Introduction

Micropenis or penis-to-prepuce mismatch is a rare condition in dogs that is not often associated with clinical signs. The condition is characterized by an abnormally small penis relative to the size of the dog. It is also rare in humans, occurring in 0.15% of males born in the United States. Proposed etiologies for micropenis include pituitary/hypothalamic insufficiency, testicular insufficiency, transient defects in the androgen synthesis or action during embryogenesis, and idiopathic.^1,2 In dogs, early neutering has been shown to result in immature penile development, but no clinical significance was reported.³ Sertoli cell tumors and hyperestrogenism have also been reported to result in secondary penile atrophy.⁴ Specifically, exposure to estrogen in a rat significantly down-regulated smooth muscle differentiation leading to loss of the cavernous smooth muscle cells of the corpora cavernosa of the body of the penis.⁵ Additionally, defects of the penis and prepuce were overrepresented in cryptorchid dogs, although the study did not specify the type of defect.⁶

Because psychological concern is not a necessary consideration in veterinary medicine, most cases of micropenis are clinically insignificant when micturition is unaffected. However, a disproportionately low penis-to-prepuce ratio can be clinically significant through accumulation of urine in the prepuce, leading to urinary tract infections (UTIs) and abnormal urination. A similar condition in humans is megaprepuce, defined by a redundancy of inner preputial skin and phimosis with a normal penis size and has clinical signs similar to that of a low penis-to-prepuce ratio.⁷

The only previous mention of a micropenis in veterinary literature was a case report describing an infantile penis in an 11 mo old male Doberman pinscher. The clinical signs were dribbling urine, dysuria, hematuria, and urine scalding of the prepuce. Preputial shortening and a wedge prepucectomy were performed surgically. This patient was unable to urinate normally for 3 days following surgery. Additionally, the surgical site dehisced 10 days after surgery, requiring a revision to be performed. Long-term success or follow-up of this case was not reported.⁸

This case report describes the condition of a micropenis with a proportionally large prepuce in a dog and the use of a preputial shortening procedure for correction of penis-to-prepuce size disparity. Informed consent was obtained from the owners for all aspects of treatment, and contemporary standards of care were provided.

Materials and Methods

Surgical Treatment

The patient was placed under general anesthesia and positioned in dorsal recumbency. The abdominal and preputial areas were clipped and sterilely prepped with a chlorhexidine surgical scrub.

The patient had a proportionally large prepuce preoperatively (Figure 1A). Reconstruction of the prepuce was performed via a hexagonal full thickness preputial excision based on described techniques.^8,9

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A sterile marking pen was used to outline a horizontal elliptical incision along the mid-prepuce, starting approximately 1 cm caudal from the preputial opening and spanning 2 cm wide (Figure 1B). A #12 red rubber catheter was placed in the prepuce, and the penis was palpated and pushed caudally away from the proposed incision. The incision extended 3 cm on either side of the prepuce. The length of resection was chosen based on intraoperative manipulation of the prepuce to match with the size of the penis. The skin incision was created with a #15 blade, and hemostasis was achieved with monopolar electrocautery (Figure 1C).

The subcutaneous tissue was dissected with blunt and sharp dissection and monopolar electrocautery. The cranial aspect of the incision was extended down through the preputial mucosa with tenotomy scissors. Full thickness stay sutures were placed through the proximal portion of the prepuce, the cranial aspect of the mid-prepuce, and the cranial aspect of the distal prepuce (Figure 1D). The caudal aspect of the incision was extended down through the preputial mucosa, and the penis was visualized in the caudal segment of the prepuce (Figure 1E).

A #3 Fr red rubber catheter was placed within the penile urethra. The middle portion of the prepuce was dissected away from the underlying tissue, taking care to preserve the dorsal penile ligament (Figure 1F). The middle portion of the prepuce was removed (Figure 1G). The cranial segment was mobilized caudally until the preputial mucosal edges came in contact (Figure 1H). Stay sutures were placed at the dorsal and ventral aspects of the preputial anastomosis. The preputial mucosa anastomosis was completed with two lines of simple continuous sutures using 4-0 Glycomer 631^a at the dorsal and ventral aspects (Figure 1I). Once complete, the prepuce was retracted, and the penis was visualized to extrude through the preputial opening normally. The surgical site was lavaged with sterile saline. The subcutaneous tissue was closed with an interrupted pattern, and the skin was closed with an intradermal pattern both using 4-0 poliglecaprone 25.^b Following closure, the penis was able to be extruded normally, and catheterization of the penis was normal. The red rubber catheter was removed.

The patient recovered uneventfully from anesthesia. He received meloxicam (0.1 mg/kg subcutaneously once) and methadone (0.2 mg/kg IV once and then q 6 hr as needed) during recovery. An Elizabethan collar was placed on the patient after the operation. The patient was maintained on oral gabapentin (10 mg/kg PO q 8–12 hr) and trazodone (5–10 mg/kg PO q 8–12 hr as needed). He was hospitalized overnight and noted to urinate a consistent stream of normal urine in the hospital. Some blood-tinged urine dripped from the prepuce occasionally, which was considered normal after the operation. Triple antibiotic ointment containing neomycin, bacitracin, and polymyxin was used to coat the incision every 8 hr. He was discharged the next day with gabapentin, trazodone, and oral meloxicam (0.1 mg/kg PO q 24 hr). Chloramphenicol was discontinued at this time. The owner was instructed to monitor for stranguria and dysuria after discharge.

