LY Siu, KW Li, LM Wong, YH Tam

In contrast with the infantile perianal protrusion (IPP) described by Kong¹ which occurs almost exclusively in females, here we reported a unique perianal fibroepithelial polyp (FEP) in a boy.

A healthy boy was born with a 3 cm tubular mass arising from the left side of the anus (Figure 1) and there were no other malformations. As the mass was able to curve up upon stimulation of the scrotal skin and the central dimple could dilate and contract, renal system sonography and magnetic resonance imaging of the lumbosacral spine were performed to rule out aberrant connections before proceeding to surgical excision. Subsequent histopathology analysis revealed that it was a FEP consisting of fibrofatty core and skin adnexae, covered by stratified squamous epithelium and there was no evidence of malignancy. Today, after a follow-up of 8 months, there has been no recurrence.

Figure 1 Tubular mass at the left side of the anus in a newborn baby.

FEP onset during the neonatal period is extremely rare and has been reported predominately in the urethra. Among newborn baby, FEP has never been reported to occur at the perianal region away from the midline. Among adults, FEPs of the anus are relatively common and it is believed that they may represent the result of reactive hyperplasia in response to local irritation or injury.² Physical irritation can possibly lead to localised tissue damage with fibroblastic response and, therefore, polyp formation.

Anzai et al reported that among nine cases in which urethral FEP was diagnosed during the neonatal period, two cases presented with Beckwith-Wiedemann syndrome (BWS).³ They believed that the molecular biological characteristics specific to BWS are related to the rapid enlargement of FEP, which is an inherently benign tumor. Otherwise, FEP of the urethra was believed to arise from developmental error in the invagination process of the glandular material of the inner zone of the prostate.⁴

Differential diagnosis of congenital perianal FEP included eccrine hamartoma⁵ and IPP. Mahdavy et al stated that most authors defined FEPs or acrochordons as polypoid lesions that specifically lacked cutaneous appendages and they reported the first case of congenital eccrine hamartoma present in a perianal region overlying the coccygeal region.⁵ The FEP in our case also had skin adnexae and therefore, it might possibly represent a hamartoma. IPP is characterised by a pyramidal soft-tissue protrusion located in the midline just anterior to the anus, but also can be found posteriorly, or both anterior and posterior.¹ The familial and/or congenital type is related to the constitutional anatomic weakness in the perineum of females but also may represent weakness of the median raphe or perineum.

In conclusion, in our case, the old maxim "it is more common for common diseases to present in uncommon ways at uncommon locations than the uncommon diseases to present in common ways" proves true.

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References

1. Kong AYF. Lump in perineum. Hong Kong Med J 2010;16:317-8.

2. Groisman GM, Polak-Charcon S. Fibroepithelial polyps of the anus: a histologic, immunohistochemical, and ultrastructural study, including comparison with the normal anal subepithelial layer. Am J Surg Pathol 1998;22:70-6.

3. Anzai Y, Koshida S, Yanagi T, Johnin K, Takeuchi Y. Neonatal urethral polyps associated with Beckwith-Wiedemann syndrome. Pediatr Int 2013;55:658-61.

4. Walsh IK, Keane PF, Herron B. Benign urethral polyps. Br J Urol 1993;72:937-8.

5. Mahdavy M, Smoller BR. Eccrine nevus presenting as a perianal skin tag: a case report and review of the literature. Am J Dermatopathol 2002;24:361-3.