Recurrent secondary milia after full-thickness skin graft using retroauricular donor skin for dog-bite defect: a case report

Min Wook Kim; Chang Ryeol Keum; Kwang Sik Seo; Jung Yeol Seo

doi:10.7181/acfs.2025.0082

Abstract

Full-thickness skin grafting (FTSG) is frequently used to reconstruct facial soft tissue defects because it provides favorable color and texture matching. Secondary cystic lesions, including milia or epidermal cysts, that develop after FTSG are rare. A 29-year-old woman sustained a dog-bite injury resulting in a 4.5× 2.5 cm defect involving the philtrum and upper lip. The philtrum was reconstructed using a full-thickness skin graft harvested from the retroauricular area, while the upper lip was repaired using a mucosal V-Y advancement flap. Ten months later, hypertrophic scarring developed, and a second FTSG was performed using contralateral retroauricular skin. Despite repeated intralesional triamcinolone injections, the grafted area became tender and pruritic, with the appearance of multiple milia-like lesions. Over the subsequent 9 months, three recurrent cystic nodules developed within the scar tissue and were serially excised. Histopathological examination confirmed the diagnosis of secondary milia. After complete excision, no recurrence was observed for over 3 years. We discuss possible contributing mechanisms, including adnexal survival within grafts and the role of remnant epidermis or ductal obstruction. Awareness of this complication may help guide donor-site selection and wound-bed preparation in perioral reconstruction.

Keywords: Case reports / Epidermal cyst / Lip / Philtrum / Postoperative complications / Skin transplantation

Abbreviations

FTSG

full-thickness skin grafting

INTRODUCTION

Secondary epidermal cysts and milia are benign epithelial lesions that occasionally develop following trauma, burns, or reconstructive surgery. These lesions arise from epidermal cells or adnexal structures implanted within the dermis, leading to the formation of cystic cavities lined with keratinizing squamous epithelium. Although milia are known to occur after dermabrasion and split-thickness skin grafting, their development following full-thickness skin grafting (FTSG) is uncommon. We report a rare case of recurrent secondary milia that developed within the philtral scar after sequential FTSG procedures using retroauricular skin for reconstruction of a philtrum defect caused by a dog-bite injury. To the best of our knowledge, recurrent cystic lesions occurring specifically on the philtrum after FTSG have rarely been described, histologically confirmed, and successfully treated with complete excision.

CASE REPORT

A 29-year-old woman presented with a traumatic defect involving the philtrum and upper lip after being bitten by her pet Jin-do dog. She was evaluated 5 days after the injury. The defect measured 4.5×2.5 cm and exposed the subcutaneous tissue and a portion of the orbicularis oris muscle. The wound margins were irregular and partially epithelialized. During surgery, the irregular wound bed was curetted, and the margins were sharply debrided to expose a uniform wound surface. The philtrum was reconstructed using a full-thickness skin graft harvested from the right retroauricular area and the upper lip defect was repaired using a mucosal V-Y advancement flap. The graft healed well, with full take (Fig. 1).

Approximately 10 months later, a hypertrophic scar developed on the philtrum, accompanied by mild contracture and pruritus. Scar revision was performed using another full-thickness skin graft harvested from the contralateral retroauricular area (Fig. 2). Healing remained uneventful. Three months after the revision, the patient noticed the development of white papules associated with tenderness within the grafted area. Intralesional triamcinolone acetonide injections were administered three times at monthly intervals; however, the number of lesions gradually increased. On examination, the grafted skin showed multiple firm, whitish papules measuring 4–6 mm in diameter, with an appearance consistent with milia. The lesions were excised under local anesthesia. The excised specimens consisted of firm keratinous nodules. Histopathological findings showed a keratin-filled dermal cyst lined with stratified squamous epithelium, confirming the diagnosis of secondary milia (Fig. 3).

Over the following 9 months, the patient experienced two additional recurrences at approximately 3-month intervals. Each recurrence was treated with surgical excision, and histopathological analysis again confirmed milia (Fig. 4, Supplementary Fig. 1). After the third excision, the scar remained soft, flat, and stable, with no evidence of recurrence for more than 3 years (Fig. 5). The patient’s symptoms, including pruritus and pain, resolved completely.

