© 2004 Foundation for Promotion of Cancer Research
Anatomical Features of Periprostatic Tissue and its Surroundings: a Histological Analysis of 79 Radical Retropubic Prostatectomy Specimens
1 Department of Anatomic Pathology and 2 Department of Urology, Graduate School of Medical Science, Kyushu University, Fukuoka, 3 Department of Urology, University of Occupational and Environmental Health, School of Medicine and 4 Department of Urology and 5 Department of Pathology, National Kyushu Cancer Center, Fukuoka, Japan
For reprints and all correspondence: Keijiro Kiyoshima, Department of Anatomic Pathology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Japan. E-mail: kkiyo{at}surgpath.med.kyushu-u.ac.jp
Received March 21, 2004; accepted May 15, 2004
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Abstract |
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Background: A proper understanding of prostatic and periprostatic anatomy is essential for surgical procedures and pathological diagnosis; however, the detailed features have not been commonly investigated and completely understood.
Methods: Seventy-nine non-nerve-sparing radical prostatectomy specimens were microscopically investigated for Denonvilliers' fascia, lateral pelvic fascia, prostatic capsule, anterior fibromuscular stroma and the neurovascular bundle.
Results: At the lateral aspect, the lateral pelvic fascia and the prostatic capsule were separated by adipose tissue in 41 cases (52%), whereas they adhered in 38 cases (48%). In only 41 cases (52%), the neurovascular bundle existed locally at the postero-lateral region with definite ‘bundle’ formations. Denonvilliers' fascia and the prostatic capsule adhered tightly at the center of the posterior aspect in 77 cases (97%). A smooth transition from the prostatic capsule to the anterior fibromuscular stroma was observed in all cases. In 70 cases (89%), no prostatic capsule was independently recognized at the anterior aspect. In the remaining 9 cases (11%), the capsule was recognizable as distinct from the anterior fibromuscular stroma. In 67 cases (85%), the lateral pelvic fascia connected and fused with the anterior fibromuscular stroma, and covered the outermost regions of the lateral and anterior surfaces.
Conclusions: All the periprostatic structures are closely related and influence each other. The results support the rationale of anatomical radical prostatectomy, and should be taken into consideration for surgical procedures and pathological diagnosis.
Key Words: radical prostatectomy • Denonvilliers' fascia • lateral pelvic fascia • prostatic capsule • periprostatic structures
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INTRODUCTION |
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Radical prostatectomy is one of the primary curative procedures for clinically localized prostate cancer. Advances in the anatomical elucidation of the prostate and surgical techniques have contributed to accurate procedures of radical prostatectomy and excellent survival (1).
In Japan, the number of clinically localized prostate cancer cases has been increasing due to advances in the diagnostic methods and the spread of medical information about this disease among the masses. Recently, endoscopic surgeries have been considered to be safe procedures. However, urologists occasionally encounter intra-operative excessive bleeding, iatrogenic positive surgical margin and post-operative complications such as urinary incontinence and erectile dysfunction. Furthermore, with an increase in the number of specimens submitted for investigation, pathologists sometimes take time to properly evaluate the extent of cancer and its locations.
The number of investigations for the microscopic anatomy of the periprostatic tissue is limited (2–5); nevertheless, precise interpretations of the periprostatic anatomical features are critical for the accurate understanding of the disease status, surgical procedures and pathological evaluations as well. Therefore, we investigated non-nerve-sparing radical retropubic prostatectomy specimens to elucidate the accurate periprostatic anatomical features and their relationships to the prostate, and discuss the rationale and refinement of radical prostatectomy.
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SUBJECTS AND METHODS |
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Seventy-nine non-nerve-sparing procedure cases were selected from a series of 140 consecutive radical retropubic prostatectomies performed at the National Kyushu Cancer Center between May 1998 and May 2002. None of the selected cases received any pre-surgical treatment such as radiation or hormonal therapy. Before the operation, we informed each patient about the indications, contents and complications, including urinary incontinence and erectile dysfunction, and received written consent to be included in our program.
The submitted prostates were fixed in 10% neutral formalin, sectioned horizontally into layers of 4 mm thickness and embedded in paraffin. Further, sections with an average thickness of 3 µm were prepared, and then stained with hematoxylin–eosin.
