Dermatology Online Journal

Two cases of steatocystoma simplex in infants
Mari Sunohara MD, Toshiyuki Ozawa MD, Kuniyuki Morimoto MD, Chiharu Tateishi MD, Masamitsu Ishii
Dermatology Online Journal 18 (7): 2

Osaka City University Graduate School of Medicine, Osaka, Japan

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Abstract

Steatocystoma simplex is a rare benign cutaneous cyst that is thought to be a circumscribed malformation arising from the pilosebaceous duct junction. Reports describing steatocystoma simplex are scarce and many issues remain to be clarified, including frequency and age distribution. Steatocystoma simplex is generally considered to be a solitary, non-inherited tumor arising in adults; there have been no previous reports of steatocystoma simplex in infants. We encountered two cases of steatocystoma simplex arising on the head in infants less than 2 years old. Herein we discuss the clinical and pathological characteristics of these cases.

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Introduction

Steatocystoma simplex is often compared with steatocystoma multiplex, which shares similar pathological features. Steatocystoma simplex differs from steatocystoma multiplex in being a solitary cystic nodule with no family history that is comparatively rare. Steatocystoma multiplex is an autosomal dominant condition that presents with multiple lesions, but is otherwise identical in appearance and histology to steatocystoma simplex [2].

There have only been a few reports since 1982, when Brownstein reported 30 cases of steatocystoma simplex as a solitary non-heritable counterpart of steatocystoma multiplex [5]. Our extensive search of the English literature revealed only nine case reports concerning steatocystoma simplex up to 2010, excluding those reported by Brownstein. Therefore, many aspects of steatocystoma simplex remain unknown, including its differences from steatocystoma multiplex, true incidence, and peak age of onset. Steatocystoma simplex was believed to be a solitary tumor arising in adults because as it had never been observed in children aged 15 years or younger [3]. However, we report two cases of steatocystoma simplex in children less than 2 years of age.

Case reports

Case 1. A 2-year-old girl presented with a mobile, compressible subcutaneous mass located near the lateral border of her outer left eyebrow. Her parents had noticed the lesion when she was 1 year and 3 months old and it had been under observation since then. The lesion had gradually increased in size over the past year. At the initial visit, it was 1 cm in diameter. The patient’s nails, teeth, and hair were normal and there was no family history of similar lesions.

Laboratory tests revealed no abnormal findings. Ultrasonography revealed a well-defined cyst with a low internal echo. CT revealed that the mass was a cyst in contact with the periosteum, which had a slightly high-density wall and a homogeneous low-density interior. A dermoid cyst was suspected, so surgical removal was performed followed by histopathological examination.

Figure 1	Figure 2
Figure 1. A subcutaneous mass is observed at the lateral aspect of the left eyebrow Figure 2. Head CT reveals low density lesion

Intraoperative examination confirmed no invasion of the overlying skin or the periosteum and the lesion was soft and mobile. Histopathological examination revealed the presence of squamous epithelium lining the cyst wall and scattered sebaceous glands were observed. Therefore, steatocystoma simplex was diagnosed (Figures 1 and 2). However, a cyst wall with a crenulated eosinophilic lining was not observed.

Case 2. A 4-month-old girl was brought to our department with the chief complaint of a mass located at the glabella. At the initial examination, a subcutaneous mass approximately 1 cm in diameter was identified, which was compressible and mobile relative to the surrounding tissues. There were no abnormalities of the overlying skin. No other abnormal findings were noted and no family member had presented with a similar lesion. Laboratory tests revealed no abnormalities. Plain X-ray films also revealed no abnormalities. Ultrasonography displayed a cystic mass with a well-defined border and low interior echo. MRI revealed an encapsulated subcutaneous mass with high-intensity contents on T1-weighted images and with high-intensity contents on T2-weighted images obtained with fat suppression.

Figure 3a	Figure 3b
Figure 3a. The cyst has partially ruptured. The presence of squamous epithelium in the cyst wall is confirmed. (Low-power view) Figure 3b. Attachment of sebaceous glands to the cyst wall can be observed. (High-power view)

The mass was removed surgically. Intraoperative examination confirmed a soft mass with no invasion of the surrounding tissues. Pathological examinations indicated that the cyst wall was formed by stratified squamous epithelium without a crenulated eosinophilic lining and sebaceous glands were attached. Accordingly, steatocystoma simplex was diagnosed (Figures 3a and 3b).

Discussion

We encountered two rare cases of steatocystoma simplex in infants.

