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Diphallia: literature review and proposed surgical classification system

Abstract Background Diphallia occurs once in 5–6 million births, with no two patients presenting with the same anatomical variation. Here we discuss a review of diphallia case reports, as well as present a new surgical classification system based on the soft tissue composition of the two phalluses, the anatomy of the urethra present within the most normal phallus and the bladder configuration. Methods Eighty‐seven diphallia case reports were collected and analysed, excluding those presented in animals and articles that were non‐English, with the results compiled to provide an in‐depth reference of the specific anatomy found in diphallia patients and the associated abnormalities. Results Our proposed classification system was then applied to each patient and the most common configuration base on our classification system presented, along with commonly seen associated anomalies. Conclusion The reviewed cases represent a subset of the most unique diphallia patients; thus, several cases may be left unreported. Future reports can then be categorized, aiding as a reference, and potentially building on the classification, should the patient not fit into a specific group, leading to an expansion of the classification system.


Introduction
Diphallia or duplicate penis is an extremely rare embryological anomaly with a wide range of anatomic appearances ranging from small accessory tissues to complete duplications of the phallus, glans, urethras, and bladders, as well as an extensive list of associated abnormalities. The phalluses are usually unequal in size and positionally, can lie side by side, stacked on top of the other in the sagittal plane, or with little association to each other. 1 This paper assesses patients within the literature to summarize diphallia variants, as well as build on the existing classification of diphallia to include a more specific categorization of the phallus soft tissue, the urethral anatomy, and the bladder configurations to create a surgical classification system.

Background
Diphallia is estimated to occur in 1 out of 5-6 million births, with around 100 patients being reported within the literature. The oldest published instance of diphallia was reported in 1609 by Johannes Jacob Wecker; 'in Bologna during public dissections the cadaver of a man who had a double penis', however the earliest pictorial record of diphallia dates back to 1862 in the Lupanar (Latin for brothel) in Pompeii, in which a painting on the wall depicted a completely diphallic man (Fig. 1). 2 Embryology Previously, Cecil 3 submitted four embryological explanations for diphallia. The first includes the bladder, the prostatic urethra, and the penis being derived from a bilateral anlagen, which normally gives a single end product by fusion, meaning diphallia is a product of an incompletely fused anlagen. Next, diphallia may be an atavism, as snakes and lizards normally possess double penis or possibly represents a teratoid structure. Cecil also suggested that it may be a minor degree of duplication, much like supernumery digits, of the individual.
Hollowell et al. however affirm that these explanations are incomplete and suggests that that embryologically, the diphallia anomaly occurs in the fetus between the third and seventh week of gestation, in which an insult hampers normal functioning of the caudal cell mass of the fetal mesoderm at the time of the urogenital sinus separating from the genital tubercle into the penis. Complete diphallia may then stem from longitudinal duplication of the infraumbilical cloacal, with the subsequent mesodermal migration leading to the formation of two separate and complete sets of genital tubercles, genital folds, and genital swellings. 3,4 Treatment Treatment of diphallia is typically approached on an individual basis, as no two patients within the literature are the same. The associated anomalies are a major cause of mortality in diphallia patients, and treatment is usually done in a stepwise manor, with corrections aimed at the anomalies, excision of the more abnormal phallus, excision of the urethra in instances of duplicate urethra, and excision or correction of either duplicate bladders or bladder exstrophy. 1 It may also be difficult to discern which phallus to excise, thus with the proposed classification system, a label can be used to drive the treatment approach, allowing a decision to be made based on the more normal phallus, with the more normal urethral pathway and normal bladder configuration.

Methods
For this paper, a review of published diphallia patients was conducted by one reviewer. Google scholar and PubMed were analysed using key phrases diphallia, double penis, psuedophallia and bifid glans giving a total of 518 articles. Articles were screened based on title and abstract, making sure to include relevant case reports in humans, excluding articles in animals, duplicate articles and non-English articles. Following the screening of relevant inclusion and exclusion criteria, a total of 76 articles were analysed, which totalled 87 relevant diphallia patients found within the literature. Each patient was then analysed and presented in Table 1. From each patient, the unique anatomical variant for each was then examined. This included first addressing the age of the patient at the time of presentation, followed by categorizing the soft tissue structure of each phallus, the anatomy of the scrotum and testicles, as well as if there was a penoscrotal transposition. The reports were also analysed for their urethral anatomy, and if there was a hypospadias or epispadias present, as well as the bladder configuration. Lastly, the associated abnormalities were summarized based on the reviewers best clinical judgement. Each patient was then classified based on the proposed classification system below.

Classification
Schneider 80 has previously classified diphallia into four main categories: (1) Duplication of the glans alone (2) Bifid diphallia (3) Complete diphallia with each penis having two corpora cavernosa and a corpus spongiosum (4) Pseudodiphalia in which there is a rudimentary accessory atrophic penis existing independently of the normal penis Our proposed classification is based on anatomical variants found within the literature on diphallia, which builds on Schneider's classification in order to provide a more specific description of the phallus soft tissue, as well as include a description of the pathway of the most normal urethra and the bladder configuration. The classification method has been proposed to be used to simplify the categorization of diphallia patients, using the system to classify the most intact phallus, the most normal urethra, and whether there is an additional surgical step regarding the bladder. The system will place the anatomy of diphallia into specific categories based on the structure of the phallus, the urethral anatomy and the bladder formations. Table 2 below displays the proposed categories.