DISCUSSION

Secondary milia are keratin-filled cysts that may arise after trauma, inflammation, or reconstructive surgery [1,2]. Although they are well described after dermabrasion and burns, their occurrence after FTSG is uncommon (Table 1) [3-7]. This case illustrates an unusual pattern of recurrent milia developing within grafted skin after sequential FTSG procedures using retroauricular donor skin. Only isolated cases have described similar phenomena. Lee et al. [8] reported milia formation following facial resurfacing procedures. However, recurrent cystic lesions developing specifically after retroauricular FTSG for philtrum reconstruction have not been previously documented. Accordingly, this case provides insight into potential graft- and recipient-site factors contributing to the development of secondary milia.

Retroauricular skin is preferred in facial reconstruction because of its favorable color and texture match. However, the retroauricular region has been described as an adnexa-rich or se-baceous-associated area in dermatological classification studies [9-11]. Because FTSG includes the entire dermis, it inherently transfers sebaceous glands, hair follicles, and eccrine ducts, some of which may survive revascularization. When sebaceousrich graft tissue is transplanted into a recipient site with a different adnexal composition, distortion or obstruction of pilosebaceous ducts may occur, leading to impaired keratin outflow and cyst formation. This process may predispose to keratin accumulation and subsequent secondary milia formation. Although milia are typically sporadic complications of FTSG, donor-site characteristics may have contributed to the development of cystic lesions in this patient.

The patient’s injury resulted from a dog bite, which typically produces irregular wounds with uneven depth. In this case, partial epithelialization was observed in peripheral zones before surgery. Although these areas were curetted, microscopic epidermal remnants may have remained embedded within the wound bed and could have contributed to implantation cyst formation once the graft matured. This mechanism may explain the recurrence despite sequential excisions. These observations highlight the importance of allowing adequate demarcation of traumatic wounds and considering complete excision of epithelialized margins, rather than curettage alone, when preparing the wound bed for grafting.

Following the first FTSG, a hypertrophic scar developed at the grafted philtrum. This condition is characterized by excessive fibroblast activity, increased collagen deposition, and elevated tissue tension. Such structural changes may generate compression or angulation of pilosebaceous ducts, leading to obstruction of glandular outflow. Therefore, the combination of sebaceousrich graft tissue and recipient-site fibrosis may have created a microenvironment favorable for recurrent cyst formation.

Taken together, the recurrent milia observed in this patient likely resulted from multiple interacting mechanisms, including high adnexal density in the donor skin, microscopic epidermal remnants from the initial injury, hypertrophic scarring, and mechanical tension related to dynamic perioral movement. The simultaneous presence of these factors may account for the unusual recurrence of cystic lesions, despite appropriate graft take and otherwise uneventful wound healing. This case underscores several practical considerations for reconstruction of traumatic defects. In irregular bite wounds, complete removal of epithelial remnants through sharp excision may help reduce the risk of milia formation. Donor-site selection may take into account differences in adnexal density, particularly when reconstructing areas with relatively fewer sebaceous glands. Longterm monitoring is recommended, as secondary milia may develop months after grafting, especially in areas prone to scarring or inflammation. Complete surgical excision remains the definitive treatment for established cystic lesions.

Recurrent secondary milia after FTSG are rare but possible complications. In this case, both donor- and recipient-site factors likely contributed to repeated lesion formation. Awareness of these mechanisms may assist surgeons in optimizing woundbed preparation and graft selection to minimize the risk of postoperative cyst formation.

Notes

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Ethical approval

This report was reviewed and approved for exemption from informed consent by the Institutional Review Board of Pusan National University Yangsan Hospital (IRB No. 55-2025-147), as it is a retrospective case report without identifiable personal information.

Patient consent

The patient provided written informed consent for the publication of the case and related images.

Author contributions

Conceptualization: Min Wook Kim, Jung Yeol Seo. Data curation: Min Wook Kim, Chang Ryeol Keum. Formal analysis: Min Wook Kim, Chang Ryeol Keum. Project administration: Kwang Sik Seo. Resources: Kwang Sik Seo. Supervision: Jung Yeol Seo, Kwang Sik Seo. Validation: Min Wook Kim, Jung Yeol Seo. Writing–original draft: Chang Ryeol Keum. Writing–review & editing: all authors. All authors read and approved the final manuscript.

Supplementary materials

Supplemental data can be found at: https://doi.org/10.7181/acfs.2025.0082.

Supplementary Fig. 1.

Secondary recurrence of milia within the grafted scar. Despite prior excision, recurrent milia-like cystic lesions developed again within the grafted area. Repeat excision was performed, demonstrating similar gross and histological features of secondary milia (hematoxylin and eosin stain, ×40).

acfs-2025-0082-Supplementary-Fig-1.pdf

Fig. 1.