We investigated all the sections, and then selected a few specimens per case where we could evaluate all aspects for analysis. The following anatomical features of the periprostatic tissue were analyzed in the selected specimens: Denonvilliers' fascia (DF), lateral pelvic fascia (LPF) and neurovascular bundle (NVB). In addition, some non-periprostatic structures such as the prostatic capsule (CAP) and anterior fibromuscular stroma (AFS) were also analyzed because of their close relationships with the prostatic and periprostatic tissues.
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RESULTS |
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DENONVILLIERS' FASCIA (DF)
On the posterior surface of the prostate, DF, which is composed of collagenous fibers and occasional muscle fibers, was noted in all cases. Furthermore, it was recognized not as a single-layer fascia, but as a fascicle—a multi-layer fascia with interlacing branches.
Regarding the relationships with its surroundings, the DF fused with the CAP at the center of the prostatic posterior surface in 77 of the 79 cases (97%). In the remaining two cases (3%), the DF remained at a distance from the CAP in this region. On the other hand, in the lateral region of the prostatic posterior surface, the DF was separated from the CAP, leaving a few fibers partly linking them, and the space between them was filled by adipose tissue in all cases (Fig. 1) (Table 1).
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LATERAL PELVIC FASCIA (LPF)
On the lateral surface of the prostate, the LPF was recognized as collagenous fibers and not simply as a single-layer fascia, but as a fascicle—a multi-layer fascia similar to the DF.
Regarding the relationships between the LPF and the CAP, although there were varying amounts of adipose tissue between them, they connected and fused with each other in all cases, to varying degrees. The current cases were divided into two groups according to the degree of distance between the LPF and the CAP and the amount of adipose tissue lying between them. In 41 cases (52%), the LPF remained at a distance from the CAP and the space between them was occupied by adipose tissue (Fig. 2). In the remaining 38 cases (48%), the LPF fused with the CAP and little adipose tissue was present between them (Fig. 3) (Table 1).
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On the anterior surface of the prostate, the LPF extended to the anterior and covered the entire anterior aspect in 62 cases (79%) (Fig. 4). In the remaining 17 cases (21%), we could not recognize whether the LPF covered the entire anterior aspect because of a partial lack of the LPF itself, suggesting an operative artifact (Table 1).
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NEUROVASCULAR BUNDLE (NVB)
Blood vessels, including both arteries and veins, and nerve trunks were recognized in the postero-lateral region and the lateral aspect of the prostate, embedded in varying amounts of adipose tissue. The space where they were located was the outside of the CAP and the inside of the DF and the LPF. Some blood vessels were embedded in the CAP or penetrated the CAP into the prostate, especially into the peripheral gland. The spread or location of the vessels and the nerve trunks varied in each case, and a ‘bundle’ formation was not always recognized in all cases, although larger vessels and nerve trunks tended to be located at the postero-lateral region. Thus, we divided the current cases into two groups, according to the spread and location of the vessels and the nerve trunks. In 41 cases (52%), these vessels and nerve trunks sparsely spread from the lateral aspect of the prostate to the anterior, without a definite bundle formation (Fig. 5). On the other hand, 38 cases (48%) presented localization of these vessels and nerve trunks in the postero-lateral region of the prostate (Fig. 3) (Table 1). The ‘neurovascular bundle’ could be recognized only in the latter group.
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ANTERIOR FIBROMUSCULAR STROMA (AFS)
AFS is not a periprostatic tissue, but rather, a part of the prostate. However, we analyzed this structure because of its important relationships with its surroundings, including the CAP, the LPF and the blood vessels of the anterior surface of the prostate.
The AFS was observed at the anterior aspect of the prostate, and was found to be composed of collagen fibers and smooth muscle fibers with occasional benign prostatic glands, infiltrating cancer glands and striated muscle. Regarding the relationships with its surroundings, laterally, we recognized a smooth transition from the CAP to the AFS in all cases, and the AFS increased in thickness medially. Thus, we could not recognize the CAP at the anterior aspect of the prostate in 70 cases (89%). In the remaining 9 cases (11%), we could distinguish the CAP from the AFS. In addition, the AFS connected and fused with the LPF, which covered the outermost regions of the lateral and anterior surfaces of the submitted specimens in 67 cases (85%) (Fig. 4). In 12 cases (15%), we could not recognize the connections between the AFS and the LPF because of a partial lack of the LPF, which appeared to be an operative artifact (Table 1).
