Surgical anatomy of the puboprostatic complex with special reference to radical perineal prostatectomy

Authors


Th. F. Wimpissinger, MD, Department of Urology, Rudolfstiftung Hospital, Juchgasse 25, A−1030, Vienna, Austria.
e-mail: florian.wimpissinger@gmx.at

Abstract

We are always interested in developing an understanding of anatomical relationships, particularly as this can often make surgery more reliable for patients; the classic anatomical studies of Walsh and Donker are remembered by everyone. Here, the authors from Vienna investigate the retropubic space and the attachments of the prostate and urethra to aid the performance of radical perineal prostatectomy.

Authors from London describe their criteria based on clinical experience, for performing bone scans in patients with prostate cancer. Their proposals are somewhat more exclusive than some of the suggestions made previously but it is worth considering the authors’ views and seeing whether they might be valid and important guidelines for the future.

On the subject of bone metabolism in prostate cancer, authors from the UK suggest that there is a high incidence of osteoporosis in patients with advanced prostate cancer before hormonal manipulation, and that patients requiring such treatment should have densitometry before starting treatment.

OBJECTIVE

To investigate the retropubic space and attachments of the prostate and urethra, with special reference to radical perineal prostatectomy.

MATERIALS AND METHODS

Anatomical relationships were assessed intraoperatively in 60 patients, and in five cadavers after preparing the dorsal vein complex with coloured latex. Cross-sections of the area of interest were evaluated by microscopy.

RESULTS

The puboprostatic (pubovesical) ligaments could be clearly distinguished from the median part of the puboprostatic complex continuous with the urethral suspensory mechanism. The dorsal vein complex is integrated into this fibromuscular attachment of the prostate and male urethra. During the perineal approach, dissection in this region follows the so-called avascular plane.

CONCLUSION

With this new insight into the anatomical relationships the nomenclature derived from radical retropubic prostatectomy could be mirrored. In radical perineal prostatectomy, both the urethral suspensory mechanism and the dorsal vein complex can be preserved.

INTRODUCTION

The retropubic space, particularly the puboprostatic ligaments, have become increasingly important over the last few years, with the focus on preserving urinary continence after radical retropubic prostatectomy. Zacharin [1] was the first to describe a ‘suspensory mechanism of the urethra’ in the female anatomy. Preserving these structures has been reported to be important in urinary continence after radical retropubic prostatectomy [2–4]. We postulated that preserving these structures has always been a natural anatomical result of the perineal approach, which was described as early as 1869 [5] and became popular after Young's detailed descriptions [6]. Furthermore, dissection in this region carries a serious risk of bleeding, which can be reduced by understanding the anatomy of the dorsal vein complex and its relationship to surrounding tissue. Curing the patient of his cancer is the purpose of the procedure and must always be considered when assessing new techniques and methods of dissection in any setting, including the anatomy laboratory. In the present study we focused on this crucial area from the perspective of radical perineal prostatectomy. The anatomical details of this procedure are rather ambiguous, as every surgeon is apt to use a different nomenclature.

MATERIALS AND METHODS

The surgical anatomy of the prostate was studied from three different aspects; first, in 60 consecutive radical perineal prostatectomies performed by one surgeon (W.S.) over a year; second, an anatomical dissection of two fresh and three fixed male pelves; and third, a microscopic investigation of two anatomical specimens. For the second method, to assess the retropubic structures in detail, the dorsal vein complex was injected with coloured latex via the dorsal vein of the penis. This facilitated the clear identification of the venous network and its relationship to ligaments and the prostate. Cooperation between the surgeon and physician working in the anatomy laboratory, with discussions in the operating theatre, were essential for describing the anatomical details. Microscopically, the structures of the puboprostatic complex were assessed using haematoxylin and eosin staining and immunohistochemical staining for smooth muscle actin, to identify the connective tissue, muscle fibres and vascular structures.

RESULTS

The findings from the three studies taken together showed that the ‘puboprostatic complex’ essentially consists of the following elements.

(i) Most superiorly the puboprostatic ligaments attach the pubovesical junction to the pubic symphysis in a horizontal plane (Fig. 1). These ligaments insert at the base of the prostate and are pyramidal, extending laterally into the endopelvic fascia which covers the lateral pelvic muscles (levator ani, internal obturator). They appear as a dense medial part of the endopelvic fascia. Most superiorly they are in continuation with muscle fibres of the bladder wall, constituting the so-called ‘detrusor apron’[7]. These ligaments may be referred to as the posterior pubourethral ligament, according to Steiner's concept of the urethral suspensory mechanism [8].

Figure 1.

Puboprostatic ligaments from the retropubic approach: BW, Bladder wall; Sy pubic symphysis; PB, puboprostatic ligaments; EPF, endopelvic fascia.

(ii) The dorsal vein complex and Santorini plexus; the dorsal vein of the penis enters the retropubic space through Buck's fascia underneath the pubic arch, and drains into a venous network lying below the level of the aforementioned puboprostatic ligaments, and behind the pubic symphysis. They lie in retropubic fat laterally and are separated from the prostate by fibromuscular and soft connective tissue.

(iii) Fibromuscular and soft connective tissue attach the prostate to the pubic arch in the median plane inferior to the puboprostatic ligaments (Fig. 2). This attachment is part of the so-called intermediate pubourethral ligament [8]. It inserts at the anterior commissure of the prostate, the isthmus prostatae. This tissue partly inserts in the walls of veins, partly integrating them into the suspension mechanism. At the distal margin of this structure are the urethra and the anterior pubourethral ligament.

Figure 2.

Puboprostatic area 2 mm left of the mid-sagittal plane: B, bladder; P, prostate; Sy, pubic symphysis; V, puboprostatic venous complex; 1, left puboprostatic ligament; 2, retropubic fat; 3, pubourethral ligament; 4 (arrow), plane of dissection in radical perineal prostatectomy.

