Advances in understanding of mammalian penile evolution, human penile anatomy and human erection physiology: clinical implications for physicians and surgeons

Penile cavernous sinusoids are Prox1-positive hybrid vessels

Endothelial cells (ECs) of blood and lymphatic vessels have distinct identity markers that define their specialized functions. Recently, hybrid vasculatures with both blood and lymphatic vessel-specific features have been discovered in multiple tissues. Here, we identify the penile cavernous sinusoidal vessels (pc-Ss) as a new hybrid vascular bed expressing key lymphatic EC identity genes Prox1, Vegfr3,and Lyve1. Using single-cell transcriptome data of human corpus cavernosum tissue, we found heterogeneity within pc-S endothelia and observed distinct transcriptional alterations related to inflammatory processes in hybrid ECs in erectile dysfunction associated with diabetes. Molecular, ultrastructural, and functional studies further established hybrid identity of pc-Ss in mouse, and revealed their morphological adaptations and ability to perform lymphatic-like function in draining high-molecular-weight tracers. Interestingly, we found that inhibition of the key lymphangiogenic growth factor VEGF-C did not block the development of pc-Ss in mice, distinguishing them from other lymphatic and hybrid vessels analyzed so far. Our findings provide a detailed molecular characterization of hybrid pc-Ss and pave the way for the identification of molecular targets for therapies in conditions of dysregulated penile vasculature, including erectile dysfunction.

Anatomy applied to image diagnosis of the hind limb in the black-striped capuchin (Sapajus libidinosus Spix, 1823)

The knowledge of anatomy and imaging exams emerges as an important tool in the study of evolutionary processes of a species, in the elaboration of diagnosis, and the successful choice of the appropriate clinical and surgical procedures. Therefore, this study aims to describe the osteology of the hind limb of Sapajus libidinosus by means of gross, radiographic, and tomographic images. Four cadavers were used in the macroscopic analysis and five animals for the imaging exams, of which four were eventually euthanized and added to the macroscopic study. For imaging exams, they were kept anesthetized. All bones of the hind limb were documented, their structures were described, and compared with data in the literature from human and nonhuman primates. We have performed Student's t test for independent samples. There was no statistical difference between the sexes regarding the length of the hind limb bones. The coxal bone was largely well described using imaging methods. A small penile bone was present at the tip of the penis and it could be identified by all analysis methods. The femur, as well as the tibia and fibula, were not well portrayed in their proximal and distal epiphyses by radiography (Rx). However, they were well identified on tomography. No third trochanter was observed in the femur and the patella had a triangular shape. All the structures described by gross anatomy of the tarsus and metatarsus could be identified by Rx and tomography. More subtle structures, such as the popliteal notch on the tibia, and the gluteal tuberosity pectineal line and facies aspera on the coxal bone, were not identified by medical imaging. S. libidinosus presented anatomical characteristics that were similar to those of larger New World and Old World monkeys, including man. This suggests it's value as an experimental model for studies in recent primates.

Effects of unilateral/bilateral amputation of the ischiocavernosus muscle in male rats on erectile function and conception

Background

The ischiocavernosus muscle (ICM) encompasses a pair of short pinnate muscles attached to the pelvic ring. The ICM begins at the ischial tuberosity and ends at the crus of the penis while covering the surface of the crus. According to the traditional view, the contraction of the ICM plays an auxiliary role in penile erection. However, we have previously shown that the ICM plays an important role in penile erection through an indirect method of diagnosing erectile dysfunction (ED) caused by ICM injury by observing the infertility of paired female rats. Since intracavernosal pressure (ICP) is the current gold standard for diagnosing ED, this study aimed to amputate unilaterally/bilaterally the ICM to establish an ED model by detecting the ICP, recording the infertility of matching female rats, and comparing the two methods.