A 29-year-old woman with a defect of the philtrum and upper lip caused by a dog bite. (A) Initial presentation of the wound with irregular margins and partial epithelialization. (B) Immediately postoperative photograph after reconstruction with a full-thickness skin graft from the right retroauricular region combined with an oral mucosal V-Y advancement flap.

Fig. 2.

Revision surgery for hypertrophic scarring. Approximately 10 months after the initial reconstruction, a hypertrophic scar developed at the grafted philtrum, accompanied by mild contracture and pruritus. Scar revision was performed using a second full-thickness skin graft harvested from the contralateral retroauricular region.

Fig. 3.

First occurrence of milia after full-thickness skin graft. After the revision surgery, multiple papules developed within the grafted philtrum, consistent with milia-like cystic lesions. Surgical excision was performed, and histopathological examination demonstrated cysts consistent with secondary milia (hematoxylin and eosin stain, ×40).

Fig. 4.

Third recurrence and repeated surgical excision. A third recurrence of cystic lesions occurred approximately 3 months after the second excision. Complete excision was again performed, and histopathological findings remained consistent with secondary milia (hematoxylin and eosin stain, ×40).

Fig. 5.

Long-term postoperative outcome. Long-term follow-up photograph obtained 3 years after the final excision shows a stable, flat scar on the philtrum without recurrence of milia or cystic lesions.

Table 1.

Reported cystic complications in scarred or grafted skin

Author (year)	Location of lesion	Procedure/context	Interval (mo)	Recurrence	Treatment
Park et al. (2016) [3]	Wrist	Carpal tunnel release	Approximately 20	No	Excision
Kim et al. (2011) [4]	Nasolabial fold	Autologous fat injection	Approximately 6	No	Excision
Diniz et al. (2020) [5]	Cheek, malar area	Post-trauma epidermal cyst	Approximately 6	No	Excision
Tandon et al. (2015) [6]	Periorbital	Post-trauma epidermoid cyst	Approximately 6	No	Excision
Monnet et al. (2022) [7]	Lip	Fat graft	Approximately 3	No	Excision
Present case	Philtrum (upper lip)	Full-thickness skin grafts × 2	Approximately 3	Yes (× 3)	Serial excision

REFERENCES

1. Berk DR, Bayliss SJ. Milia: a review and classification. J Am Acad Dermatol 2008;59:1050-63.

2. Han SW, Kim J, Kim SW, Eom M, Yang CE. Intramuscular epidermal cyst in the masticator space: a case report. Arch Craniofac Surg 2023;24:193-7.

3. Park HY, Sur YJ, Kim YV. Epidermal inclusion cyst after carpal tunnel release: a case report. J Wrist Surg 2016;5:67-70.

4. Kim HI, Hwang SM, Song JK, Lim KR, Jung YH, Ahn SM. Epidermal inclusion cyst after fat injection: a case report. Arch Aesthetic Plast Surg 2011;17:181-3.

5. Diniz DA, Mendonca TL, Pinto PS, Souza Junior FA, Barros AV, Nascimento VH. Post-traumatic epidermal cyst of the face: case report. Res Soc Dev 2020;9:e77849190.

6. Tandon P, Saluja H, Sachdeva S, Dadhich A. Epidermoid cyst over periorbital region: case report. Pravara Med Rev 2015;7:21-3.

7. Monnet P, Bagot M, Rivet J, Roux J, Petit A, Al-Hage J. Epidermal cyst formation of the lip following autologous fat transplant. JAAD Case Rep 2022;26:101-3.

8. Lee HW, Kim CG, Song JS, Koh IC, Kim H, Kim KN. Management of epidermal cysts arising from scar tissues: a retrospective clinical study. Medicine (Baltimore) 2018;97:e12188.

9. Kim YS, Park JJ, Yi HS, Park JH, Kim HI. Is the retroauricular region a suitable donor site for full-thickness skin grafting in the era of mask wearing? Arch Craniofac Surg 2023;24:66-72.

10. Grice EA, Segre JA. The skin microbiome. Nat Rev Microbiol 2011;9:244-53.

11. Kim JH, Ahn CH, Kim S, Lee Y, Oh SH. Comparative measurement of biophysical parameters in consideration of skin graft donor site for nasal defects. Ann Dermatol 2019;31:1-5.