Perineal pseudophallus unmasked: a rare case report of lipomatous hamartoma mimicking an accessory penis in an infant

Abstract

Background:

Rare developmental anomalies, distinct from the primary genitalia, can present as phallic-appearing outgrowths in the perineal region.

Case Report:

We report the case of a male infant with a perianal outgrowth resembling an accessory penis, about 3.5 cm long and 1 cm in diameter, phallic-like structure, which underwent surgical excision. Histological examination revealed mature adipose tissue (shaft region), admixed with smooth muscle bundles (Desmin-positive), nerve fibers (S100-positive), and blood vessels (CD34-positive) (glans region).

Discussion:

This case contributes to the limited existing literature by providing comprehensive clinical, radiological, histological, and immunohistochemical correlations, thereby facilitating a deeper understanding and differentiating the lesion from true diphallia or intersex conditions. Our findings underscore the need for multidisciplinary evaluation and thorough histopathological confirmation for accurate diagnosis and management.

Conclusions:

This case highlights the importance of thorough clinical evaluation and histopathological correlation in distinguishing rare congenital soft tissue lesions that may mimic genital anomalies.

Introduction

Perianal or perineal appendages are rare congenital anomalies involving phallic-like structures near the anus or perineum. They differ from a normal penis and are not true accessory genitalia. Instead, they are hamartomatous malformations or residual tissues that mimic the penile shape^[1–3^].

Hamartomas are benign, disorganized tissue growths often found at the site. In the perineal area, they may mimic genital structures, sometimes resembling a pseudophallus or accessory penis. Rarely, they can be mistaken for genital duplication or intersex features^[4–6^]. The differential diagnosis should include perineal lipoma, accessory scrotum, choristoma, teratoma, and genital anomalies related to sexual development disorders. A diagnostic work-up should include ultrasound, MRI to check for communication with pelvic structures and spinal anomalies, along with chromosomal and endocrine assessments in ambiguous cases^[7^]. Surgical excision is a curative treatment often indicated for functional and cosmetic reasons. Histopathological confirmation is essential to differentiate benign lesions from neoplastic or developmental anomalies. While most cases have no functional impact, long-term follow-up may be needed, especially with spinal or urogenital malformations^[7,8^].

HIGHLIGHTS

• This case describes a rare perineal lipomatous hamartoma resembling an accessory penis in an infant.

• Integrated clinical, radiological, histological, and immunohistochemistry correlation has been provided.

• Histopathology confirmed a benign lipomatous hamartoma.

• Simple excision resulted in a cure with an excellent recovery outcome.

Herein, we present a case of a male infant with a lipomatous hamartoma resembling a fully developed penis, including prepuce and shaft-like features. Clinicopathological findings and relevant literature are reviewed. Few cases have been thoroughly characterized through detailed clinical, imaging, histological, and immunohistochemical analysis.

Case report

This case has been reported in accordance with the updated SCARE (Surgical CAse REport) guidelines^[9^].

A 4-month-old male infant with an uneventful antenatal history showed a painless, pedunculated soft tissue outgrowth in the perianal region, resembling a fully formed penis with prepuce, glans, meatus, and fatty shaft, measuring 3.5 cm by 1 cm. Examination revealed no other anomalies.

The infant was born at term following an uneventful pregnancy. Routine antenatal ultrasonography was performed and did not reveal any perineal, urogenital, or spinal abnormalities. The lesion was not detected prenatally, likely due to its small size, superficial perineal location, and lack of associated structural anomalies. Postnatal imaging comprised perineal ultrasonography and pelvic magnetic resonance imaging (MRI). Ultrasonography indicated a superficial, well-defined, predominantly fatty soft-tissue mass devoid of cystic components or internal vascular malformations. MRI identified a pedunculated perineal lesion, consistent with adipose tissue, with no evidence of a urethral tract, corpora cavernosa, corpus spongiosum, or communication with the bladder, urethra, rectum, or spinal cord (Fig. 1).

Figure 1.

Radiological features of the perianal pedunculated phallic-appearing outgrowth resembling an accessory penis. (A) Sagittal T2 WI fat suppression. (B) axial T2 WI revealed: white arrow penis and blue arrow accessory penis.

