Multiparametric Magnetic Resonance Imaging of Penile Cancer: A Pictorial Review

Abstract

The role of multiparametric magnetic resonance imaging (mpMRI) in assessing penile cancer is not well defined. However, this modality may be successfully applied for preoperative staging and patient selection; postoperative local and regional surveillance; and assessments of treatment response after oncological therapies. Previous studies have been mostly limited to a few small series evaluating the accuracy of MRI for the preoperative staging of penile cancer. This review discusses the principles of non-erectile mpMRI, including functional techniques and their applications in evaluating the male genital region, along with clinical protocols and technical considerations. The latest clinical classifications and guidelines are reviewed, focusing on imaging recommendations and discussing potential gaps and disadvantages. The development of functional MRI techniques and the extraction of quantitative parameters from these sequences enables the noninvasive assessment of phenotypic and genotypic tumor characteristics. The applications of advanced techniques in penile MRI are yet to be defined. There is a need for prospective trials and feasible multicenter trials due to the rarity of the disease, highlighting the importance of minimum technical requirements for MRI protocols, particularly image resolution, and finally determining the role of mpMRI in the assessment of penile cancer.

Keywords: MRI; diffusion-weighted imaging; dynamic contrast-enhanced MRI; guidelines; multiparametric magnetic resonance imaging; penile cancer; staging.

Figure 1

Recommended coverage of the anatomical area by morphological and functional sequences in penile MRI (DWI—diffusion-weighted imaging, DCE-MRI—dynamic contrast-enhanced MRI, FOV—field of view).

Figure 2

Stages of penile cancer according to the eighth edition of the Union for International Cancer Control (UICC)/American Joint Committee on Cancer (AJCC) TNM classification. Ta, noninvasive localized squamous cell carcinoma. T1, invasion of subepithelial connective tissue. T2, invasion of corpus spongiosum with or without invasion of urethra. T3, invasion of corpus cavernosum with or without invasion of urethra. T4, invasion of adjacent structures.

Figure 3

MpMRI findings of superficial (A–D) and deeply invasive (E–H) T2 penile cancer. The superficial tumor is difficult to outline on T2-weighted imaging (A); however, the high b-value DWI increases the conspicuity of the lesion, showing high signal intensity in tumor tissue (B, arrows). The tumor has a moderately low ADC (950 μmm²/s) (C). Subsequent surgery presented a good correlation between tumor thickness on mpMRI (C) and histopathology. The contrast-enhanced T1-weighted imaging shows tumor infiltration into the dorsal part of the glans (D, arrows). The lower row (E–H) shows a deeply invasive tumor in the glans (E—T2-weighted imaging, dashed line), located close but not infiltrating into the adjacent tunica albuginea (E, arrowheads). The conspicuity of the tumor and its boundaries increase on high b-value DWI (F, arrows), ADC (G) and contrast-enhanced T1-weighted imaging (H, arrow).

Figure 4

Sagittal T2-weighted imaging (A), high b-value DWI (B) and ADC (C) showing a large T3 penile cancer (arrows). The tumor infiltrates the corpus spongiosum and cavernosum and there is massive infiltration in the penile urethra. The small, deeply located tumor satellite in the corpus cavernosum is shown (A, arrowhead). This finding is crucial for surgery planning since the satellite defines the proximal tumor extent and is almost impossible to detect clinically because of its small size. The tumor satellite has a high signal intensity in DWI (D, arrow). The tumor has high vascular permeability, as shown on the wash-in (K^trans) (E, arrows) and washout (k_ep) (F) perfusion maps and contrast-enhanced T1-weighted imaging (G, arrows). A large inguinal lymph node metastasis is also shown (G, arrowhead). Photomicrograph of a whole mount hematoxylin and eosin-stained section shows a large tumor in the corpus spongiosum, cavernosum, and urethra (H, arrows). Photomicrograph of histologic specimen shows infiltration of basaloid squamous cell carcinoma (I, magnification ×10).

Figure 5

MRI findings of large T1 penile cancer. T2-weighted imaging (A, asterisk) and high b-value DWI (B, arrows) show a large prepuce tumor. The tumor lies close to but does not infiltrate the glans, with a visible fluid layer between the glans surface and tumor (A, arrows, g—glans, u—urethra). The ADC map displays low diffusion in the tumor (C). DCE-MRI (D) shows high permeability in the tumor with subsequent washout (D, white curve), in contrast to homogenously enhancing the glans with lower vascular permeability and no washout (D, green curve). The contrast-enhanced T1-weighted imaging shows reduced contrast enhancement in the tumor compared to surrounding structures, due to washout (E, asterisk).

Figure 6

MpMRI findings of local and regional nodal recurrence. A fusion overlay of high b-value DWI and T2-weighted imaging shows local recurrence after partial penectomy (A, arrows). The findings are obvious in contrast-enhanced T1-weighted imaging (B, arrow) and DCE-MRI (C,D). There is rapid enhancement on the wash-in (K^trans) perfusion map within the tumor (C, circle) and some washout on the perfusion curve (D). T1-weighted imaging shows extensive contrast enhancement in the postsurgical bed after ILND, more than can be expected from postsurgical scarring and fibrosis (E, arrows). DWI and ADC map show suspicious low diffusion within the enhancing tissue, consistent with tumor infiltration (F,G, arrows). Histopathological examination confirmed both local and regional nodal recurrence from penile cancer.