Microscopy showed that the so-called ‘suspensory mechanism’ of the urethra consists of both soft connective tissue with retropubic fat and a substantial quantity of smooth and striated muscle cells (Fig. 3). The periprostatic veins appear more like sinuses integrated into this dense fibromuscular stroma, together with sporadic small arteries.

Figure 3.

Histological section, retropubic space, sagittal: wide, thin-walled vascular channels (V) embedded in fibrous tissue intermingled with fat and scarce muscular bundles. P, prostate; PS, pubic symphysis; U, urethra; A, small artery (immunohistochemical staining for smooth muscle actin, visualized with diaminobenzidine, × 4).

DISCUSSION

From these results we propose the following pathway for radical perineal prostatectomy, starting at the point of preserving the urethral stump. After disconnecting the proximal urethra at the apex of the prostate, the anterior urethral wall is in continuation with the anterior and intermediate pubourethral ligaments. Dissection follows the ventral aspect of the apex and the anterior commissure along the capsule of the gland. Laterally the space between the anterior aspect of the prostate and the pubic symphysis can be bluntly dissected with the surgeon's finger. Fibromuscular tissue between the dorsal vein complex and the prostate is dissected in the midline, between the pubic symphysis and the anterior commissure of the prostate, usually without severing any veins. This area can be referred to as the ‘avascular plane’[7]. Dissection is either with scissors or with the harmonic scalpel. The endpoint of this pathway is the puboprostatic ligaments, which stand like a wall at the pubovesical junction. They are dissected sharply, allowing for a free bladder neck that is necessary to mobilize the bladder for anastomosis. Taken together, these structures can be viewed as T-shaped (Fig. 4), i.e. in the horizontal plane the puboprostatic ligaments, and in the vertical plane the intermediate pubourethral ligament (i.e. ‘median complex’).

Figure 4.

Prostate, position of the puboprostatic complex. Blue, puboprostatic ligaments at the prostatovesical junction; green, intermediate pubourethral ligament at the anterior commissure of the prostate; red, urethral stump.

The first description of a ‘plexus venosus vesicoprostaticus’ was provided by Giovanni Domenico Santorini in 1724 [9,10]. Since then several precise descriptions of the anatomy of the dorsal vein complex and its variations with special regard to surgical technique have been proposed [11–13]. It is usually hard to study veins in the operating theatre or the anatomy laboratory. We partly adopted the method of Beneventi and Noback [11], injecting the veins to study the surrounding structures. The additional injection of coloured latex provided excellent anatomical images.

As early as in 1905, Young [6,14] suggested that intact puboprostatic ligaments support the bladder neck and promote urinary continence after radical perineal prostatectomy. The role of a urethral suspensory mechanism for urinary continence after radical retropubic prostatectomy was investigated by others [2–4]. Our findings from the perineal approach concur with the concept of a urethral suspensory mechanism. Thus, the anatomy of the anterior suspensory complex may be viewed as a structure composed of three parts, as described by Steiner [8], i.e. anterior (membranous urethra), intermediate (anterior commissure of prostate) and posterior (pubovesical junction) pubourethral ligaments.

The structures being dissected at the ventral aspect of the prostate (often falsely referred to as puboprostatic ligaments [6]) are a distinct layer of connective tissue attaching the prostate to the pubic symphysis at the level of the dorsal vein complex. In 1979, McNeal [15] gave a clear description of this ‘anterior fibromuscular stroma’. Dissection really follows an ‘avascular plane’[7] during the perineal approach. Macroscopically, this is the intermediate pubourethral ligament [8].

In the present study we focused exclusively on the ‘ventral part’ of radical perineal prostatectomy. Obviously, the posterior tendon of the external urethral sphincter (the rectourethralis muscle and posterior median raphe) is totally dissected during the perineal approach on the way to Denonvillier's fascia. The anterior reflection of these structures is the anterior pubourethral ligament [8], the distal portion of the pubourethral suspensory mechanism. Leaving this pubourethral suspensory mechanism intact and constructing a very precise vesicourethral anastomosis under direct vision seems to compensate for this drawback of the procedure for urinary continence after surgery.

That the puboprostatic ligaments insert at the base of the prostate was further confirmed by Myers et al.[16], who even suggested that they should be termed the ‘pubovesical ligaments’, as seen on MRI. However, most fibres attach to the prostate (Figs 2 and 3), but in some individuals certain branches fix the bladder neck to the pubic symphysis and make it difficult to achieve sufficient mobility to create a tension-free anastomosis in radical perineal prostatectomy. These insertions of bladder wall muscle fibres have lately been termed the ‘detrusor apron’[7].

Microscopic studies confirmed the concept of a connective tissue suspension mechanism, as noted previously [2,17]. We found the veins of the Santorini plexus to be integrated into this fibromuscular tissue, giving them an appearance of sinuses rather than veins. Radical perineal prostatectomy has been shown to be oncologically safe [18–20]. Our technique of dissection at the ventral aspect of the prostate was also safe oncologically and allows for total excision of the gland and its capsule.

In conclusion, for radical perineal prostatectomy, we show that both the dorsal vein complex and the urethral suspension mechanism can be preserved, leaving the attachment of the sphincteric urethra intact. Apart from the puboprostatic ligaments there is a distinct fibromuscular attachment of the prostate and male urethra to the pubic symphysis, incorporating the veins of the dorsal vein complex. Accordingly, we would propose adding the term ‘puboprostatic complex’ to Young's description of ‘… leaving the puboprostatic ligaments intact.’ Thus radical perineal prostatectomy has always been a continence-preserving procedure.

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