Vas deferens infiltration by prostate cancer on prostate-specific membrane antigen-targeted ¹⁸F-DCFPyL positron emission tomography/computed tomography: A unique visual pattern

Keywords

¹⁸F-DCFPyL - positron emission tomography/computed tomography - prostate cancer - prostate-specific membrane - vas deferens

Introduction

Prostate cancer (PCa) is the most common noncutaneous malignancy in men and is a leading cause of cancer-related deaths. A number of prognostic features of primary PCa can portend the possibility of treatment failure including high Gleason score, elevated prostate-specific antigen (PSA) level, and direct extension of the tumor beyond the confines of the prostate into the periprostatic soft tissues (pT3a) or the seminal vesicles (pT3b). Although rare, invasion of the vasa deferentia, the paired tubular structures that carry sperm from the epididymis to the urethra, is also a poor prognostic feature of PCa and also falls under the pT3b classification.[1]

In recent years, the ability to image PCa has improved dramatically as a result of the development of multiple targeted radiotracers for positron emission tomography (PET) imaging. These agents localize to PCa by taking advantage of the metabolic properties of the tumor cells (e.g. 1-amino-3-fluorine 18-fluorocyclobutane-1-carboxylic acid) or by interactions with cell surface receptors that are overexpressed in PCa (e.g. prostate-specific membrane antigen [PSMA]-targeted radiotracers such as ⁶⁸Ga-PSMA-11 and ¹⁸F-DCFPyL and gastrin-releasing peptide receptor-targeted compounds such as ⁶⁸Ga-RM2). To date, the PSMA-targeted agents have been the most extensively studied and have been found to have very high sensitivities for the detection of suspected sites of PCa.[2],[3] Due to these high sensitivities, the PSMA PCa literature now includes reports of a number of unusual sites of recurrent or residual PCa in the pelvis.[4],[5],[6] Herein, we report an as yet undescribed pattern of disease involvement of the vas deferens in which curvilinear radiotracer uptake outlining the intrapelvic course of the vas deferens was visualized with PSMA-targeted ¹⁸F-DCFPyL PET/computed tomography (CT).

Case Report

The patient was a 71-year-old man who was diagnosed with PCa after presenting with a PSA level of 5.5 ng/mL 5 years before undergoing PSMA-targeted imaging. A prostate biopsy at that time revealed PCa with a Gleason score of 4 + 3 = 7. The patient subsequently underwent a radical retropubic prostatectomy confirming PCa with vasa deferentia invasion, bilateral seminal vesicle invasion, multifocal extraprostatic extension, and lymphovascular invasion. In addition, the patient was found to have positive resection margins at the bilateral vas deferens and seminal vesicles. Initial PSA following prostatectomy was 0.2 ng/mL. The patient was then treated with salvage external beam radiotherapy with 8 months of combined androgen blockade. At that time, his PSA became transiently undetectable. Two years after surgery, the patient experienced a biochemical recurrence with his PSA rising to 12.2 ng/mL.

Workup for his elevated PSA included magnetic resonance imaging of the pelvis and a Na ¹⁸F PET/CT scan, neither of which demonstrated a site of disease. He was then treated on a clinical trial with degarelix and his PSA again became undetectable. However, following completion of degarelix therapy, the patient's PSA again rose to 4.1 ng/mL. This prompted an additional workup with conventional imaging including a contrast-enhanced CT of the chest, abdomen, and pelvis as well as a99m Tc-MDP bone scan, neither of which revealed radiographic evidence of disease. The patient was then enrolled in a prospective trial evaluating the clinical utility of PSMA-targeted ¹⁸F-DCFPyl PET/CT. The patient signed written informed consent prior to imaging.18 F-DCFPyL PET/CT was conducted under a Food and Drug Administration Investigational New Drug application (IND #121064) with an imaging protocol as previously described.[7]

The uptake of ¹⁸F-DCFPyL in this patient was in a pattern not previously reported. The entire intrapelvic course of the left vas deferens was outlined with abnormal intense (maximum lean body mass-corrected standardized uptake value of 11.8) radiotracer uptake [Figure 1] and [Figure 2]. The uptake was in a curvilinear distribution extending from the left inguinal canal, through the left side of the pelvis, and ending in the left prostate bed, presumably at the site of the left vas deferens positive margin. A small focus of uptake was also present on the contralateral side and may have been related to the positive right vas deferens margin. Otherwise, no other sites of abnormal radiotracer uptake to suggest additional sites of disease were appreciated on the scan.

Figure 1 (a) Right anterior oblique maximum intensity projection of the pelvis from a ¹⁸F-DCFPyL PET scan in the 71-year-old male patient with prior history of prostatectomy and previous treatment with androgen deprivation who is described in this case report. Note the curvilinear distribution of radiotracer in the left pelvis (red arrows) that outlines the expected intrapelvic course of the left vas deferens. (b) The same maximum intensity projection as in (a) but with a red line demarcating the approximate location of the intrapelvic left vas deferens

Figure 2 (a-h) Axial fused ¹⁸F-DCFPyL positron emission tomography/computed tomography images of the left pelvis arranged from inferior to superior (a-d) and from superior to inferior (e-h). The uptake in the left vas deferens was in a curvilinear distribution extending from the left inguinal canal (red arrows in [a-d]), through the left side of the pelvis (red arrows in e-g), and ending in the left prostate bed (red arrow in h), presumably at the site of the left vas deferens positive margin

Discussion

The increasingly widespread availability of molecular imaging for the detection of sites of PCa has brought to light new patterns of recurrent, residual, and metastatic disease. It is imperative for both imaging specialists and clinicians to be aware of these patterns and to recognize their features. In this report, we describe a novel pattern of ¹⁸F-DCFPyL uptake outlining the entire intrapelvic course of the left vas deferens in a patient with history of prior prostatectomy. The curvilinear morphology of this apparent site of disease is a unique appearance that has not previously been reported. Recognition of this pattern of radiotracer uptake and its significance is important as the unusual configuration could be mistaken for an imaging artifact. Indeed, the correct interpretation of this finding can only be made in the context of an understanding of the cross-sectional anatomy of the vas deferens.

While pathologic confirmation of disease in the patient's left vas deferens is necessary to confirm the diagnosis of PCa, PSMA-targeted agents have been repeatedly shown to have exceedingly high specificities.[8],[9] In addition, many of the potential pitfalls for interpretation of these scans have been extensively described.[10] As such, the possibility of a false positive, in light of the patient's known history of a positive left vas deferens surgical margin, is quite low. In the future, further careful examination of patients undergoing PSMA-targeted PET imaging for a variety of PCa-related indications will ensure that other heretofore unknown patterns of radiotracer uptake will be well described and widely known to those interpreting these scans.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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