Results
With a review of the literature, and application of the proposed classification system, common diphallia configurations can be displayed. While these individuals may still differ in terms of specific anatomy, such as the relation of the phalluses to one another, the  specific pathway of the urethras or the associated anomalies, the classification and the frequency in which they occur is based on the soft tissue make-up of the phalluses, the urethra as it pertains to the   most normal urethra and the bladder configuration. Of the reviewed literature with sufficient information, our classification showed that diphallia patients categorized as 1Aα contributed to the largest percentage of reports at 26.4%. The next most frequent pattern seen was 1Aβ, where the soft tissue and urethra were structurally normal, however there was a duplicate bladder, which made up 12.6% of the patients reviewed. The 2Aα configuration was the next most seen classification within the literature, appearing in 7% or 8.0%, followed by configurations 1Cα, 3Aα, 7Aα, which each contributed to 4.6% of the patients. The remaining reports and the corresponding classifications can be reviewed in Table 3. Table 4 then depicts the most common configurations found within the literature and additional examples of diphallia, which shows a graphic of the corresponding anatomy, an example of the gross anatomy extracted from their corresponding reference and the patient that correspond to the detailed classification.

Associated anomalies
Upon review of the literature, several diphallia patients present with no other associated anomalies. However, several abnormalities can be seen in other diphallia patients. These anomalies arise from both genitourinary and gastrointestinal systems, as well as some reports seeing musculoskeletal or cardiovascular anomalies. The majority of the malformations fall within the former two. Genitourinary abnormalities include the presence of either a duplicate bladder 10,13,17,[22][23][24]31,36,41,47,54,63,72 or bladder exstrophy, 13,42,49,62,70,72,77 as well as duplicate ureters, 36,56 vesicoureteral reflux, 47,72 and ureteric stenosis. 77 Further anomalies within the urinary system include issues and malformations pertaining to the kidneys, which include single kidney agenesis, [7][8][9]37,54,63,72 duplicate unilateral kidney, 36 pelvic kidney 24 and horseshoe kidney. 31,41,52 Fistulas pertaining to the urinary system were also a common association with rectovesical and urethrorectal 10,31,72 being noted. Next, there is also a wide range of gastrointestinal abnormalities that appear to arise in patients with diphallia. The most seen is the presence of an imperforate anus. 5,13,17,24,37,38,44,47,49,50,54,72 There can also be further duplication of various aspects of the gastrointestinal system associated with diphallia, which includes duplication of the rectum, colon, cecum, appendix, and terminal ileum. 10,14,31,37,47,54,60,67 Along with the mentioned fistulas mentioned above, perineal 13 and tracheoesophageal fistula 37,50 have been reported as associated abnormalities pertaining to the gastrointestinal tract. It was also noted that there were hernias associated with diphallia patients, mostly those occurring at the umbilicus, 7,25,41,53 however inguinal hernias 54,72,79 are also cited within the literature. Further gastrointestinal anomalies then include ectopic bowel segments, 59,74 omphalocele 37,72 and Meckel diverticulum. 55 In terms of musculoskeletal and cardiovascular abnormalities, there is a wide range of malformations shown in the literature that  are associated with diphallia. Two common associations include both hemivertebra 8,54,62 and a wide diastasis of the pubic bone 11,17,22,63 with further musculoskeletal malformations comprising of menigocele 6,13 and talipes equinovarus 77,79 and less commonly pre-axial polydactyly, 9 partial sacral agenesis, 11 agenesis and hypotrophy of digits or limbs, 25,31,45,72,79 or bilateral congenital hip dislocations. 79 Cardiovascular malformations are more rare, however present in multiple patients, which include abnormalities such as atrial septal defects. 9,51 A summary of associated abnormalities pertaining to specific patients is outlined in Table 1. Table 5 then displays the most commonly seen abnormalities seen in concordance with diphallia. Most commonly, an imperforate anus was seen associated with diphallia patients which was shown in 13.8% of the reviewed patients. Next, 9.2% of the patients also saw further duplication along the gastrointestinal tract, with duplications of either the rectum, colon, cecum, appendix or terminal ileum being reported. Single kidney agenesis and inguinal hernias were then the next most seen abnormalities, arising in 8.0% and 6.9% of the patients, respectively. Lastly, the most common musculoskeletal anomaly associated with diphallia was limb agenesis or hypotrophy, which appeared in 5.7% of the diphallia cases.

Discussion
The paper highlights an overview of diphallia, illustrating different aspects of the anomaly including history, embryology and treatments. It also expands to provide a classification system that is built on previous works to give a system in which future patients can be categorized and compared. The results then feature the most common anatomical variations, showing that roughly 25% of the published instances have two phalluses with 3 corpora, at least a single normal urethra and a single bladder. The literature review and the published articles however may be biased as typically the more unique and interesting patients are presented, leaving a potentially large number of unpublished reports that could contribute to the current review and proposed classification system. The results regarding associated anomalies potentially hold a similar bias, in that unique abnormalities may have been focused on, leaving out seemingly minute associations. Lastly, as new patients may be presented, and different variants may arise in which the proposed classification system may or may not encompass, or penile anomalies such as triphallia or triple penis, as reported by Jabali et al. 81 get reported, the current proposed classification may need to be modified.

Conclusion
Following a literature review, each diphallia patient is a unique variant with its own anatomical configuration and associated anomalies. This has led to the proposed classification system that builds on previous bodies of work to categorize each patient based on the most normal aspects of the diphallia. By classifying the structure of the phallus that is to be kept, the pathway of the urethra present within the most normal phallus and the bladder morphology, a surgical approach can be broached and executed to ensure a satisfactory functional goal, with preserved continence, erectile function, and cosmetic outcomes.