Milia are believed to be derived from or to mimic the infundibular portions of a vellus hair follicle. There are several follicular tumors differentiating mainly toward follicular infundibulum or follicular hair bulge of the outer root sheath, such as trichofolliculoma, trichoadenoma, trichoepithelioma, and tumor of follicular infundibulum (TFI). Trichofolliculoma usually presents as a solitary papule or tumor on the head and neck, usually the face. Histologically, there are one or several dilated follicles from which numerous small follicles of varying degrees of maturity radiate. The follicles that branch off the central follicle may in turn give rise to secondary or even tertiary follicles. Trichoadenoma (of Nikolowski) is a rare tumor with hair follicle–like differentiation; it is found as a nodular lesion, particularly on the face and buttocks. Trichoadenoma shows, histopathologically, a well-defined dermal tumor composed of epithelial islands, most of which have a central cystic cavity containing keratinous material. The multilayered squamous epithelium reveals epidermoid keratinization toward the central cavity. Trichoepithelioma is regarded as a poorly differentiated hamartoma of the hair germ. It is composed of branching nests of uniform basaloid cells, sometimes showing peripheral palisading. Its epithelial structures may resemble hair papillae or abortive hair follicles.47
TFI, which was initially reported as a kind of benign adnexal tumor by Mehregan and Butler,48 usually presents as a solitary keratotic papule on the face or scalp of elderly people. Histologically, the tumor shows a plate-like subepidermal epithelial tumor, distinguished from the overlying epidermis by the light staining of its cells and the absence of pigment. The tumor consists of 2 types of cells. The squamous cells, with much lighter staining than those of the epidermis and containing as much periodic acid-schiff-positive material as the outer root sheath, are surrounded by basal cells. Afterward, Ackerman added the distinctive silhouette with a horizontal orientation as one of the crucial findings for the histopathologic diagnosis of TFI.49 Recently, Abbas and Mahalingam50 have reported their own 50 cases of TFI and reviewed 41 reported cases. In their article, they also described a plate-like proliferation of bland epithelial cells extending parallel to the epidermis with multiple epidermal connections as a characteristic finding of TFI.
As we already described, MEP also has 2 histological characteristics other than multiple epidermal cysts, such as a silhouette with a horizontal orientation and branched epithelial structures in connection with epidermal rete ridges. Therefore, these characteristics seem to position MEP close to TFI, although it is difficult to conclude this speculation only by observing the histological slide. Therefore, we finally diagnosed this case as a distinct follicular hamartoma with cystic trichoepitheliomatous features. Further immunohistological study and/or gene analysis may be needed for better understanding the origin of this rare tumor.
1. Berk DR, Bayliss SJ. Milia: a review and classification. J Am Acad Dermatol. 2008;59:1050–1063.
2. Balzer FFC. Miliium confluent retroauriculaires bilateral. Bull Soc Fr Derm Syphilol. 1903;12:361.
3. Hubler WR Jr, Rudolph AH, Kelleher RM. Milia en plaque
. Cutis. 1978;22:67–70.
4. Alsaleh QA, Nanda A, Sharaf A, et al.. Milia en plaque
: a new site. Int J Dermatol. 2000;39:614–615.
5. Combemale P, Faisant M, Dupin M. “Milia en plaque
” in the supraclavicular area. Dermatology. 1995;191:262–263.
6. Cota C, Sinagra J, Donati P, et al.. Milia en plaque
: three new pediatric cases. Pediatr Dermatol. 2009;26:717–720.
7. Fujita H, Iguchi M, Kenmochi Y, et al.. Milia en plaque
on the forehead. J Dermatol. 2008;35:39–41.
8. Ishiura N, Komine M, Kadono T, et al.. A case of milia en plaque
successfully treated with oral etretinate. Br J Dermatol. 2007;157:1287–1289.
9. Samlaska CP, Benson PM. Milia en plaque
. J Am Acad Dermatol. 1989;21:311–313.
10. Stork J. Retroauricular bilateral “milia en plaque
”. Dermatology. 1995;191:260–261.
11. Barzegar M, Mozafari N. A new site of milia en plaque
: report of a case and review of the literature. Int J Dermatol. 2013.
12. Belhadjali H, Youssef M, Yahia S, et al.. Milia en plaque
and discoid lupus erythematosus. Clin Exp Dermatol. 2009;34:e356–e357.
13. Boehm I, Schupp G, Bauer R. Milia en plaque
arising in discoid lupus erythematosus. Br J Dermatol. 1997;137:649–651.
14. Boggio P, Alperovich R, Spiner RE, et al.. Letter: periorbital bilateral milia en plaque
in a female teenager. Dermatol Online J. 2012;18:11.
15. Bridges AG, Lucky AW, Haney G, et al.. Milia en plaque
of the eyelids in childhood: case report and review of the literature. Pediatr Dermatol. 1998;15:282–284.
16. Calabrese P, Pellicano R, Lomuto M, et al.. Milia en plaque
. J Eur Acad Dermatol Venereol. 1999;12:195–196.
17. Cho SH, Cho BK, Kim CW. Milia en plaque
associated with pseudoxanthoma elasticum. J Cutan Pathol. 1997;24:61–63.
18. Dogra S, Kanwar AJ. Milia en plaque
. J Eur Acad Dermatol Venereol. 2005;19:263–264.