Results

Forty sexually mature adult male rats were selected and randomly divided into the following groups: the control group (n = 10), sham operation group (n = 10), unilateral ischiocavernosus muscle (Uni-ICM) amputation group (n = 10), and bilateral ischiocavernosus muscle (Bi-ICM) amputation group (n = 10). Eighty female reproductive rats were randomly assigned to the above groups at a ratio of 2:1. We evaluated the time to conception for the paired female rats and the effects of unilateral/bilateral severing of the ICM on erectile function. The results showed that the baseline and maximum intracavernosal pressure (ICP) in the control group, sham operation group, Uni-ICM amputation group, and Bi-ICM amputation group were 17.44±2.50 mmHg and 93.51±10.78 mmHg, 17.81±2.81 mmHg and 95.07±10.40 mmHg, 16.73±2.11 mmHg and 83.49±12.38 mmHg, and 14.78±2.78 mmHg and 33.57±6.72 mmHg, respectively, immediately postsurgery. The max ICP in the Bi-ICM amputation group was lower than that in the remaining three groups (all P<0.05). The pregnancy rates were 100, 100, 90, and 0% in the control group, sham operation group, Uni-ICM amputation group, and the Bi-ICM amputation group, respectively. The pregnancy rate in the Bi-ICM amputation group was significantly lower than that in the remaining groups (all P<0.05). The time to conception was approximately 7–10 days later in the Uni-ICM amputation group than in the control and sham groups (all P<0.05).

Conclusions

Male rats undergoing Bi-ICM amputation may develop permanent ED, which affects their fertility. In contrast, rats undergoing Uni-ICM amputation may experience transient ED.

Surgical niche for the treatment of erectile dysfunction

Penile erection implicates arterial inflow, sinusoidal relaxation and corporoveno-occlusive function. By far the most widely recognized vascular etiologies responsible for organic erectile dysfunction can be divided into arterial insufficiency, corporoveno-occlusive dysfunction or mixed type, with corporoveno-occlusive dysfunction representing the most common finding. In arteriogenic erectile dysfunction, corpora cavernosa show lower oxygen tension, leading to a diminished volume of cavernosal smooth muscle and consequential corporoveno-occlusive dysfunction. Current studies support the contention that corporoveno-occlusive dysfunction is an effect rather than the cause of erectile dysfunction. Surgical interventions have consisted primarily of penile revascularization surgery for arterial insufficiency and penile venous surgery for corporoveno-occlusive dysfunction, whatever the mechanism. However, the surgical effectiveness remained debatable and unproven, mostly owing to the lack of consistent hemodynamic assessment, standardized select patient and validated outcome measures, as well as various surgical procedures. Penile vascular surgery has been disclaimed to be the treatment of choice based on the currently available guidelines. However, reports on penile revascularization surgery support its utility in treating arterial insufficiency in otherwise healthy patients aged <55 years with erectile dysfunction of late attributable to arterial occlusive disease. Furthermore, it is noteworthy that penile venous surgery might be beneficial for selected patients with corporoveno-occlusive dysfunction, especially with a better understanding of the innovated venous anatomy of the penis. Penile vascular surgery might remain a viable alternative for the treatment of erectile dysfunction, and could have found its niche in the possibility of obtaining spontaneous, unaided and natural erection.

Anatomy of the cavernous muscles of the kangaroo penis highlights marsupial-placental dichotomy

The mammalian penis is a complex hydraulic organ of cavernous (spongy) tissue supported by both smooth and skeletal muscle structures. In placental mammals, the paired ‎Musculus ischiocavernosi anchor the corpora cavernosa to the pelvis (at the ischium), and the paired M. bulbospongiosi converge as they envelop the base of the corpus spongiosum. Male marsupials have a dramatically different anatomy, however, in which both sets of paired muscles remain separate, have a bulbous, globular shape and do not have any direct connection to the pelvis. Here we provide the first detailed anatomical investigation of the muscles of the penis in the western grey kangaroo (Macropus fuliginosus) incorporating dissection, histology, vascular casting and computed tomography. The M. ischiocavernosus and M. bulbospongiosus form massive, multipennate bodies of skeletal muscle surrounding the paired roots of the corpus cavernosum and corpus spongiosum, respectively. Bilateral vascular supply is via both the artery of the penis and the ventral perineal artery. Histological examination reveals cavernous tissues with substantial smooth muscle supported by fibroelastic trabeculae, surrounded by the thick collagenous tunica albuginea. The M. ischiocavernosus and M. bulbospongiosus are known to function during erection of the penis and ejaculation via muscular contraction increasing blood pressure within cavernous vascular tissues. The thick muscular anatomy of the kangaroo would be well suited to this function. The absence of any connection to the bony pelvis in marsupials suggests the possibility of different mechanisms of action of these muscles with regard to reduction of venous return, eversion from the cloaca, or movements such as penile flips, which have been described in some placental mammals. This highlights a greater diversity in form and function in the evolution of the mammalian penis than has been previously considered.