Surgical excision was performed at 4 months of age to facilitate adequate growth for safe anesthesia, while also minimizing parental anxiety and potential local complications. Under general anesthesia, a circumferential incision was made at the base of the pedunculated lesion. Careful dissection revealed no connection to the urethra, corpora cavernosa, anal sphincter complex, or pelvic structures. The lesion was entirely excised, and the wound was closed primarily. No intraoperative or postoperative complications were observed. Although conservative observation was contemplated, surgical excision was preferred for definitive diagnosis, cosmetic considerations, and to exclude occult communication with deeper structures. Postoperative recovery was smooth, and the patient was discharged on the third day. The patient was monitored postoperatively at 2 weeks, 3 months, and 6 months. Clinical examinations revealed complete wound healing with no indication of residual mass or recurrence.

Gross description

Gross examination revealed a soft tissue outgrowth resembling a phallic structure originating from the perianal region, measuring 5.5 cm in length and 1.5 cm in maximum diameter. The external surface was covered by intact skin, displaying a visible meatus and a non-retracted, redundant prepuce fused to the underlying tissue. Upon sectioning, the lesion demonstrated heterogeneity, with yellow areas consistent with adipose tissue (shaft region) and grayish-white, soft-textured regions (glans). No identifiable corpus spongiosum, corpora cavernosa, or urethral structure was observed (Fig. 2).

Figure 2.

Gross features of the perianal pedunculated phallic-appearing outgrowth resembling an accessory penis. Grossly, there is a phallic-like soft tissue outgrowth in the perianal region, measuring 3.5 cm in length and 1 cm in maximum diameter with a prepuce and meatus. The external surface was covered by intact skin with a non-retracted prepuce. The foreskin was redundant and fused to the underlying tissues. Upon sectioning, heterogeneous yellow (fatty tissue) areas are intermixed with grayish-white areas of soft consistency. There is no corpus spongiosum or bilateral corpora cavernosa. There is no urethra.

Histological features of a perianal, pedunculated, phallic-appearing outgrowth resembling an accessory penis

The shaft was covered by unremarkable epidermis overlying a dermis and subcutis with heterogeneous tissue elements. The papillary and mid-dermis contained abundant smooth muscle bundles (star). Fibrous septa separated multiple lobules of uniform mature adipocytes (thick arrow) in the deep dermis and subcutis, characterized by clear cytoplasm and small nuclei. Small- to medium-sized blood vessels with various wall thicknesses (thin arrow), nerve fibers, and fibroblasts were present within the adipose tissue (Fig. 3, Panels A–F). The glans region primarily consisted of mature fibroconnective tissue, containing nerve fibers (double-headed arrow) and blood vessels (Fig. 3, Panels G–I). No cellular atypia, lipoblasts, necrosis, or increased mitosis was observed, supporting a benign diagnosis.

Figure 3.

Histological features of a perianal, pedunculated, phallic-appearing outgrowth resembling an accessory penis. (A–F) The shaft of phallic-appearing outgrowth consists of unremarkable epidermis, overlying a dermis and subcutis with heterogeneous tissue components. The papillary and mid-dermis exhibit abundant, haphazardly arranged bundles of smooth muscle fibers (star). In the deep dermis and subcutaneous tissue, several areas are composed predominantly of mature adipocytes arranged in lobules (thick arrow), separated by broad fibrous septa. The adipocytes are uniform in size and shape, with clear cytoplasm reflecting dissolved lipid content and small, eccentrically located nuclei. Interspersed within these adipose lobules are small to medium caliber blood vessels with both thin and thick walls (thin arrow), as well as a few nerve fibers and scattered fibroblasts. (G–I) The glans of phallic-appearing outgrowth consists mainly of mature fibroconnective tissue, admixed with variably sized neural (double-headed arrow) and vascular elements. No evidence of cellular atypia, lipoblasts, necrosis, or increased mitotic activity is observed, supporting the benign nature of the lesion. Magnifications: A: × 20; B: × 100; C: × 40; D: × 20; E: × 100; F: × 200; G: × 40; H: × 100; I: × 200.