19. Dogra S, Kaur I, Handa S. Milia en plaque
in a renal transplant patient: a rare presentation. Int J Dermatol. 2002;41:897–898.
20. Ergin S, Basak P, Sari A. Milia en plaque
. J Eur Acad Dermatol Venereol. 2000;14:47–49.
21. Garcia Sanchez MS, Gomez Centeno P, Rosen E, et al.. Milia en plaque
in a bilateral submandibular distribution. Clin Exp Dermatol. 1998;23:227–229.
22. Hallaji Z, Akhyani M, Jamshidi S, et al.. Bilateral retro-auricular milia en plaque
: a case report and review of the literature. Dermatol Online J. 2010;16:12.
23. Kautz O, Muller S, Braun-Falco M, et al.. Milia en plaque
in a linear pattern. J Eur Acad Dermatol Venereol. 2009;23:1335–1336.
24. Keohane SG, Beveridge GW, Benton EC, et al.. Milia en plaque
–a new site and novel treatment. Clin Exp Dermatol. 1996;21:58–60.
25. Kouba DJ, Owens NM, Mimouni D, et al.. Milia en plaque
: a novel manifestation of chronic cutaneous lupus erythematosus. Br J Dermatol. 2003;149:424–426.
26. Lee DW, Choi SW, Cho BK. Milia en plaque
. J Am Acad Dermatol. 1994;31:107.
27. Lee SH, Kim SC. Linear milia en plaque
on the central face: an acquired skin rash following Blaschko's lines? J Dermatol. 2012;39:936–937.
28. Losada-Campa A, De La Torre-Fraga C, Cruces-Prado M. Milia en plaque
. Br J Dermatol. 1996;134:970–972.
29. Martins LE, Werner B, Fonseca GP. Milia en plaque
. An Bras Dermatol. 2010;85:895–889.
30. Munoz-Martinez R, Santamarina-Albertos A, Sanz-Munoz C, et al.. Milia en plaque
. Actas Dermosifiliogr. 2013;104:638–640.
31. Nambudiri VE, Habib N, Arndt KA, et al.. Milia en plaque
of the nose: report of a case and successful treatment with topical tretinoin. Pediatrics. 2014;133:e1373–e1376.
32. Noto G, Dawber R. Milia en plaque
: treatment with open spray cryosurgery. Acta Derm Venereol. 2001;81:370–371.
33. Pozo J, Castineiras I, Fernandez-Jorge B. Variants of milia successfully treated with CO(2) laser vaporization. J Cosmet Laser Ther. 2010;12:191–194.
34. Quist SR, Franke I, Bonnekoh B, et al.. White papules around the ears: a quiz. Milia en plaque
. Acta Derm Venereol. 2010;90:445–447.
35. Rose RF, Merchant W, Goulden V. Retroauricular milia en plaque
: a rare presentation of lupus erythematosus. Clin Exp Dermatol. 2008;33:715–717.
36. Sandhu K, Gupta S, Handa S. CO2 laser therapy for milia en plaque
. J Dermatolog Treat. 2003;14:253–255.
37. Sharma R, Kumar B. Milia en plaque
. Indian J Dermatol Venereol Leprol. 1995;61:365–366.
38. Stefanidou MP, Panayotides JG, Tosca AD. Milia en plaque
: a case report and review of the literature. Dermatol Surg. 2002;28:291–295.
39. Tenna S, Filoni A, Pagliarello C, et al.. Eyelid milia en plaque
: a treatment challenge with a new CO2 fractional laser. Dermatol Ther. 2014;27:65–67.
40. van Lynden-van Nes AM, der Kinderen DJ. Milia en plaque
successfully treated by dermabrasion. Dermatol Surg. 2005;31:1359–1362, discussion 62.
41. Voth H, Reinhard G. Periocular milia en plaque
successfully treated by erbium: YAG laser ablation. J Cosmet Laser Ther. 2011;13:35–37.
42. Wollina U. Bilateral milia en plaque
of the eyelids: long eyelashes and unibrow–case report and review of literature. Dermatol Surg. 2010;36:406–408.
43. Wong SS, Goh CL. Milia en plaque
. Clin Exp Dermatol. 1999;24:183–185.
44. Zhang RZ, Zhu WY. A new site of milia en plaque
. Indian J Dermatol Venereol Leprol. 2012;78:122.
45. Zhang RZ, Zhu WY. Bilateral milia en plaque
in a 6-year-old Chinese boy. Pediatr Dermatol. 2012;29:504–506.
46. Al-Mutairi N, Joshi A. Bilateral extensive periorbital milia en plaque
treated with electrodesiccation. J Cutan Med Surg. 2006;10:193–196.
47. D. W. Weedon's Skin Pathology. 3rd ed. Londen: Churchill livingstone elsevier; 2010:758–762.
48. Mehregan AH, Butler JD. A tumor of follicular infundibulum
. Report of a case. Arch Dermatol. 1961;83:924–927.
49. Ackerman ABVP, Chongchitnant N. Neoplasms with Follicular Differentiation. Philadelphia, PA: Lea&Febiger; 1993:533.
50. Abbas O, Mahalingam M. Tumor of the follicular infundibulum
: an epidermal reaction pattern? Am J Dermatopathol. 2009;31:626–633.