Ligamentous structures in human glans penis

The corpus spongiosum reportedly occupies a larger proportion of the human glans penis than does the penile body, embedding the end of the corpus cavernosus (CC). However, anatomic descriptions about the fibrous structures of glans penis in the literature cause confusion during dissection and reconstructive surgery. Forty-five penises of formalin-embalmed cadavers were dissected sagittally along the course of the distal urethra and observed macroscopically. Dense connective tissues adjacent to the fossa navicularis and spongiosum parts of the glans were cropped, and underwent Masson's trichrome and Verhoeff-Van-Gieson staining. Most (55.5%) of the specimens had distinct fibrous bands toward the distal tips of the glans penis, which elongated from the tunica albuginea of the CC. They comprised longitudinal collagen bundles continuous to the outer longitudinal layer of the tunica albuginea covering the CC and were intermingled with sparse elastic fibres. This architecture either did not reach the distal end of the glans penis (35.5% of cases), or was obscure or dispersed in all directions (9.0% of cases). The structural dimorphism and the variations in the ratio of dense connective tissue components of the fibrous skeleton are considered to contribute to the varying degrees of flexibility, distensibility and rigidity of the human glans penis.

Visualization of Penile Suspensory Ligamentous System Based on Visible Human Data Sets

Background

The aim of this study was to use a three-dimensional (3D) visualization technology to illustrate and describe the anatomical features of the penile suspensory ligamentous system based on the Visible Human data sets and to explore the suspensory mechanism of the penis for the further improvement of the penis-lengthening surgery.

Material/Methods

Cross-sectional images retrieved from the first Chinese Visible Human (CVH-1), third Chinese Visible Human (CVH-3), and Visible Human Male (VHM) data sets were used to segment the suspensory ligamentous system and its adjacent structures. The magnetic resonance imaging (MRI) images of this system were studied and compared with those from the Visible Human data sets. The 3D models reconstructed from the Visible Human data sets were used to provide morphological features of the penile suspensory ligamentous system and its related structures.

Results

The fundiform ligament was a superficial, loose, fibro-fatty tissue which originated from Scarpa’s fascia superiorly and continued to the scrotal septum inferiorly. The suspensory ligament and arcuate pubic ligament were dense fibrous connective tissues which started from the pubic symphysis and terminated by attaching to the tunica albuginea of the corpora cavernosa. Furthermore, the arcuate pubic ligament attached to the inferior rami of the pubis laterally.

Conclusions

The 3D model based on Visible Human data sets can be used to clarify the anatomical features of the suspensory ligamentous system, thereby contributing to the improvement of penis-lengthening surgery.

Does tunica anatomy matter in penile implant?

Background

Overall prosthesis survival is important in penile implant, which remains the final viable solution to many patients with refractory erectile dysfunction (ED). This paper is to retrospectively study the role of the anatomy of tunica albuginea (TA).

Methods

From March 1987 to March 1991 while the TA was regarded as a circumferential single layer, 21 organically ED men, aged from 27 to 77, received penile prosthesis implantation and were allocated to conventional group. From August 1992 to March 2013 while the tip of Hegar’s dilator was categorically directed medial-dorsally during corporal dilatation derived from newfound TA as a bi-layered structure with a 360° complete inner circular layer and a 300° incomplete outer longitudinal coat, 196 ED males, aged from 35 to 83, underwent penile implant and were categorized to advanced group. The model of prosthesis was recorded. Prosthesis loss rate and survival time were analyzed and the follow up period ranged from 22.4-26.4 (average 24.3) years and 0.4-20.6 (average 15.8) years to the conventional and advanced group respectively.

Results

To the conventional and advanced group, the number of inflatable and rigid type prosthesis used were 2, 19 and 15, 181 respectively, whereas the prosthesis loss was encountered in 50.0% (1/2), 15.8% (3/19) and 0.0% (0/15), 0.6% (1/181) respectively. And the prosthesis survival time were 5.1-6.3 (5.7) years, 1.3-26.4 (15.2) years and 6.1-16.2 (11.2) years, 0.4-20.6 (15.3) years to the conventional and advanced group respectively. Statistical significance was noted on prosthesis loss in groups (P=0.01) while the Mentor Acuform stood out in prosthesis survival.

Conclusions

Anatomy-based managing maneuver appears to deliver better surgery success in penile implant. Tunica anatomy is significant in performing implant surgery.