Immunohistochemical features of perianal phallic-appearing outgrowth

Desmin immunostaining showed a thick layer of smooth muscle fibers in the mid-dermis, with muscle bundles arranged haphazardly in the deep dermis extending into adipose lobules (Fig. 4, Panels A–C). The glans exhibited irregular nerve bundles that were positive for S100 (thick arrow) and intermingled with CD34-positive blood vessels (double arrow) (Fig. 4, Panels D–I). These findings confirmed the lesion’s complex hamartomatous nature, consistent with a lipomatous hamartoma resembling an accessory penis (Fig. 4).

Figure 4.

Immunohistochemical features of a perianal, pedunculated, phallic-appearing outgrowth resembling an accessory penis. (A–C) The shaft of phallic-appearing outgrowth. Desmin immunostaining (thin arrow) highlights a thick, band-like layer of thin smooth muscle fibers within the mid-dermis. In the deep dermis, these muscle fibers are haphazardly arranged in multiple directions, with some bundles extending into the underlying adipose lobules. (D–I) The glans of a phallic-appearing outgrowth. There are irregularly oriented nerve bundles, which are positive for S100 (thick arrow), intermingled with CD34-positive blood vessels (double arrow). These findings further support the complex hamartomatous composition of this benign, accessory-like phallic structure (lipomatous hamartoma). Magnifications: A: × 20; B: × 20; C: × 40; D: × 20; E: × 100; F: × 100; G: × 40; H: × 100; I: × 200.

Discussion

A few reports describe hamartomatous or lipomatous lesions presenting as pseudophallus, accessory penile-like structures, or scrotum-like masses^[2,3,7,8^]. Approximately 50 cases of congenital perianal lipomas have been recorded^[4–8^]. Perineal hamartomas are rare benign lesions with disorganized proliferation of mature tissue native to the area, sometimes mimicking male genitalia and causing diagnostic confusion with true genital duplication or intersex conditions. Our findings align with previous clinicopathological reports^[2,10^]. The differential diagnosis included sacrococcygeal teratoma, accessory phallus, lipoblastoma, and other soft tissue tumors. Perineal hamartomas and lipomas are often associated with urogenital and anorectal malformations in neonates, presenting as accessory scrotum, penoscrotal pseudoduplication, or lipomatous growths^[2,3,11^]. They frequently accompany cryptorchidism, imperforate anus, and labioscrotal malformations^[10^]. We report a rare case of lipomatous hamartoma in the perianal area mimicking a phallic structure in an otherwise healthy male newborn. Few cases with detailed clinical, imaging, histological, and immunohistochemical data have been documented.

Diagnostic tools are vital for identifying and characterizing perineal masses, such as perineal development syndrome (PDS) and accessory scrotum. Ultrasound is the first-line imaging modality for differentiating solid from cystic masses and providing initial anatomical information. Prenatal diagnosis with ultrasound is possible in some cases^[2^]. For detailed anatomy, MRI is preferred during preoperative evaluation^[11^], providing precise boundaries, location, and relationships with pelvic organs and the spine, as well as assessing internal anomalies such as bladder, urethral, kidney, colon, and rectosigmoid duplications^[10^]. MRI also characterizes suspected sacrococcygeal teratomas by signal differences on T1 and T2 images^[11^]. Computed tomography urography is useful for evaluating associated internal anomalies before surgery^[10^]. In some cases, voiding cystourethrography may be used to visualize the urethras and detect any vesicoureteral reflux^[10^]. Histopathological examination of the excised tissue is essential for definitive diagnosis^[11^]. This enables the accurate characterization of the lesion and differentiation between various types of perineal masses, such as hamartomas, lipomas, and more concerning entities, including rhabdomyosarcomas^[12^].

Perineal masses like pseudodiphallia and accessory scrotum are usually treated with surgical excision. Excess penile tissue in pseudodiphallia is often removed along with foreskin circumcision^[10^]. Complete removal is recommended for accessory scrotum with lipoma or hamartoma^[2^]. The surgical approach varies based on presentation and anomalies. Complex cases with anorectal malformations may require staged procedures, starting with colostomy and followed by repair^[11^]. Surgeries are often done in early infancy or childhood, sometimes within days of birth^[11^].

