Inguinal lymph node metastases from prostate cancer: clinical, pathology, and multimodality imaging considerations

Abstract

Objective: To investigate clinical, pathology, and imaging findings associated with inguinal lymph node (LN) metastases in patients with prostate cancer (PCa).

Materials and methods: This was a retrospective single-center study of patients with PCa who underwent imaging and inguinal LN biopsy between 2000 and 2023. We assessed the following aspects on multimodality imaging: inguinal LN morphology; extrainguinal lymphadenopathy; the extent of primary and recurrent tumors; and non-nodal metastases. Imaging, clinical, and pathology features were compared between patients with and without metastatic inguinal LNs.

Results: We evaluated 79 patients, of whom 38 (48.1%) had pathology-proven inguinal LN metastasis. Certain imaging aspects- short-axis diameter, prostate-specific membrane antigen uptake on positron-emission tomography, membranous urethra involvement by the tumor, extra-inguinal lymphadenopathy, and distant metastases-were associated with pathology-proven inguinal LN metastases (p < 0.01 for all). Associations with long-axis diameter, fatty hilum, laterality, and uptake of other tracers on positronemission tomography were not significant (p = 0.09-1.00). The patients with metastatic inguinal LNs had higher prostate-specific antigen levels and more commonly had castration-resistant PCa (p < 0.01), whereas age, histological grade, and treatment type were not significant factors (p = 0.07-0.37). None of the patients had inguinal LN metastasis in the absence of locally advanced disease with membranous urethra involvement or distant metastasis.

Conclusion: Several imaging, clinical, and pathology features are associated with inguinal LN metastases in patients with PCa. Isolated metastasis to inguinal LNs is extremely rare and unlikely to occur in the absence of high-risk imaging, clinical, or pathology features.

Keywords: Biopsy; Lymph nodes/pathology; Magnetic resonance imaging; Positron emission tomography computed tomography; Prostatic neoplasms/diagnostic imaging; Urethra/pathology.

Figure 1.

Flow chart of the patient selection process.

Figure 2.

PSMA PET/CT and prostate MRI of a 66-year-old man with newly diagnosed ISUP grade group 5 PCa. PSA was 18.2 ng/mL at baseline. A: Maximumintensity projection PSMA PET/CT image showing a few enlarged and radiotracer-avid pelvic and left inguinal LNs, as well as the primary prostate tumor. B: Axial fused PSMA PET/CT shows the biopsied left inguinal LN (arrow) measuring 1.2 × 1.0 cm with an SUVmax of 27.8. C: Prostate MRI showing an apically located primary prostate tumor (arrowheads) encasing the membranous urethra and in contact with lower anterior rectum. D: Axial fused PSMA PET/CT showing a metastatic right mesorectal LN (solid circle) together with a superior rectal LN (broken circle in A). No suspicious pelvic LNs were noted at the typical sites (e.g., external, internal, common iliac, retroperitoneal, etc.).

Figure 3.

Fluciclovine PET/CT and prostate MRI of an 81-year-old man with ISUP grade group 4 PCa who underwent RT followed by androgen-deprivation therapy and multiple systemic treatments, the tumor subsequently becoming castration-resistant. PSA was 7.0 and 0.7 ng/mL at baseline and at the time of imaging, respectively. A: Maximum-intensity projection fluciclovine PET/CT image showing numerous enlarged and radiotracer-avid bilateral inguinal, pelvic, and lower retroperitoneal LNs. B: Axial fused PET/CT showing the biopsied right inguinal LN (solid arrow) measuring 5.1 × 4.5 cm with an SUVmax of 16.3. C: Prostate MRI showing a locally recurrent mass (broken arrow) involving vesicourethral anastomosis. D: Axial fused PET/CT at a different level showing fluciclovine-avid bone metastasis at the right ischium (circle). Biopsy revealed a metastatic inguinal LN.

Figure 4.

CT and prostate MRI of a 67-year-old man with newly diagnosed ISUP grade group 4 PCa. PSA was 19.2 ng/mL at baseline. A: Axial CT showing bilateral enlarged inguinal LNs, including the biopsied one on the left (arrow). B: Prostate MRI with diffusion-weighted imaging showing the dominant lesion (broken arrow) in the right posterior peripheral zone, not extending to the apex. C: Axial CT showing an enterocutaneous fistula related to known Crohn’s disease and demonstrating the enteric passage of contrast media (arrowheads) through the anterior abdominal wall (a potential cause of the reactive lymphadenopathy). Inguinal LN biopsy was negative for cancer. The patient was subsequently treated with brachytherapy and is free of recurrence at 368 days after diagnosis.

Figure 5.

Two patients with PCa and biopsy-proven inguinal LN metastases presenting with unilateral inguinal lymphadenopathy. A,B: CT of a 90-year-old man with ISUP grade group 4 PCa treated with RT 11 years prior. PSA was 13.0 ng/mL at baseline, with a biochemical response, now rising at 22.3 ng/mL. A: CT showing a left inguinal LN measuring 2.0 × 1.6 cm. Note the fiducial marker (black arrowhead), Foley catheter (white arrowhead), and rectal invasion by the superior portion of a recurrent prostate tumor (dotted outline). B: At a lower level, a recurrent prostate tumor (dotted outline) is shown directly invading the left corpus spongiosum of the penis through the membranous urethra and lower rectum. C,D: PSMA PET/CT of an 83-year-old man with ISUP grade group 3 PCa treated 17 years prior with RP followed by salvage RT and multiple lines of systemic treatment, the tumor subsequently becoming castration-resistant, with a PSA of 1.5 ng/mL. C: Maximumintensity projection PSMA PET/CT image showing widespread radiotracer-avid bone metastases. D: Axial fused PSMA PET/CT shows new deep right inguinal LN (broken arrow), measuring 1.1 × 1.1 cm, with an SUVmax of 17.8.

Figure 6.

CT and FDG PET/CT of an 82-year-old man with ISUP grade group 1 PCa treated with RT six years prior. PSA was 11.7 ng/mL at baseline, with a biochemical response, now rising at 2.5 ng/mL. A: Contrast-enhanced axial CT showing an enlarged, centrally necrotic left inguinal LN (arrow) measuring 7.3 × 5.0 cm. B: Fused axial FDG PET/CT showing a radiotracer-avid inguinal LN (arrow) with an SUVmax of 15.1. There were no findings suspicious for recurrence or metastases. Biopsy confirmed liposarcoma, which was suspected to be related to prior RT.

Figure 7.

FDG PET/CT of a 73-year-old man with newly diagnosed ISUP grade group 3 PCa. PSA was 6.3 ng/mL at baseline. A: Maximum-intensity projection FDG PET/CT image showing numerous radiotracer-avid LNs with diffuse distribution. B–D: Fused axial FDG PET/CT scans showing widespread lymphadenopathy (arrows) involving the thoracic, retroperitoneal, pelvic, and bilateral inguinal nodal stations. D: Left deep inguinal LN (circle) measuring 2.9 × 2.6 cm, with an SUVmax of 4.6 was biopsied and was initially negative for malignancy. Additional biopsy of a retroperitoneal LN revealed angioimmunoblastic T-cell lymphoma.