Figure 7

Evaluation of the treatment response on penile MRI. The upper row (A–D) shows pretreatment findings of large penile cancer on T2-weighted imaging (A, dashed line), high b-value DWI (B, arrows), and ADC map (C). Large inguinal lymph node metastases are also shown (D—T2-weighted imaging, arrows). Note the pathological signal in the bone marrow, secondary to known chronic myelogenous leukemia (D, asterisk). The lower row (E–H) shows the posttreatment findings after the start of chemotherapy. The tumor has a stable volume; however, high signal intensity on T2-weighted imaging has appeared since the pretreatment scan, consistent with necrosis and the treatment response (E, dashed line). The ADC is slightly higher, which is also consistent with the response (G). There is some treatment response in the inguinal lymph nodes with the slight shrinkage of solid tumor tissue and increased necrosis on T2-weighted imaging (H, asterisk).

Figure 8

MRI findings of pseudoepitheliomatous hyperplasia with inflammation. T2-weighted imaging shows an exophytic lesion along the inner layer of the prepuce (A, arrows, g—glans, cc—corpus cavernosum). High b-value DWI (B) and ADC map (C, circle) show heterogenous yet predominantly high diffusion in the lesion (ADC > 1300 μmm²/s). Contrast-enhanced T1-weighted imaging displays an exophytic lesion with a papillomatous surface along the inner prepuce and glans (D, arrows). The lesion is vascularized; however, the permeability rate is very low, as shown on the wash-in (K^trans) perfusion map (E, arrow). Photomicrographs of histologic specimens display pseudoepitheliomatous hyperplasia with inflammation (F—magnification × 2, G—magnification × 4, H—magnification × 10).

Figure 9

MRI findings of penile metastasis originating from rectal cancer. The upper row shows low, locally advanced rectal cancer (arrows) (A—T2-weighted imaging, B—DWI, C—ADC). The lower row (D–F) shows penile metastasis located in the posterior part of the left corpus cavernosum. The lesion can be easily overlooked on T2-weighted imaging (D, circle); however, high b-value DWI (E, arrow) and ADC (F, arrow) increase the conspicuity of the tumor.

Figure 10

MpMRI findings of urethral cancer. T2-weighted imaging (A, arrows) and high b-value DWI (B, circle) show a small lesion along the spongy urethra. The lesion has low diffusion on the ADC map (C, arrow), and displays an enhancement pattern typical for malignant tumors in contrast-enhanced T1-weighted imaging (D, circle) and DCE-MRI (E,F, arrows). The wash-in (K^trans) perfusion map shows early enhancement in the lesion, but in a lesser grade than the adjacent, rich vascularized corpus spongiosum (E, arrow). The k_ep perfusion map displays subsequent washout in the tumor (F, arrow). The histological evaluation confirmed urethral squamous cell carcinoma.

Figure 11

MpMRI findings of penile malignant melanoma. A large, cell-dense tumor in the navicular fossa of spongy urethra is detected in T2-weighted imaging (A, arrows), high b-value DWI (B, arrow), and ADC (C). The primary tumor (D, arrow) and inguinal nodal metastasis (E, arrow) are hyperdense on T1-weighted imaging because of the paramagnetic effect of melanin and/or blood products. The tumor is richly vascularized, as shown in the wash-in (K^trans) perfusion map (F, circle).

Figure 12

T2-weighted imaging showing a large exophytic tumor located just inferior to the glans and consistent with a condyloma (A, arrow, g—glans, u—urethra, t—testicle). The high b-value DWI (B, t—tumor, cc—corpus cavernosum, asterisk—testicle) and ADC (C) display predominantly high diffusion in the tumor (ADC > 1000 μmm²/s). The tumor has a cauliflower-like appearance in DCE-MRI (D—wash-in (K^trans) map, E—washout (k_ep) map) and contrast-enhanced T1-weighted imaging (F). The diffusion is high; however, the papillomatous surface shows a high vascular permeability, with subsequent washout (D–F, arrows, s—tumor stalk, u—urethra, g—glans, t—testicle). A photomacrograph of formalin-fixed specimen shows a large, cauliflower-like tumor, consistent with a condyloma (G). Photomicrograph of histologic specimen shows condyloma with development of well-differentiated squamous cell carcinoma (H, magnification × 2).

Figure 13

T2-weighted imaging (A, arrow) and high b-value DWI (B, arrow) show a well-demarcated lesion within the right part of the glans. The lesion has very low diffusion, and the ADC is lower than that expected from the tumor (ADC = 300 μmm²/s) (C). The lesion is not vascularized, as shown in the contrast-enhanced T1-weighted imaging (D, arrow) and wash-in (K^trans) perfusion map (E, dashed line). The findings are consistent with the penile abscess. The biopsy was performed to exclude underlying malignancy but was negative.