Histopathological examination is key to diagnosing perineal masses. Accessory penile-like tissue usually lacks the normal penile structure in pseudodiphallia. Histology often reveals mature adipose tissue with fibrous septa, vessels, and nerve trunks in perineal lipomas or hamartomas, which may be associated with an accessory scrotum^[10^]. The scrotal-like part may contain numerous muscle bundles in fibrous tissue, with skin that includes sebaceous glands and hair follicles^[3^]. In fibrous hamartoma of infancy, an entity that can occur in genital areas, the histology shows myofibroblast fascicles, disorganized mature adipocytes, and primitive mesenchymal cells^[12^]. These may also include smooth muscle fibers, neural tissue, and blood vessels within adipose tissue^[2^]. Lipomatous hamartomas often develop through dysregulated embryonic growth pathways, such as mTOR or Shh, causing focal overgrowth of mature tissues. These are often driven by PTEN inactivation, leading to uncontrolled adipocyte growth in benign HAs. Chromosomal rearrangements involving HMGA2 at 12q15, common in benign lipomatous tumors, also contribute to abnormal mesenchymal proliferation. Histopathological examination is essential not only for diagnosis but also for ruling out more aggressive lesions, such as infantile fibromatosis or rhabdomyosarcoma [^[12^].

Follow-up is essential for monitoring complications and evaluating outcomes. Patients are assessed for wound healing, urinary, and erectile function. Most recover without issues, such as infection, hematoma, or wound dehiscence^[10^]. Long-term follow-up, lasting up to 6 months, aims to ensure optimal cosmetic and functional results^[10^]. Outcomes are more challenging to predict in complex cases with multiple anomalies, and patients may require ongoing management of urinary and bowel issues^[11^]. While most cases are cured by local excision, there’s a small risk of recurrence, requiring continued follow-up^[10,11^].

The rarity of these conditions leads to few reported cases, making it hard to determine their causes and the best treatments. Most reports are based on small studies, which may not accurately reflect all presentations or outcomes, and some cases lack long-term follow-up, thereby limiting our understanding of their progression and complications. Still, most infant perineal masses are benign and treatable with surgery. This case enhances knowledge by providing a rare, well-documented example of a pseudophallus caused by a lipomatous hamartoma, supported by multimodal imaging and immunohistochemistry (Desmin, S100, CD34). It demonstrates structural mimicry of penile features, lacking urethral or erectile tissue, thereby highlighting diagnostic challenges. The report stresses the importance of correct diagnosis, as misdiagnosis as true diphallia or sex development disorder could lead to unnecessary tests and parental anxiety. By emphasizing the benign nature and simple surgical treatment, this case helps clinicians and reassures families.

Conclusion

This report describes a male newborn with a benign perineal pseudophallus, histopathologically confirmed as a lipomatous hamartoma. Accurate diagnosis is crucial to distinguish such lesions from sexual development disorders. Surgical excision is the preferred treatment and is generally effective. Careful planning is essential, especially for lesions near sphincter muscles or those associated with anorectal anomalies. The case highlights the importance of considering lipomatous hamartomas in the differential diagnosis of perineal masses in newborns, as they can mimic genital anomalies and cause parental concern. Confirmatory histopathology guides treatment and provides reassurance to patients.

Ethical approval

The study was approved by the Ethics Committee of the Armed Forces Hospital Southern Region (protocol code: AFHSRMREC/2025/UROLOGY/816, dated August 3, 2025).

Consent

Written informed consent was obtained from the patient’s parents for publication and any accompanying images, and the study was approved by the Institutional Review Board. A copy of the written consent is available for review by the Editor-in-Chief of this journal upon request.

Sources of funding

None.

Author contributions

M.H.: protocol development, manuscript writing, manuscript review., Y.A.: protocol development, manuscript writing, manuscript review., S.A.A.: data collection and manuscript review. O.S.: protocol development, manuscript writing, editing, manuscript review, and senior author., M.F.B.: data collection and manuscript review. M.R.H.: data collection and manuscript review.

Conflicts of interest disclosure

The authors whose names are listed immediately below certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Omar Safar.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Data availability statement

The data supporting this study’s findings are available from the corresponding author upon reasonable request.

Competing interests

The authors declare no competing interests.