title: Functional anatomy of the prostate: implications for treatment planning.
abstract: OBJECTIVE
  To summarize the functional anatomy relevant to prostate cancer treatment planning.
  
  
  METHODS
  Coronal, axial, and sagittal T2 magnetic resonance imaging (MRI) and MRI angiography were fused by mutual information and registered with computed tomography (CT) scan data sets to improve definition of zonal anatomy of the prostate and critical adjacent structures.
  
  
  RESULTS
  The three major prostate zones (inner, outer, and anterior fibromuscular) are visible by T2 MRI imaging. The bladder, bladder neck, and internal (preprostatic) sphincter are a continuous muscular structure and clear definition of the preprostatic sphincter is difficult by MRI. Transition zone hypertrophy may efface the bladder neck and internal sphincter. The external "lower" sphincter is clearly visible by T2 MRI with wide variations in length. The critical erectile structures are the internal pudendal artery (defined by MRI angiogram or T2 MRI), corpus cavernosum, and neurovascular bundle. The neurovascular bundle is visible along the posterior lateral surface of the prostate on CT and MRI, but its terminal branches (cavernosal nerves) are not visible and must be defined by their relationship to the urethra within the genitourinary diaphragm. Visualization of the ejaculatory ducts within the prostate is possible on sagittal MRI. The anatomy of the prostate-rectum interface is clarified by MRI, as is the potentially important distinction of rectal muscle and rectal mucosa.
  
  
  CONCLUSIONS
  Improved understanding of functional anatomy and imaging of the prostate and critical adjacent structures will improve prostate radiation therapy by improvement of dose and toxicity correlation, limitation of dose to critical structures, and potential improvement in post therapy quality of life.
authors.affiliation: Department of Radiation Oncology, Providence Hospital, Southfield, MI, USA. mclaughb@umich.edu
authors.forename: Patrick W
authors.initials: PW
authors.lastname: McLaughlin
authors.forename: Sara
authors.initials: S
authors.lastname: Troyer
authors.forename: Sally
authors.initials: S
authors.lastname: Berri
authors.forename: Vrinda
authors.initials: V
authors.lastname: Narayana
authors.forename: Amichay
authors.initials: A
authors.lastname: Meirowitz
authors.forename: Peter L
authors.initials: PL
authors.lastname: Roberson
authors.forename: James
authors.initials: J
authors.lastname: Montie
mesh_terms: D004542:Ejaculation; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D017773:Pelvic Floor / Q000033:anatomy & histology; D010388:Pelvis / Q000033:anatomy & histology; D010410:Penile Erection; D010413:Penis / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000294:innervation; D010502:Perineum / Q000033:anatomy & histology; D011467:Prostate / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D012007:Rectum / Q000033:anatomy & histology; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography; D014521:Urethra / Q000033:anatomy & histology; D001743:Urinary Bladder / Q000033:anatomy & histology