A retrospective investigation of twenty-ve cases with periocular pilomatrixoma

Purpose Pilomatrixoma is an uncommon benign skin tumor, developing from hair follicle matrix. It consistently presents in the head and neck region patients with pediatric predominance, from infancy to senior. Thus far, few case series studies have been focused on the periocular lesions that involve the eyelid and eyebrow. In the present study, we carried out a case series with 25 patients of periocular pilomatrixoma. Methods Records from the Hospital Information System (HIS) of our hospital were reviewed retrospectively between the years 2009 and 2020 to search for all patients that were diagnosed as pilomatrixoma of eyelid or eyebrow. All patients received excision in the Department of Ophthalmology and histological examinations in the Department of Pathology. Patients’ information and characterization of tumors features were recorded and analyzed.


Introduction
Pilomatrixoma, a rare hair follicle matrix-derived benign tumor, always presents in the head and neck in pediatric populations [1]. In 1880, Malherbe and Chenantais rst described it as "calcifying epithelioma of Malherbe". In 1949, Lever and Griesemer found the calcifying epithelioma arising from immature hair matrix cells [2]. In 1961, Forbis and Helwig used the term "pilomatrixoma" instead of previous "calcifying epithelioma" since they noticed the tumor developing from primitive epidermal germ cells that are differentiating toward hair matrix cells [3].
With the incidence of around 1% among benign skin lesions [4], pilomatrixoma is an uncommon lesion that presents at periocular regions, such as eyelid and eyebrow. Clinically, the diagnosis of periocular pilomatrixoma is somehow di cult given the similarity of their appearance to other dermal masses, such as chalazion [5,6]. Therefore, histological examinations upon complete surgical resection are essential for the con rmation of such conditions [1].
Till now, most of the periocular pilomatrixoma are reported as case reports around the world. In English literatures, we noticed that two case series investigations of more than 10 patients have been reported in Israel [7,8]. Another study of 13 cases of pilomatrixoma of the ocular adnexae was reported in German [9].
In the present study, we aimed for the rst time to present a relatively large case series of periocular pilomatrixoma from one ophthalmic clinic in order to show the clinical and histopathological  Table 1.  Table 1). The CT (computerized tomography) scan under nonenhanced mode indicated that all lesions were well-circumscribed with calci cation (Fig. 1).
The follow-up histopathological observations con rmed the diagnosis of pilomatrixoma. All the tumors were composed of typical basophilic cells in the peripheral and shadow cells in the center ( Fig. 2A). Meanwhile, calci cations (Fig. 2B) were found in 23 cases (92 %) and foreign body giant cells (Fig. 2C) were detected in 18 cases (78 %) ( Table 1).
All the patients received complete excision in the Department of Ophthalmology of our hospital. No intraoperative or postoperative complications was occurred. Moreover, no recurrence or malignant transformations were observed upon follow-up.

Discussion
Periocular pilomatrixoma is indeed an infrequent clinical condition in ophthalmic clinics [10]. To the best of our knowledge, the present study analyzed the largest case series of periocular pilomatrixoma in English literatures in recent years.
Pilomatrixoma were mostly found in female patients in the rst 2 decades of their lives [1]. Our ndings here were in accordance with the conclusions before (female: 56 %,younger than 20 years: 56 %). The periocular lesions mostly develop at upper eyelids and eyebrows, without left or right predominant. We also found all tumors located at upper eyelids or eyebrows and both right and left sides were equally affected (right vs. left: 52 % vs. 48 %) [7][8][9].
In general, the gross appearance of pilomatrixoma is a kind of rm, well-circumscribed nodule with or without epidermal ulceration. Although the size of tumors varied from each other, most of the periocular pilomatrixomas were smaller than 1 cm [11]. Upon CT scan, the lesions are always well-circumscribed and isodense relative to adjacent skeletal muscle with different degrees of calci cation [12].
The tumors were composed of two kinds of typical tumors: basophilic cells at peripheral site and shadow cells at central site. Other pathologic features including calci cation and foreign body giant cells [13]. The incidence of calci cation ranges from 69 % to 85 % as reported before and the foreign body giant cells are always located around the calci ed epithelial cell mass [3,10]. We observed 23 cases (92 %) had calci cation and 18 cases (78 %) had foreign body giant cells in their excised biopsies.
Recently, multiple pilomatricomas were noted, which are mostly related to systemic diseases like Gardner syndrome (GS), Turner syndrome (TS), etc [14]. However, to the best of our knowledge, no multiple pilomatricomas has been reported to derive from ocular adnexae till now. In our analyzed cases, no multiple pilomatricomas was found, either.

Conclusion
In summary, we analyzed 25 Chinese patients diagnosed as periocular pilomatricoma from one ophthalmic clinic in the past decade. It was con rmed that the demographic and clinical characteristics of this disease were consistent with the current knowledge. Declarations