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. Author manuscript; available in PMC: 2018 Jan 1.
Published in final edited form as: Semin Radiat Oncol. 2016 Aug 31;27(1):21–33. doi: 10.1016/j.semradonc.2016.08.008

Figure 2.

Figure 2

MRI Anatomy of Apex (note that the blue hashed lines represent the prostatic boundaries). (A–D): classic configuration with concave levator ani becoming convex below the apex, pinching in on the external sphincter. Note the thickening of the anterior rectal wall; the rectourethralis (RU) muscle extends from the rectum to the GUD, maintaining the rectal angle toward the anus below the prostate. (E–F) concave levator ani extending down an elongate GUD. (F) is a full cm below the apex and the levator has not pinched in as in (C). In (G–H), the levator pinches in but there is still definite prostate. Recognition of light PZ usually clarifies the apex extent. The clearest apex definition is on coronal T2. Legend: LA=levator ani, P=prostate, R=rectum, ES=external sphincter, GUD=genitourinary diaphragm, RU=rectourethralis muscle.