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DISCUSSION |
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In radical retropubic prostatectomy, dissection of the posterior surface of the prostate is performed at the layer between the rectum and the DF, and the prostate is removed with the DF. At the center of the prostatic posterior aspect, the DF fused with the CAP in 97% of the cases. In 3% of the cases (two cases), although we recognized that the DF remained at a distance from the CAP at the center, no adipose tissue was present between the CAP and the DF. Therefore, we considered that these observations were due to the artifacts during operative manipulation or histopathological sectioning. On the other hand, in the lateral region of the prostatic posterior aspect, the DF and the CAP were clearly separated by adipose tissue, but were linked with each other by delicate fascicles in all cases. Thus, it was considered that the relationships between the DF and the CAP at the posterior aspect were characterized by fusion with each other at the center and separation at the lateral region. According to these findings, in order to move the prostate without major damage in radical retropubic prostatectomy, it is necessary to incise the DF at the apex and the base, and to dissect the outer layer of the DF. Dissection of the layer between the DF and the CAP, especially at the center, would injure the outermost portions of the prostate, possibly resulting in an iatrogenic positive surgical margin.
The LPF is recognized as covering the lateral aspect of the prostate in radical retropubic prostatectomy. In the current study, the LPF was recognized as a multi-layer fascia, similar to the DF, and was linked to the CAP by delicate collagenous fibers in all cases. The cases were divided into two groups on the basis of the relationship between these two structures. In one group (52% of the cases), the main fascicle of the LPF remained at a distance from the CAP, and adipose tissue was present between them. In the other group (48% of the cases), the LPF fused with the CAP, and little adipose tissue was present between them.
The LPF covered the prostatic anterior aspect in 79% of the cases. In the remaining cases, the LPF was not observed on the anterior surface; however, we presume that the LPF covers the anterior aspect in all cases, and this is why the lack of LPF on the anterior aspect in these cases appears to be an artifact caused during the operation.
The NVB, which can be partially seen through the LPF in radical retropubic prostatectomy, is generally believed to exist locally near the postero-lateral region. However, in the current study, it only existed in the localized region in approximately half the cases (48%). Conversely, it was sparsely spread on the entire lateral aspect without localization in the remaining cases (52%). The ratio of these two groups was nearly equal to that of the relationships between the LPF and the CAP. This result is essentially the same as that of Hong et al. who reported on the anatomic distribution of periprostatic adipose tissue (5). This implies that in the cases where the CAP and the LPF adhered to each other on the lateral aspect, the NVB existed locally in the postero-lateral region with true bundle formation. On the other hand, in the cases where the CAP and the LPF remained at a distance on the lateral aspect, the NVB sparsely spread to the space without localization. Consequently, we conclude that the degree of fusion between the CAP and the LPF is closely related to the site and the localization of the NVB.
In non-nerve-sparing radical retropubic prostatectomy, dissection of the lateral aspect of the prostate is performed outside the LPF so that the NVB is removed in a manner in which it remains attached to the prostate. In the nerve-sparing procedure, the LPF is divided near the postero-lateral region of the prostate, where the surgeon thinks that the NVB is located, and the bundle is dissected from the CAP, so that it is preserved. In the current study, we recognized that the NVB is situated at the localized space in approximately half the cases, whereas in the others, it sparsely spread to the lateral aspect without definite bundle formation. Therefore, we suggest that surgeons cannot always complete the nerve-sparing procedure in all cases by simple dissection in the postero-lateral region. Therefore, in order to preserve the NVB completely, it is important to widely dissect the lateral aspect of the prostate in half the patients. We consider this to be one of the reasons why some patients lose potency even if the nerve-sparing procedure is performed. In fact, the nerve trunks located in the postero-lateral region tend to be larger than those of the entire lateral aspect, and almost all of the smaller trunks may be branches to the prostate itself and not related to erectile function. However, at least some of these smaller trunks are thought to be related to erectile function. The literature reveals potency rates of 11–58% after preserving the unilateral NVB, and 68–82% after preserving the bilateral NVBs (6–11). The period and survey methods of these data vary; however, it can be stated that the more the nerve trunks that are preserved, the higher are the potency rates.