Brownstein first reported this condition and described its clinical and histological features in 30 patients (16 women and 14 men) [5].

Figure 4
Figure 4. A mass is located beneath the skin at the glabella

Their ages ranged from 15 to 70 years (median: 39 years) and there was no family history of similar disorders. He also reported that the clinical features were like those of individual steatocystoma multiplex lesions [5].

Since then (up to 2010), our extensive search of the literature revealed only 9 cases of steatocystoma simplex, which were almost divided evenly between men and women ranging in age from 17 to 69 years. There have been no reports of steatocystoma simplex in young children so far [1, 2, 6, 7-12].

Figure 5a	Figure 5b
Figures 5a, 5b, and 5c. A high intensity is observed on both T1- and T2-weighted images obtained with fat suppression.

Figure 5c

We also examined the age of onset reported for steatocystoma multiplex thus far because steatocystoma multiplex shares similar pathological findings with steatocystoma simplex, and found that the age at the time of surgery (biopsy) ranged from 5 to 81 years, with a mean of 37 years. No reports about steatocystoma multiplex in infants were found. This suggests that, even including steatocystoma multiplex, the onset of these lesions in young children is rare.

At present, steatocystoma simplex is considered to be an adult disease [3] and it is generally believed that both steatocystoma simplex and steatocystoma multiplex develop after adolescence. However, the pathogenesis of steatocystoma simplex and steatocystoma multiplex remains to be elucidated. The cases presented in this report suggest the possibility that steatocystoma simplex may also arise congenitally. Therefore, it can be considered as a childhood cystic disease that requires differential diagnosis (Table 1).

With regard to cystic diseases in children, dermoid cyst and epidermoid cyst occur at a high frequency. In addition, discrimination from vellus hair cyst is important.

Figure 6a	Figure 6b
Figures 6a and 6b. (a) Low-power view, (b) High-power view. A cyst lined by stratified squamous epithelium is observed with sebaceous glands attached to the wall.

Currently, it is difficult to distinguish steatocystoma from other cystic lesions based on clinical features alone, so imaging and histological findings are critical for discrimination [2, 8].

Based on the fact that steatocystoma contains solid, yellow lipid in the interior [3], a high signal intensity will be obtained on T1- and T2-weighted images with fat suppression, reflecting the internal solid fatty components as described in Case 2. According to our pathological findings, the cyst is lined by a thin layer of stratified, squamous epithelium and there is no granular layer with a characteristic dense hyaline layer present on the epithelium. The luminal surface is undulating and the pathognomonic feature is the attachment of sebaceous glands to the cyst wall [2, 3, 12].

Differences from vellus hair cyst in terms of imaging findings are still unclear and their clinical features also share many similarities; discrimination is often challenging. On pathological findings, the wall of a hair cyst is lined with stratified squamous epithelium and the lumen contains small hairs and keratin17 [1]. Tomkova et al reported that steatocystomas express keratins 10 and 17 in contrast to eruptive vellus hair cysts, which express only keratin 17 [13].

In the case of dermoid cyst, MRI is considered useful for discrimination because it shows the same high signal intensity as the surrounding soft tissues on T2-weighed images. On pathological examination, a dermoid cyst has thicker walls, lacks the thick hyaline luminal border, and has prominent pilosebaceous contents with the occasional presence of other adnexal elements [1, 2, 3].

Epidermal cyst is the most frequent subcutaneous tumor, but it rarely occurs in young children. Pathologically, the cyst is surrounded by several layers of squamous epithelial cells and the lumen is filled with loosely packed lamellae of degenerated keratin, known as a keratin pearl. Imaging is also considered useful for distinguishing among these cysts. It has been reported that steatocystoma simplex has solid lipid contents, with a high intensity likely to be observed on both T1- and T2-weighted images [9], whereas an epidermal cyst will show a low intensity on T1-weighted images and a high intensity on T2-weighted images [14]. Thus, MRI can be helpful for distinguishing between these two conditions.

Because there have only been a few reports about steatocystoma simplex, many points regarding its pathogenesis are still unknown and it has been considered to be an adult disorder. However, we encountered two cases of steatocystoma simplex in infants. These cases suggest the possibility that steatocystoma simplex, which has thus far been regarded as an adult disorder, may also arise congenitally. Therefore, if a subcutaneous mass is observed in an infant, steatocystoma simplex should be considered in the differential diagnosis.

In the future, we plan to accumulate more cases of steatocystoma simplex and investigate its genetics, incidence, and background in order to assess its actual occurrence as well as its association with steatocystoma multiplex.

References

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