Novel pilot films providing indispensable information in pharmaco-cavernosography

Background

Conventional pharmaco-cavernosography provides little information on penile venous anatomy, although it is indispensible in documenting veno-occlusive erectile dysfunction (ED). We propose an innovative method, which may provide additional insight into the penile venous structure.

Methods

From July 2010 to November 2012, 96 impotent men, aged 20 to 75 years, underwent this method of pharmaco-cavernosography in which two sets of 60 mL of 50% omnipaque solution administered intracavernously by themselves. The first set of pilot cavernosograms was taken at intervals of five, ten, twenty and thirty seconds after the commencement of the injection. The second set of cavernosograms was taken in the same intervals within 30 minutes following the pilot set, preceded by the injection of 20 µg prostaglandin E1 (PGE1). Analysis was conducted on the drainage veins including deep dorsal vein (DDV), cavernosal veins (CVs) and para-arterial veins (PAVs) accordingly. The veins demonstrated in the pilot cavernosograms, and the second set, were compared in terms of venous numbers and presentation percentage.

Results

There was a statistically significant difference (P<0.001) between the total number of independent venous drainage channels and the presentation percentage of DDV, CVs and PAVs observed in the pilot cavernosograms, and those in second set (4.5 vs. 2.1; 97.47%, 60.33%, and 38.91% vs. 57.06%, 29.34%, and 19.08%, respectively).

Conclusions

Compared with conventional pharmaco-cavernosography methods, pilot cavernosograms are readily able to show detailed penile venous anatomy. It is therefore may be concluded that pilot cavernosograms is a valuable addition to conventional protocols of pharmaco-cavernosography.

Herb formula enhances treatment of impotent patients after penile venous stripping: a randomised clinical trials

Herbs have been regarded as aphrodisiacs in treating impotence for many centuries despite little true scientific evidence. Our latest refined penile venous stripping (PVS) technique is effective in treating impotence, although this procedure remains controversial. A synergic effect of PVS and oral herbs was confirmed in our practice but lacked rigorous scientific proof. The objective of this report was to review our experience with this combination. From August 2010 to May 2014, 263 males underwent PVS. Among these, 67 unsatisfied men chose additional salvage therapy and were randomly assigned to oral herbs (n = 35) or placebo treatment (n = 32) which replaced herb eventually. All were evaluated with the international index of erectile function (IIEF-5) scoring and our dual pharmaco-cavernosography. The pre-op IIEF-5 score for the herb group was 9.7 ± 3.7, post-operative 13.9 ± 3.3 and post-herb 19.6 ± 3.4, while the control group scores were as follows: pre-op 9.3 ± 4.1, post-op 14.5 ± 3.6, post-placebo 15.1 ± 3.5 and post-herb 19.9 ± 3.2. Although there was no significant difference between the two groups pre-operatively, post-operatively and post-herb, a statistically significant difference was found post-salvage therapy (19.6 ± 3.4 versus 15.1 ± 3.6, P < 0.001). It appears that the combination of oral herbs and PVS treatment provides an enhanced outcome to impotent patients refractory to medicine and unsatisfied with PVS monotherapy alone.

Venous ligation: a novel strategy for glans enhancement in penile prosthesis implantation

Although penile implantation remains a final solution for patients with refractory impotence, undesirable postoperative effects, including penile size reduction and cold sensation of the glans penis, remain problematic. We report results of a surgical method designed to avoid these problems. From 2003 to 2013, 35 consecutive patients received a malleable penile implant. Of these, 15 men (the enhancing group) were also treated with venous ligation of the retrocoronal venous plexus, deep dorsal vein, and cavernosal veins. The remaining 20 men formed the control group, treated with only a penile implant. Follow-up ranged from 1.1 to 10.0 years, with an average of 6.7 ± 1.5 years. Although preoperative glanular dimension did not differ significantly between the two groups, significant respective difference at one day and one year postoperatively was found in the glanular circumference (128.8 ± 6.8 mm versus 115.3 ± 7.2 mm and 130.6 ± 7.2 mm versus 100.5 ± 7.3 mm; both P<0.05), radius (38.8 ± 2.7 mm versus 37.1 ± 2.8 mm and 41.5 ± 2.6 mm versus 33.8 ± 2.9 mm; latter P<0.01), and satisfaction rate (91.7% versus 53.3%, P<0.01) as well. Based on our results, selective venous ligation appears to enhance the glans penis dimension in implant patients.

