Objectives: To reclassify midline cysts (MLCs) of the prostate according using the results from transrectal ultrasonography (TRUS)-guided opacification and dye injection.
Patients and methods: Eighty-six patients (mean age 60.9 years) who had MLCs detected in the pelvis by TRUS were investigated. In all patients the size of the MLC was measured and they had transperineal aspiration under TRUS guidance. After aspiration of the MLC a mixture of water-soluble contrast medium and indigo carmine dye was injected to check for communication with the urethra or seminal tract by endoscopic and pelvic X-ray examination.
Results: We classified MLCs into four categories: (i) type 1 (nine cases), MLC with no communication into the urethra (traditional prostatic utricle cyst); (ii) type 2a (60 cases), MLC with communication into the urethra (cystic dilatation of the prostatic utricle, CDU); (iii) type 2b (14 cases), CDU which communicated with the seminal tract; (iv) type 3 (three cases), cystic dilation of the ejaculatory duct. The location, shape and volume of the MLC, and the prostate-specific antigen level of MLC fluid, did not influence the classification.
Conclusions: The most common type of MLC was CDU. A new classification that depends on the communication with the urethra or seminal tract is proposed.