Pubic Aneurysmal Bone Cyst Following Penile Inversion Vaginoplasty: A Case Report

 

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Aneurysmal bone cysts (ABCs) are aggressively expansile, multiloculated vascular lesions that usually present in children and adolescents with a slight female predominance.¹ They can be locally destructive, causing clinical symptoms such as pain, swelling, inflammation, pathological fractures, neurological impartments, joint and growth plate disruption, and longitudinal or angular deformities of the extremities. The exact etiology of ABCs is currently unknown and hypothesized to be related to vascular malformations or disruption of osseous vascularity.

ABCs are rare entities with an annual incidence of 1 in a million individuals and represent 1% to 6% of all primary bone tumors.² The most commonly affected locations are the metaphysis of long bones (67%), posterior elements of the spine (15%), and the pelvis (9%). Notably, ABCs involving the pubic bone are even more rare.³  

Given the destructive nature of ABCs and their very rare probability of malignant transformation, treatment is typically directed at complete surgical curettage and/or excision while preserving vital anatomic structures and overall functional status. This intervention can be particularly challenging when managing pelvic lesions. Additionally, there have been no reports describing the development of pubic ABCs following penile inversion vaginoplasty (PIV), a gender-affirming operation designed to rearrange penoscrotal structures into a sensate and functional vagina. In this case report, we discuss the unique presentation and successful treatment of a pubic ABC in a patient who recently underwent PIV.

A 37-year-old transgender female was initially referred to the orthopedic oncology clinic for evaluation of a 12-month history of left hip and groin pain. She had undergone gender-affirming PIV about 19 months prior to presentation. Her medical history included gastroesophageal reflux disease and anxiety. She continued to receive weekly injections of estrogen. Physical examination demonstrated a mild antalgic gait without crepitation or joint subluxation. She had fullness and tenderness to palpation over the pubic symphysis without surrounding skin changes or adjacent lymphadenopathy, and bilateral lower extremities exhibited normal motor and sensory findings. 

A pelvic radiograph revealed evidence of a destructive mass mostly involving the left superior pubic ramus. Magnetic resonance imaging (MRI) with contrast revealed a low T1 signal intensity and heterogenous T2 hyperintensity 7.5 × 4.9 × 4.3-cm destructive mass in the left superior pubic ramus extending across the pubic symphysis into the right superior pubic ramus with some evidence of fluid-fluid levels (Figure 1). These findings did not definitively rule out malignancy. A needle core bone biopsy demonstrated a variably cellular spindle and round lesion with islands of osteoid formation and focal necrosis. The cells were negative for CD34, S100, and desmin. There was no evidence suggesting osteosarcoma, and final review favored the diagnosis of an ABC. Given the highly destructive nature of the mass, operative resection and curettage was recommended. A multidisciplinary team consisting of orthopedic oncology, plastic surgery, surgical oncology, and urology was assembled to perform the operation.

Figure 1. Preoperative axial T2-weighted MRI delineating the pubic bone lesion.

During the operation, a transverse incision was utilized to dissect down to bilateral pubic rami and the symphysis. The attachments of the rectus abdominis muscle were divided from the pubis, and neurovascular structures were carefully preserved while dissecting the tumor. Four bone cuts involving bilateral superior and inferior pubic rami were designed under fluoroscopic guidance and performed successfully without disrupting the adjacent joints (Figure 2). The resected bone and tumor specimen was sent fresh to pathology for analysis. The bladder, prostate, and urethra were carefully visualized and appeared uninjured. To reconstruct the residual 10 × 15-cm defect, a biologic dermal mesh (XenMatrix) was shaped to serve as an underlay at the lateral defect and a bridge in the central portion. The mesh was secured to the rectus muscles superiorly, pubic fascia inferiorly, and inguinal fascia laterally. 

Postoperatively, the patient had an uncomplicated, self-resolving ileus and otherwise unremarkable hospital course. She was discharged after 4 days of hospitalization. The final pathology report confirmed the diagnosis of a solid ABC with negative margins. She was most recently seen in clinic 14 months postoperatively with no recurrence of symptoms or of the mass as indicated by repeat contrast MRI (Figure 3).

Figure 2. Pelvic radiograph taken 1 month postoperatively demonstrating the boundaries of the surgical resection. Bilateral superior pubic rami and pubic symphysis were resected with preservation of the sacroiliac and hip joints.

Figure 3. Axial T2-weighted MRI taken 14 months postoperatively showing no evidence of recurrent or residual tumor.

