign from malignant tumors prior to biopsy. This review will discuss the standard application, novel imaging modalities and their additive role in patients with bladder cancer. Staging can be performed with CT, but distinguishing between T1 and T2 BCa (bladder cancer) cannot be assessed. MRI can distinguish muscle-invasive from non-muscle-invasive tumors with accurate local staging. Vesical Imaging-Reporting and Data System (VI-RADS) score is a new diagnostic modality used for the prediction of tumor aggressiveness and therapeutic response. Bone scintigraphy is recommended in patients with muscle-invasive BCa with suspected bony metastases. CT shows low sensitivity for nodal staging; however, PET (Positron Emission Tomography)/CT is superior and highly recommended for restaging and determining therapeutic effect. PET/MRI is a new imaging technique in bladder cancer imaging and its role is promising. Texture analysis has shown significant steps in discriminating low-grade from high-grade bladder cancer. Radiomics could be a reliable method for quantitative assessment of the muscle invasion of bladder cancer.

Delayed 18F-FDG PET/CT Appearance of Urachal Adenocarcinomas

Background

Urachal carcinoma is a rare urological malignancy. Use of ¹⁸F-FDG PET/CT in urological oncology has developed slowly because of the urinary elimination of ¹⁸F-FDG. We investigated whether delayed postdiuretic ¹⁸F-FDG PET/CT could be used for diagnosing urachal carcinoma.

Methods

This retrospective study included 6 patients who underwent delayed postdiuretic ¹⁸F-FDG PET/CT for the evaluation of urachal carcinoma. The delayed postdiuretic PET/CT parameters and clinical characteristics of urachal carcinoma were investigated.

Results

There was no significant difference in the SUVmax between the primary tumors and the urine in the bladder before delayed diuresis (25.4 ± 19.5 vs. 42.9 ± 31.1, P=0.18). However, the SUVmax of the primary tumors was significantly higher than the SUVmax of urine after delayed diuresis (25.4 ± 19.5 vs. 3.5 ± 1.6, P=0.002). Diuretic ¹⁸F-FDG PET/CT was positive in all patients when compared with normal liver tissues or urine after delayed diuresis. The SUVmax, TLR, and TUR of the primary tumors were 25.4 (range: 7.2–58.9), 7.0 (range: 1.8–14.7), and 6.8 (range: 3.8–11.3), respectively. Delayed postdiuretic ¹⁸F-FDG PET/CT had a negative predictive value of 100% (5/5) for predicting lymph node metastasis. One patient received chemotherapy after radical resection of urachal carcinoma because ¹⁸F-FDG PET/CT found lung metastases, and one patient only received chemotherapy because PET/CT found peritoneal and skeletal metastases.

Conclusions

Delayed postdiuretic ¹⁸F-FDG PET/CT is a useful tool for the preoperative evaluation of urachal carcinoma. ¹⁸F-FDG PET/CT may improve clinical decision making and management of urachal carcinomas.

Delayed post-diuretic 18F-FDG PET/CT for preoperative evaluation of renal pelvic cancer

Background: Application of ¹⁸F^-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) in urological oncology was relatively slowly due to the urinary elimination of ¹⁸F-FDG. We investigated whether delayed post-diuretic ¹⁸F-FDG PET/CT could be used for diagnosing renal pelvic cancer.

Methods: 51 patients were included who underwent delayed post-diuretic ¹⁸F-FDG PET/CT for detecting renal pelvic space-occupying lesions. The comparations of delayed PET/CT parameters and clinical characteristics between renal pelvic cancer and benign polyp were investigated.

Results: Among the 51 patients, 47 were found to have renal pelvic urothelial carcinoma, and 4 had benign polyp. ROC analysis identified the lesion maximum standardized uptake value (SUVmax) of 6.2 as the optimal cut-off value to distinguish from renal pelvic urothelial carcinoma to benign polyp. With the SUVmax cut-off of 6.2, the sensitivity, and specificity for predicting of renal pelvic urothelial carcinoma were 91.5% (43/47), and 100% (4/4). We also found a significant difference in tumor size between the positive (SUVmax > 6.2) and negative (SUVmax ≤ 6.2) PET groups in renal pelvic cancers. In patients with tumor size < 1.1 cm, the probability of being in the negative PET group was 75%. In such patients, a substantial proportion of renal pelvic cancer demonstrated negative SUVmax similar to that in patients with benign polyp.

Conclusion: Delayed ¹⁸F-FDG PET/CT could be used for differentiating renal pelvic cancer from benign polyp. In patients with small tumor size, renal pelvic cancer may present low ¹⁸F-FDG uptake, mimicking the metabolic phenotypes of patients with benign polyp.

Diagnosis of bladder cancer using 18F-labeled α-methyl-phenylalanine tracers in a mouse model

OBJECTIVE

Although 2-¹⁸F-fluoro-2-deoxy-glucose (¹⁸F-FDG) has established roles in the diagnosis of a variety of cancers, it has limited value in the detection of primary/recurrent lesions in the bladder, mainly because of interference by the pooled radioactivity in the urine. Our previous study revealed promising properties of L- and D-2-¹⁸F-α-methyl-phenylalanine (2-¹⁸F-FAMP) as radiotracers; i.e., their rapid blood clearance and low renal accumulation. In the present study we evaluated the utility of L- and D-2-¹⁸F-FAMP for imaging bladder cancer in a mouse model.

METHODS

We used the human bladder cancer cell line HT1376 to prepare a bladder cancer xenograft model in mice bearing both orthotopic and subcutaneous tumors. Biodistribution and PET imaging studies were performed at 1 and 3 h after injection of L-2-¹⁸F-FAMP or D-2-¹⁸F-FAMP. ¹⁸F-FDG was used as a control.

RESULTS

At 1 h after injection, greater accumulations of both L-2-¹⁸F-FAMP and D-2-¹⁸F-FAMP were observed in the orthotopic tumors compared to ¹⁸F-FDG. The orthotopic tumor-to-muscle ratio of D-2-¹⁸F-FAMP was significantly higher than that of ¹⁸F-FDG (p < 0.01), because of the rapid blood clearance of D-2-¹⁸F-FAMP. L-2-¹⁸F-FAMP showed the highest subcutaneous tumor-to-muscle ratio (p < 0.01) due to its high subcutaneous tumor uptake. Compared to L-2-¹⁸F-FAMP, D-2-¹⁸F-FAMP exhibited faster clearance and lower kidney accumulation. In the PET imaging studies, L- and D-2-¹⁸F-FAMP both clearly visualized the orthotopic bladder tumors at 1 h after injection.

CONCLUSION

Our study showed that L-2-¹⁸F-FAMP and D-2-¹⁸F-FAMP have the potential to detect bladder cancer.