Urethral Sphincter

Anatomy

The prostate sphincter complex - usually referred to as the external sphincter - is an important landmark in endourological diagnostics and surgery. It is of utmost importance for the preservation of continence after endourological surgery. TUR-P and urethrotomy are the most common endourological procedures where the external sphincter and its anatomy have to be considered and preserved.

The knowledge on the anatomy of the external sphincter has increased over the years. The image of a plane muscular layer distal to the prostate, as often described in textbooks on pelvic anatomy, is not correct (O Fig. 8.1).

The prostate sphincter complex consists of different muscular aspects:

™ The striated sphincter itself, which is the relevant part of the complex in endourologi-cal surgery.

™ It has an omega-like shape (Q) with the »open side« pointing towards the rectum (illustrated in O Fig. 8.2b). The striated sphincter is a broad muscular loop on its ventral parts with an extension over the ventral aspects of the prostate [1, 2] (O Figs. 8.2a, c, 8.3). ™ Heterogenous prostate shapes [2] (e.g. donut vs. croissant shape) result in diffe-

Prostate Smooth Muscle
□ Fig. 8.1. Incorrect image of the external sphincter. The sphincter is often described as a muscular disc distal to the prostate.
External Urethral Sphincter

□ Fig. 8.2A-C. Illustration of the male striated urethral sphincter (reconstruction of the embryological situation). The sphincter extends over the ventral aspects of the prostate (A, C, left lateral view) and has an omega-like shape (B, dorsal view). Red: sphincter, white: bladder neck and urethra, yellow: prostate. From [1]

External Striated Urethral Sphincter

□ Fig. 8.3. Illustration of the male striated urethral sphincter (sagittal view). The sphincter (8) extends on the ventral aspects of the prostate. Note that in the sagittal view no sphincter but a midline fibrous raphe (21) is present in the dorsal aspects of the periurethral region distally from the apex of the prostate (2). From [4] (by permission of Mayo Foundation for Medical Education and Research. All rights reserved)

rent sphincter anatomies (□ Fig. 8.4). One has to keep this in mind, for example, when doing the resection of ventral apical aspects during TUR-P.

™ The pubourethral aspects of the sphincter muscle.

™ The urethral smooth muscles (circular and longitudinal muscular fibres).

Innervation

The innervation of the prostate sphincter complex has different origins: ™ Pudendal nerve: somatic ™ Branches of the sacral plexus: somatic ™ Cavernous nerves (derived from hypogastric nerve and pelvic splanchnic nerve), auto-nomic: innervation of the urethral smooth muscles suspected.

Prostate Apex

□ Fig. 8.4A-D. Different prostate shapes and the consecutive heterogeneous relation of the apex and the external sphincter. The shape of the prostate can occur as a crescent (A) or a donut (C). In the sagittal view (B, D) the relation of the prostate (black) and the sphincter area (red) with different prostate shapes is illustrated. A, C from [4]; B, D from [5] (by permission of Mayo Foundation for Medical Education and Research. All rights reserved)

□ Fig. 8.4A-D. Different prostate shapes and the consecutive heterogeneous relation of the apex and the external sphincter. The shape of the prostate can occur as a crescent (A) or a donut (C). In the sagittal view (B, D) the relation of the prostate (black) and the sphincter area (red) with different prostate shapes is illustrated. A, C from [4]; B, D from [5] (by permission of Mayo Foundation for Medical Education and Research. All rights reserved)

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