Villous adenoma of the prostatic urethra.

Primary villous adenoma originating from the urinary tract is an infrequent entity. We present a rare case of villous adenoma arising from a prostatic urethra with no sign of malignant transformation. Villous adenoma should be considered as one of the differential diagnoses of urethral lesions, especially if it has similar magnetic resonance imaging features as its colonic counterpart. Due to its potential for malignant transformation, its complete resection is mandatory.

Introduction

Primary villous adenoma originating from the urinary tract is an extremely rare entity, with less than 30 cases of villous adenoma in the urinary tract reported in the English language literature.[1234] Amongst the reported cases, the most common site of this lesion is in the urinary bladder and urachus, followed by the urethra and prostate.[12345] The patient usually presents with painless hematuria.[135] We report a rare case of villous adenoma of the prostatic urethra who presented with gross painless hematuria.

Case History

A 69-year-old male presented with intermittent gross painless hematuria and lower urinary tract symptoms (LUTS) since the past four years. He had a history of right urolithiasis, and had successfully underwent medical expulsive therapy. Initial cystoscopy done four years ago showed benign prostatic hypertrophy (BPH). No urethral lesion was noted at that time. He was started on alfuzosin and his LUTS was well controlled with the medication. However, for the past two months, there was an increasing frequency of episodes of gross painless hematuria. A repeat flexible cystoscopy was performed and a sessile villiform tumor was found in the prostatic urethra at the level of verumontanum, with minimal contact bleeding. However, we were unable to clearly visualize or navigate beyond the lesion. Urethral malignancy was suspected. He underwent magnetic resonance imaging (MRI) of the pelvis to assess the local extent of this urethral tumor. MRI shows a lobulated pedunculated lesion within the prostatic urethra, measuring approximately 0.8 × 0.8 × 0.7 cm. It was hypointense on T1WI and hyperintense on T2WI, with mildly heterogeneous enhancement on post gadolinium study [Figure 1]. A layer of T2 hyperintensity was seen surrounding the lesion on T2WI, which was possibly due to a mucin coating. A linear flow void signal was also seen within the stalk of the lesion on T2WI, representing a central vascular stalk [Figure 2]. There was no tumor extension into the prostate gland or any suspicious pelvic lymphadenopathy. The prostate gland was mildly enlarged (volume 29 ml) with MRI findings consistent with BPH.

Figure 1

(a) coronal and (b) axial T1-weighted fat-saturated post-contrast MRI images showing heterogeneously enhancing lobulated pedunculated lesion (black arrows) within the prostatic urethra with associated benign prostatic hyperplasia

Figure 2

Axial T2-weighted MR image showing layer of hyperintensity surrounding the lesion (white arrows), possibly representing mucin coating. Linear flow void (grey arrowhead) at the center of the lesion, representing a central vascular stalk

Transurethral resection of the tumor was carried out. Histopathology result showed tumor tissues arranged in villiform finger-like projections with a central fibrovascular core. These villi were lined by pseudostratified columnar epithelium, featuring elongated, hyperchromatic nuclei with preserved cellular polarity and apical mucin [Figure 3]. Von Brunn nests, cystitis cystica and cystitis glandularis were seen within the adjacent tissue. No malignant cells were seen. A diagnosis of villous adenoma of the prostatic urethra was made.

Figure 3

(a) section showing multiple fragments of tumour tissue arranged in villiform finger-like projections with central fibrovascular cores (H&E, 12.5x); (b) an enlarged rectangular area of 3a showing that these villi were lined by pseudostratified columnar epithelium, featuring elongated, hyperchromatic nuclei with preserved cellular polarity and apical mucin. Adjacent tissue was lined by benign stratified columnar urothelium exhibiting 5 to 7 layers of urothelial cells with overlying umbrella cells (H&E, 100x)

On follow up 3 weeks post-surgery, the patient's gross hematuria had completely resolved.

Discussion

The occurrence of a urethral tumor is sporadic.[6] The majority of adult male urethral tumors are malignant and most frequently seen in the bulbomembranous part (60%), followed by penile urethra (30%) and prostatic urethra (10%).[67] The most common histological type of urethral tumor is squamous cell carcinoma.[67]

Primary villous adenoma originating from the urinary tract is an extremely rare benign urethral tumor. There are two theories regarding the pathogenesis of the origin of this entity. Embryologically, the cloaca is divided into ventral and dorsal components by urorectal septum, which subsequently turns into urogenital tract and anorectum. The remaining cloaca rest within the urogenital tract is believed to proliferate into a glandular neoplasm.[458] Another theory suggests that chronic irritation/inflammation triggers the metaplasia-dysplasia response.[45] The present case favors the latter theory as there were concomitant findings of cystitis cystica and cystitis glandularis.

The cystoscopy examination is the first line of investigation. Apart from scope evaluation, MRI also plays a role in diagnosing urethral lesions. In imaging of urethral lesions, the MRI findings are often non-specific.[1] One might not be able to identify the usual “vegetating” shape of villous tumor from the MR image because the lesion is usually small. However, MRI findings such as the presence of T2 hyperintense mucin coating surrounding the tumor and central vascular stalk, which are frequently seen in villous gastrointestinal tumours,[910] increase the likelihood of the lesion being a villous adenoma.

It is essential to identify urinary tract villous adenoma due to its associated malignant potential.[123458] Complete resection of the villous adenoma is mandatory.[235] Histopathological evaluation confirms the diagnosis.[12] In the case series by Cheng et al.,[3] there was no recurrence or invasive adenocarcinoma in any patient with isolated villous adenoma of urinary tract during a mean follow-up period of 9.9 years.[3] The patient has been advised to follow up at 6-months post-operative for clinical evaluation; followed by an annual follow up with a local general practitioner for review of symptoms and a routine urinalysis.

Declaration of patient consent

The authors certify that appropriate patient consent was obtained.

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Conflicts of interest

There are no conflicts of interest.