Urogenital ImagingCarcinoma, male urethra
a rare malignancy, only approximately 600 cases have been reported in the world literature. Although significant aetiological factors have not been identified, chronic
inflammation may play a role since many patients give a history of prior venereal disease, urethritis, or urethral stricture. An increased incidence has also been reported with smoking or occupational exposure to known carcinogens. Symptoms such as urethral bleeding and a weak urinary stream, are nonspecific and are often attributed to
benign stricture disease rather than to malignancy. As a result there is often a delay, 5 months on average, before the diagnosis is made. Transurethral or needle
biopsy is required for definitive diagnosis. In the majority of cases (78%) the cancer is a squamous cell
carcinoma. Other types include transitional cell (15%), adenocarcinoma (6%), and undifferentiated carcinomas (1%). Initial spread is by direct extension to adjacent structures via the
vascular spaces of the corpus spongiosum and the periurethral tissue.
Carcinoma of the bulbomembranous
urethra often extends to the urogenital
diaphragm. Haematogenous spread is uncommon except in advanced cases.
Metastases to regional lymph nodes occur by lymphatic embolization. The lymph node chain involved is dictated by the location of the carcinoma. As discussed earlier, lymphatics from the anterior urethra drain into the superficial and deep inguinal nodes and occasionally to the external iliac nodes. Lymphatics from the posterior urethra, however, drain into the external iliac, obturator and internal iliac nodes. When the disease involves the distal part of the penis, the extent of local involvement can be determined by careful inspection and by bimanual examination. Cancer in the bulbomembranous urethra, however, requires radiological evaluation. Carcinoma of the prostatic urethra is rare. The approach to staging is based on the location of the carcinoma, as is the treatment. Carcinoma of the distal urethra can be treated by resection, partial penectomy or total penectomy, depending on the extent of disease. Lesions in the bulbous urethra or more proximal lesions require extensive surgical resection (possibly including en bloc removal of the penis, urethra, prostate, bladder with overlying pubis, and pelvic lymph nodes) and an ileal diversion. Unfortunately, there are no reports of survival figures for the various forms of surgical treatment.
Imaging
Retrograde urethrography may show a filling defect (Fig.1). Although penile and urethral carcinomas are clinically separable entities in their early stages, once the lesions have infiltrated and deeper structures become involved, their MRI appearance is the same. On T1-weighted images, urethral or penile carcinoma demonstrates a signal intensity similar to or lower than that of the surrounding corporeal body. In T2-weighted images, tumours have a low signal intensity regardless of their histological type. Urethral tumours, especially when located in the glans penis, will be associated with extensive inflammatory reaction and often abscess formation. In those instances underlying inflammatory changes will influence the signal intensity of the involved region. Often on T1-weighted images, they may demonstrate medium or low signal intensity, and marked increase in signal intensity on T2-weighted image (Fig.2). The extent of the disease can accurately be evaluated. MRI has a limited role in the evaluation of disease extent for carcinoma located in the glans penis. However, when the tumour extends into the radix penis, clinical examination becomes limited and the value of MRI increases. The tumour extension is identified by the demonstration of the low-signal-intensity tumour within corporeal tissue. On the T2-weighted image, involvement and tumour extension into the septum of the corpora cavernosa or tunica albuginea can be demonst decreased signal intensity. The tumour margins are usually ill-defined, and although the abnormality can be detected, the differentiation between primary and metastatic lesion cannot be made. Tumour extension and invasion of the tunica albuginea can be seen by the interruption of the low-signal-intensity tunica on T2-weighted images. When complicated with priapism, clinical diagnosis and the physical examination are very limited. The use of MRI in those cases can be helpful. The role of radiology in the evaluation of penile carcinoma was previously directed at the assessment of lymphadenopathy (using lymphangiography or CT) and the detection of distant metastases (chest radiography, CT and liver and bone scintigraphy). Local staging of the disease, however, was not attempted before the introduction of MRI. The ability of MRI to assess local tumour extent may impact on decisions as to the therapeutic approach. MRI is applicable, however, only to larger lesions and especially lesions located in the radix penis where clinical examination is limited. However, although local tumour extension can be accurately determined from MR images, it should be emphasized that MR imaging is not specific for tumour diagnosis, nor is it yet known whether urethral carcinoma can be differentiated from diffuse fibrous, inflammatory or postsurgical changes.
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