In another investigation with nerve-spared specimens (data not shown), dissection between the CAP and the LPF was performed in the theoretically correct layer. However, damage to several regions of the CAP was observed. In almost all cases, large blood vessels and thick connective tissue were observed in the vicinity of such damaged regions. Although this may be an artifact arising during preparation of the histopathological specimens, the possibility of actual iatrogenic damage cannot be excluded, which might have been inflicted during the dissection of the region where the blood vessels enter and leave, or where the CAP is tightly fused with the LPF. The region is close to the prostatic glands, and is frequently infiltrated with carcinoma cells (12). It has been reported that cancer control is equal with or without the nerve-sparing procedure (13,14); however, we should recognize the possibility that such damage could cause a positive surgical margin, such as that reported by McNeal (15).
In nerve-sparing procedures, it is also necessary to dissect the DF at the postero-lateral region, where the DF parts from the CAP. Although it may be difficult to grossly recognize the border, incorrect dissection of the region could cause damage to the CAP, probably resulting in a positive surgical margin. Villers et al. reported that the DF is useful for preventing cancer penetration in the posterior surface (2). Therefore, care should be taken not to excessively dissect the layer between the CAP and the DF.
On the anterior aspect, we recognized a smooth transition from the CAP to the AFS, and the AFS increased in thickness medially in all cases, as reported by McNeal (15). Although the main components of the AFS were collagen fibers and smooth muscle fibers, it also occasionally contained benign prostatic glands, infiltrating cancer glands and striated muscle. The AFS is dissected at the prostatic apex and the prostatic base in radical retropubic prostatectomy. Incorrect dissections may leave prostatic glands, including carcinomatous ones, at the prostatic apex or the bladder neck.
We make thorough use of transrectal ultrasoud (TRUS) imaging for clinical evaluation of prostate cancer. This method also enables us to undertake a detailed study of the periprostatic structural features in some subgroups of patients. Based on the current results, it can be stated that if LPF and CAP are separated at the lateral aspect, the space between them contains adipose tissue, blood vessels and nerve trunks. Conversely, if LPF and CAP adhered except for the postero-lateral angle, these soft tissues were seldom located at that site. However, ultrasonographic findings do not always correspond with histopathological results, because the specificity and sensitivity of the ultrasonographic examination depend on the amount and/or the size of the prostates and the periprostatic structures. However, it is true that useful information such as the localization of NVB can be obtained through preoperative TRUS in some subgroups. We firmly believe that the results of the current study contribute to the preoperative diagnosis and the treatment of prostate cancer, especially localized disease, clarifying issues pertaining to the curability and QOL, such as erectile function.
We have used the term ‘prostatic capsule (CAP)’ in the current study. However, as Ayala et al. reported, the prostate does not have a well-defined capsule (16). The structure that we called the ‘capsule’ is a fibromuscular layer, which is recognized at the outermost region of the prostate (15). In fact, in some areas, the so-called ‘capsule’ could not be recognized as it merged with the DF, the LPF or the AFS in coronal sections. Furthermore, we could not recognize the ‘capsule’ at the apex and the base of the prostate in sagittal sections, since the outermost region of the prostate blends smoothly with the pelvic floor and the bladder wall. However, as Ayala et al. (16) have described, we also consider that the semantics regarding the so-called ‘capsule’ are not important for the precise and actual interpretation of the prostate and periprostatic anatomy, as long as its histological configuration and features are accurately understood; and this is the reason why we used the term ‘prostatic capsule.’
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CONCLUSION |
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TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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We investigated the anatomical features of the periprostatic tissues in radical retropubic prostatectomy specimens. The results support the rationale of this procedure and indicate that there is still much scope for improvements in radical prostatectomy and pathological examinations.
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References |
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