Reconstructive surgery for idealising penile shape and restoring erectile function in patients with penile dysmorphology and erectile dysfunction

Objective

To report an innovative combination of two surgical procedures to treat patients with erectile dysfunction and penile deviation, arising from advances in penile anatomy.

Patients and methods

From October 1998 to October 2011, 132 men (aged 23–39 years) underwent penile venous stripping and corporoplasty. Of these, 37 were allocated to a transverse and 95 to a longitudinal group, with an infrapubic transverse or pubic median longitudinal approach, respectively. The abridged five-item version of the International Index of Erectile Function (IIEF-5) and cavernosography were used for assessment, as necessary. Under acupuncture-aided local anaesthesia, and after a circumferential incision, the deep dorsal vein and cavernous veins were completely stripped, with 6-0 Nylon sutures for ligation, followed by tunical surgery for correcting the penile shape.

Results

In the transverse and longitudinal groups the mean (SD) duration of surgery was 4.6 (0.2) and 4.8 (0.3) h, respectively. Before surgery the mean (SD) IIEF-5 score was 9.4 (2.3) and 9.6 (2.1), which increased to 20.6 (2.4) and 20.8 (2.7), respectively, after surgery. The penile shape (<15°) was deemed satisfactory in 92% (34/37) and 96% (91/95) of patients in the transverse and longitudinal groups, respectively. The cavernosograms consistently showed a good penile shape. There were significant differences in the mean (SD) duration of penile oedema, at 3.2 (1.6) vs. 11.9 (2.1) days, the overall satisfaction rate and the prevalence of hypertrophied scarring (all P < 0.001).

Conclusion

This combination of unique penile venous stripping with a pubic median longitudinal approach and an anatomy-based corporoplasty is ideally suited to the simultaneous restoration of penile erectile function and morphological reconstruction.

Penile vascular surgery for treating erectile dysfunction: Current role and future direction

Penile vascular surgery for treating erectile dysfunction (ED) is still regarded cautiously. Thus we reviewed relevant publications from the last decade, summarising evidence-based reports consistent with the pessimistic consensus and, by contrast, the optimistically viable options for vascular reconstruction for ED published after 2003. Recent studies support a revised model of the tunica albuginea of the corpora cavernosa as a bi-layered structure with a 360° complete inner circular layer and a 300° incomplete outer longitudinal coat. Additional studies show a more sophisticated venous drainage system than previously understood, and most significantly, that the emissary veins can be easily occluded by the shearing action elicited by the inner and outer layers of the tunica albuginea. Pascal's law has been shown to be a significant, if not the major, factor in erectile mechanics, with recent haemodynamic studies on fresh and defrosted human cadavers showing rigid erections despite the lack of endothelial activity. Reports on revascularisation surgery support its utility in treating arterial trauma in young males, and with localised arterial occlusive disease in the older man. Penile venous stripping surgery has been shown to be beneficial in correcting veno-occlusive dysfunction, with outstanding results. The traditional complications of irreversible penile numbness and deformity have been virtually eliminated, with the venous ligation technique superseding venous cautery. Penile vascular reconstructive surgery is viable if, and only if, the surgical handling is appropriate using a sound method. It should be a promising option in the near future.

Evaluation of the effect of different doses of low energy shock wave therapy on the erectile function of streptozotocin (STZ)-induced diabetic rats

To investigate the therapeutic effect of different doses of low energy shock wave therapy (LESWT) on the erectile dysfunction (ED) in streptozotocin (STZ) induced diabetic rats. SD rats (n = 75) were randomly divided into 5 groups (normal control, diabetic control, 3 different dose LESWT treated diabetic groups). Diabetic rats were induced by intra-peritoneal injection of STZ (60 mg/kg) and rats with fasting blood glucose ≥ 300 mg/dL were selected as diabetic models. Twelve weeks later, different doses of LESWT (100, 200 and 300 shocks each time) treatment on penises were used to treat ED (7.33 MPa, 2 shocks/s) three times a week for two weeks. The erectile function was evaluated by intracavernous pressure (ICP) after 1 week washout period. Then the penises were harvested for histological study. The results showed LESWT could significantly improve the erectile function of diabetic rats, increase smooth muscle and endothelial contents, up-regulate the expression of α-SMA, vWF, nNOS and VEGF, and down- regulate the expression of RAGE in corpus cavernosum. The therapeutic effect might relate to treatment dose positively, and the maximal therapeutic effect was noted in the LESWT300 group. Consequently, 300 shocks each time might be the ideal LESWT dose for diabetic ED treatment.