In this report, we describe the development and treatment of a pubic ABC in a patient who had undergone uncomplicated robotically assisted PIV almost 2 years prior to presentation. Our patient began developing unilateral pain—a common symptom associated with ABCs—about 7 months postoperatively, with imaging demonstrating an osteolytic pubic bone mass. Accurate diagnosis was achieved by performing a needle core biopsy, and histological analysis revealed blood-filled spaces enmeshed in a myxocollagenous, trabeculated stroma. Treatment typically involves curettage or direct excision, the latter of which was performed in our patient due to size and concern for possible osteosarcoma. Although surgical excision of pelvic ABCs carries significant potential morbidity, the operation was performed successfully with minimal early or late complications in our patient, who was followed for over 14 months. 

ABCs can be primary or secondary if found to be arising from a different type of primary tumor. Given our patient’s relatively healthy medical history, we hypothesize that she had developed a primary ABC. Additionally, the most common primary lesions associated with secondary ABCs are giant cell tumors and chondroblastomas,⁴ but final pathological analysis of the entire surgical specimen did not reveal any features resembling masses other than an ABC. The etiology of both primary or secondary ABCs is hypothesized to be related to vascular malformations in the bone. Recent studies suggest that secondary ABCs may be related to factors such as hyperemia and dilatation of the vascular bed⁵ or arteriovenous malformations of primary lesions⁶ leading to increased pressure and expansion within the bone itself, causing a cycle of erosion and resorption.⁷  

The development of a pubic ABC following PIV is particularly interesting, as this unique presentation has not yet been described in the literature. During PIV, the neovaginal space is carefully developed along the rectoprostatic (Denonvilliers) fascia, avoiding injury to the rectum, bladder, urethra, and prostate gland.⁸ The dissection ends when the peritoneal reflection is encountered to avoid entering the abdominal cavity. The component separation of the penis is performed by degloving the shaft, separating and shortening the urethra, and removing the corpus cavernosum from the dorsal fascia while preserving the neurovascular bundle to the glans, which is shaped into the neoclitoris. A bilateral orchiectomy is performed while preserving the ilioinguinal nerves. The neovaginal canal is lined with a superiorly based, tubularized, and inverted penile skin flap supplemented with scrotal skin grafts. The neoclitoris and urethra are delivered through the penile skin flap prior to the final inset.⁸

The pubic bone is nourished by branches of the external and internal iliac arteries. Many steps during a PIV result in disruption of native blood supply to the pubic bone and reliance on vascular rerouting through collateral circulation. Such notable steps include excision of ischiocavernosus and bulbospongiosus muscles, cauterization of bilateral cavernosal arteries at the proximal root of the corpora cavernosum, elevation of the penile flap to the level of the pubic symphysis, undermining of the mons pubis and perineal flaps, and elevation of a peritoneal flap centered on the rectoprostatic fascia.^8,9 This level of vascular disruption is typically inconsequential as demonstrated by low rates (1%) of soft tissue or bony necrosis.¹⁰ Furthermore, although vaginal bleeding is a common postoperative finding, only 0.3% to 5% of patients require reoperation to control ongoing bleeding, with the typical source of hemorrhage arising from the corpus spongiosum.^11,12 

Given the relationship between ABCs and abnormal bony vascularity, our primary hypothesis is that disruption of iliac arterial branches during PIV resulted in subclinical vascular malformations affecting the pubic bone of our patient. One other case report documents a prostatic artery pseudoaneurysm diagnosed on postoperative day 26 following PIV in a 46-year-old patient presenting with hemorrhagic shock,¹³ suggesting the rare possibility of PIV to cause other subclinical vascular complications involving branches of the iliac arteries. Importantly, it is worthwhile to consider the possibility of a genetic predisposition to ABCs, which have been proposed to be true neoplasms with connection to chromosomal aberrations;^14,15 however, we are unable to prove this without formal genetic testing.

Although it is impossible to distinguish coincidence from causation in this case, the patient’s recency of surgery and development of a rare ABC in a nearby bone warrants the speculation and discussion provided in this report. Given that it is exceedingly rare for PIVs to cause vascular or orthopedic complications, one possible explanation is that the patient had an undiagnosed genetic predisposition to developing an ABC, which was locally precipitated in the pubic bone due to vascular disruptions caused by the PIV. Nevertheless, practitioners should be aware of this very rare complication in future patients undergoing PIV.