Results

The dog returned 13 days after the operation, and the incision was healing well. The owner reported marked improvement of urine dribbling but not a complete resolution. Urinalysis and urine culture were negative for bacteria. The patient was restarted on phenylpropanolamine and referred to the University of Florida Internal Medicine Service for workup of other causes of incontinence, including ectopic ureter, primary sphincter mechanism incompetence, complications secondary to cryptorchid castration, or primary prostatic disease. Ten weeks after the operation, a CT excretory urogram performed by the Internal Medicine Service revealed a 1 cm prostatic fluid pocket. The ureters emptied into the urinary bladder at the appropriate location, which ruled out an ectopic ureter. It was recommended to continue phenylpropanolamine for possible urethral sphincter mechanism incompetence but was discontinued by the owner. The patient did not return to the University of Florida after this visit.

At 1 yr after the operation, the incision site has healed completely, and the prepuce remained at a reduced length (Figure 2). The owner reported no further UTIs since the surgery. His urination now forms a stream with direction, whereas preoperatively, the urine would dribble down. The dribbling has almost fully resolved, and only occurs just after waking up from sleep or when he becomes excited or afraid. The owner is satisfied with the result of the surgery.

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Discussion

In humans, a diagnosis of micropenis is made when the penile length is smaller than 2.5 standard deviations below the mean penile length of the population.¹ However, in dogs, there is no established criteria. This is because many of the deleterious consequences of this condition in humans are secondary to social or sexual sequelae. In affected canine populations, these effects are negated by elective sterilization and sociological differences between dogs and humans. Thus, clinically significant micropenis in dogs is very rare.

Micropenis in humans is mainly due to sex hormone abnormalities during gestation and early development or in conjunction with other congenital deformities. Penile development is primarily androgen-driven, although human and rodent data suggested estrogen and xenoestrogens may also play a role.^5,9 Micropenis should be differentiated from hypospadia, a more commonly reported penile developmental defect in dogs resulting in a proximal urethral opening. Similar to micropenis, hypospadia is associated with inadequate androgen production.¹⁰ In humans, exogenous estrogen has been shown to target the developing penis in utero to cause hypospadias. Postnatally, a loss of estrogen signaling can also result in a mild hypospadias phenotype. It is unclear whether a direct inference can be made between the information available for hypospadia and our case of micropenis. Interestingly, our patient had potential access to exogenous estrogen through the owner’s cream. Based on existing research in other species, exposure to estrogen may have played a role in our patient’s underdeveloped penis. However, this cannot be definitively determined.

The current treatment for micropenis in humans is testosterone, which includes four doses of 25 mg of testosterone cypionate or enanthate administered intramuscularly once every 3 wks for 3 mo, then repeated as needed. For patients not responsive to testosterone, topical 5-a dihydrotestosterone gel or recombinant human follicle stimulating hormone–luteinizing hormone may be used. It is important for hormone treatment to begin as early as possible, because there is a natural decrease in androgen receptors during the early adulthood period.¹ In canine patients, micropenis is rarely diagnosed early because of the lack of clinical signs and standardized reference size. In our patient, two doses of testosterone were given at around 7 mo of age as a trial treatment for incontinence. We did not observe improvements in his incontinence or micropenis. This may be because of the delay in treatment or inadequate length of treatment. Testosterone may also be ineffective because there is currently no veterinary literature supporting this treatment for micropenis in dogs.

Penile reconstruction surgery with prosthesis is considered in humans only if the patient fails medical treatment because the surgery is associated with high complication rates. Reconstruction surgery is not a treatment option with canine patients because size and appearance are not important considerations. Because micropenis as a sole diagnosis does not cause clinical signs, treatment is not necessary in most animals. In fact, micropenis is likely underreported in dogs when the prepuce is also proportionately small, especially because veterinary patients are frequently neutered at an early age, which decreases endogenous testosterone production. Animals only become clinically affected when the prepuce is significantly larger than the penis, causing urine to pool in the prepuce such as in our patient. A more clinically relevant condition seen in humans is megaprepuce, where there is redundancy of inner preputial skin over a penile shaft and glans of normal shape and size. During urination, there is ballooning and accumulation of urine in the prepuce, which leads to bacteria growth and recurrent UTIs.¹¹ Techniques described for megaprepuce^7,11 are not applicable for use in our patient because they mainly address redundant inner preputial skin, which is not present in our case. The prepuce is likely a normal size in our canine patient, and the cause of micropenis without a proportionally small prepuce cannot be determined.

Preputial shortening was recommended in our patient with a goal of exposing the urethral opening to allow normal micturition. Preputial shortening surgery has been briefly described in textbooks for use with partial penile amputation.⁹ However, there is limited evidence in literature for its clinical use and outcome. We used the described technique with a hexagonal mid-shaft incision and anastomosis with a sliding skin flap. The procedure was feasible and not technically difficult to perform. Our patient urinated well in the immediate postoperative period, whereas the dog in the previous case report could not urinate for 3 days because of swelling and sutures in the preputial ring.⁸ Therefore, it is important to be mindful of the amount of tension applied to the closure to ensure the penis can still move freely in the prepuce and the urethra is not occluded. Although urine dribbling did not resolve immediately after the surgery, the patient improved significantly after 1 yr with minimal dribbling and resolution of recurrent UTIs.

Conclusion

The preputial shortening procedure is feasible and effective for management of dogs with micropenis and size disparity between the penis and the prepuce. Improvement may not be evident in the short-term (approximately 2 mo) recovery period. However, the long-term prognosis for preputial shortening surgery is excellent.

The authors would like to acknowledge Kelly D. Hlubek, BS, MS, for her aid in manuscript preparation and for her aid in obtaining photographs.