Role of Diffusion-Weighted Magnetic Resonance Imaging (DWMRI) in Assessment of Primary Penile Tumor Characteristics and Its Correlations With Inguinal Lymph Node Metastasis: A Prospective Study.

Background: Penile cancer is a rare malignancy. The extent of lymph node (LN) metastasis is the most important prognostic factor in penile cancer. However, preoperative prediction of LN involvement in clinically non-palpable LN is still a challenge. In absence of a reliable biomarker, attempts are being made to validate imaging characteristics as a predictive tool. The aim of the present study is to assess the primary penile tumor characteristics with diffusion-weighted magnetic resonance imaging (DWMRI) and its correlations with inguinal LN status and tumor positivity in LN dissection specimen within normal sized LNs.

Methods: Twenty-six patients with carcinoma penis underwent DWMRI of penis and pelvis. The apparent diffusion coefficient (ADC) values of primary tumor were compared with histological characteristics. Inclusion criteria encompassed all cases of clinically non-palpable inguinal LN and normal sized LN on imaging. All palpable inguinal nodes with pelvic lymphadenopathies were excluded from this study.

Results: The primary tumor ADC ranged from 0.65 × 10 - 1.2 × 10 mm/s (mean: 0.87 × 10 ± 0.11 × 10 mm/s). In pT1 and pT3 tumors, mean ADC values were 0.86 × 10 ± 0.10 × 10 and 0.81 × 10 ± 0.09 × 10 mm/s, respectively. The mean ADC values for grade 1, grade 2 and grade 3 were 0.89 × 10, 0.82 × 10 and 0.80 × 10 mm/s, respectively. The ADC value of < 0.95 × 10 mm/s was positively correlated with pathological LN presence within normal sized LN. With mean ADC value of 0.87 × 10 ± 0.11 × 10 mm/s, sensitivity and positive predictive values for primary penile cancer were 100% and 84.61%, respectively. The mean ADC value for higher-grade and -stage tumor was low. The sensitivity and specificity of predicting LN metastasis by DWMRI were 87.22% and 80.90%, respectively.

Conclusion: ADC value of primary tumor can help in prediction of LN metastasis in carcinoma penis with clinically and radiologically normal groin.