portion of the penis may be involved.
Congenital Vascular Shunts
Anomalous vascular anastomoses between the peripenile circulation and the erectile tissues of the CCP result in shunts that allow blood from the CCP to exit the erectile tissues and destroy the integrity of the closed hydraulic system necessary for complete erection [27]. Vascular shunts may occur as a congenital anomaly or form following an injury that disrupts the integrity of the tunica albuginea of the penis. Regardless of etiology, when erection is stimulated at a test breeding or with an electroejaculator, partial erection and protrusion of the glans penis is initiated followed by loss of intrapenile pressure and failure to achieve full erection.
Vascular anastomoses between the CCP and extracorporeal vasculature found in the distal free portion of the penis are usually multiple and result from congenital flaws in the integrity of the tunica albuginea [28]. As blood escapes through these distally located shunts at the time of sexual stimulation, “blushing” of the preputial tissues may be observed as blood from the CCP enters the venous circulation beneath the preputial skin. A presumptive diagnosis may be made following observation of a test mating or attempts to induce erection with an electroejaculator. Confirmation requires demonstration of the shunts with radiographic contrast studies in which radiopaque contrast media are injected directly into the CCP as serial radiographs are taken. In the normal penis the contrast media remain within the CCP until eventually exiting at the crura of the penis (Figure 15.12). Visualization of the contrast media within the peripenile vasculature outside the CCP is diagnostic (Figure 15.13). Demonstration of anomalous vessels in the distal portion of the penis may be enhanced by occlusion of the distal peripenile vessels by application of a tourniquet to the penis proximal to the location of the shunt(s) [29]. Unlike acquired vascular shunts of the CCP, congenital shunts are seldom amenable to surgical correction.
Figure 15.12 Normal cavernosogram. Contrast media injected into the CCP at the level of the free portion of the penis remain within the CCP. The ventral canals and cavernous spaces are clearly outlined.
Figure 15.13 Cavernosogram demonstrating multiple shunts from distal cavernous spaces to the peripenile vasculature.
Source: Courtesy of Robert L. Carson and Dwight Wolfe.
Anatomic and Developmental Abnormalities
At the time of puberty androgens initiate growth of the juvenile penis and initiate separation of the penile and preputial epithelium [7], as discussed in the section “Abnormalities of the Prepuce.” The sigmoid flexure develops as the penis enlarges and the retractor penis muscles attached to the proximal flexure of the sigmoid maintain the non‐erect penis within the sheath. The rigid tunica albuginea has sufficient strength to effectively contain the pressures generated at the time of erection and gives the erect penis its tubular shape. Uniform filling of the cavernous spaces of the CCP is required for complete erection. The dorsal apical ligament of the penis must elevate the free portion of the erect penis to allow successful intromission.
Penile Deviation
Deviation of the penis results in inability to copulate. Affected bulls may have a history of one or more successful breeding seasons and there is often no history of trauma or penile injury. In the bull the dorsal apical ligament of the penis originates from the tunica albuginea proximal to the free portion of the penis, runs along the dorsum of the free portion beneath the penile skin, and rejoins the tunica albuginea near the distal end of the CCP. The ligament inserts on the distal penis centrally with a broad set of fibers and on the left lateral aspect of the free portion of the penis with a narrower and better defined set of fibers [9, 30]. This ligament gives support to the erect penis and maintains the normal alignment of the penis as the bull positions himself for coitus and utilizes the tip of the penis to search for the vulva. Following intromission and achievement of peak erectile pressure the ligament may “slip” to the left and the distal penis will often assume a corkscrew shape and spiral within the vagina at the time of the ejaculatory lunge [6]. When erection is induced with the artificial stimulus of an electroejaculator, the penis will frequently assume this same spiral orientation, often prior to ejaculation.
Spiral Deviation
Pathologic spiral deviation of the penis occurs when the dorsal apical ligament slips laterally prior to intromission (Figure 15.14a). The role of the dorsal apical ligament in the development of spiral deviation is well described, but the factor or factors leading to the premature occurrence of this otherwise normal phenomenon are poorly understood [9, 30, 31]. Malfunction of the dorsal apical ligament due to a shortening of the ligament or lengthening of the penis as the bull ages was once commonly felt to be the cause but remains unproven. More recent speculation suggests that intravaginal spiral deviation occurs normally in many bulls, associated with peak erectile pressure, and that pathologic spiral formation occurs prematurely in bulls in which peak erectile pressure occurs prior to intromission. In either case, bulls with premature spiral deviation of the penis are unable to complete the copulatory act.
Figure 15.14 (a) Spiral deviation of the penis demonstrated during a test mating. (b) Spiral deviation of the penis induced with an electroejaculator during semen collection. Spiraling of the penis during electroejaculation is common and should not be confused with the pathologic deviation prior to achieving intromission shown in (a).
Source: Image courtesy of Clint Hilt.
A diagnosis of spiral deviation is suspected based on history and a description of the penis during the breeding attempt, but diagnosis can only be confirmed by an observed test mating. Because the penis of many normal bulls will spiral under the artificial stimulus of electroejaculation, diagnosis following observation of spiraling during stimulation with an electroejaculator is insufficient (Figure 15.14b). Deviation may be intermittent, especially early in the development of the condition, and repeated observations of test matings may be required to confirm the diagnosis.
No medical therapy is available to correct spiral deviation of the penis. Surgical correction of spiral deviation relies on induction of fibrous tissue to strengthen the attachments of the dorsal apical ligament to the penis. The available surgical techniques are described in Chapter 19. Spiral deviation is sometimes seen in association with damage to the dorsal nerves of the penis and careful observation at the time
