Frontotemporal dermoid cyst with incomplete dermal sinus tract in an adult: A case report

INTRODUCTION

Dermoid cyst is typically a congenital benign tumor considered to be derived from abnormal ectodermal fusion[9] during fetal development. It accounts for 0.04–0.7% of all intracranial tumors.[4,12,20] Intracranial dermoid cyst tends to occur in the midline[9] whereas scalp (extracranial) dermoid cyst may occur off-midline.[18] However, in the past literature, we have several rare reports on these intracranial non-midline dermoid cysts associated with dermal sinus tract, especially in children.[2-4,6] We recently experienced a similar case who was diagnosed in adult. This case reminds us that non-midline dermoid cyst with continuous sinus tract may go undiagnosed until adulthood. This type of dermoid cyst sinus tract complex has not been reported, to the best of our knowledge. We reviewed the past literature similar to our case to shed light on the frontotemporal dermoid cyst sinus tract complex with emphases on its characteristics and management strategy.

CASE REPORT

History and examination

A 43-year-old female presented with recurrent subcutaneous mass in the left superolateral orbital region [Figure 1a]. The mass has been present since she was 4 years old, and there have been no episodes of local infections. She had a history of partial resection of this mass at another department 2 years ago, where only subcutaneous component of the cyst was ligated and resected. Pathological diagnosis was dermoid cyst. In 2 years’ follow-up, she developed a recurrent mass in the same region. Due to her active asthma and the history of adverse events that occurred after contrast MR imaging, contrast imaging studies were not performed. CT and MR imaging showed a subcutaneous mass with possible continuity to the Sylvian cistern by a tract in the sphenoid ridge and lesser wing of the sphenoid bone [Figure 1b and c]. As 2 years have passed since the initial surgery, we speculated the lesion had already penetrated the subarachnoid space through the dura based on the preoperative imaging. While she had no headache or showed any signs of neurological deficits, we decided to reset the mass and the tract to prevent further recurrence.

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Figure 1:: Preoperative images of the recurrent dermoid cyst (a). Note the subcutaneous swelling in the superolateral orbital area (white arrow) Fluid attenuated inversion recovery MR imaging (coronal) showed a well-circumscribed extracranial tumor component of 22 mm in diameter (b). CT (coronal) showed a tract traversing through the sphenoid bone (c).

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Surgical intervention

She underwent frontotemporal craniotomy. When musculocutaneous flap was retracted, the cyst duct was inadvertently damaged, resulting in spill out of greasy and whitish yellow cyst content [Figure 2a]. The tumor was relatively large and fanning toward the skin, suggesting that dissection of the tumor through the temporal muscle and fascia could lead to damage to the frontal branch of the facial nerve.[16] We thus cut the cyst duct and followed the duct toward the bone [Figure 2b] and to the dura. The duct looked ending in a blind pouch at the surface of the dura [Figure 2c] near the lesser wing of the sphenoid bone. As the lumen was exposed, yellowish debris and hair were appreciated. Intradural space was then carefully inspected and showed no evidence of lesion continuity. Finally, the remaining extracranial mass was totally resected with careful inspection of the facial nerve using a nerve stimulator.

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Figure 2:: Intraoperative findings. Part of the tract was inadvertently damaged and greasy and whitish yellow tumor content spilled out (a). The bone around the tumor tract was drilled and the tract was dissected (b), which ended in pouch at the surface of the dura (c).

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Histopathological findings

The resected specimens showed a cystic lesion filled with keratinized debris and a ductal structure which was connected to the cyst. The cyst wall was lined by a stratified squamous epithelium similar to epidermis. It contained adnexa of skin, such as sebaceous glands and sweat glands [Figure 3]. As for the transitional segment from the cystic lesion and the dura, histiocytes infiltration and hyalinized dura were appreciated, with no dermoid components. Consequently, dermoid cyst and sinus tract were diagnosed.

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Figure 3:: A cystic lesion lined by an epidermal-like squamous epithelium contained several sebaceous glands, some of which continuous to the epithelium (a). A ductal structure, traversing through the sphenoid bone, was lined by a thin squamous epithelium with seldom keratinization (b). H&E: Hematoxylin and eosin; Original magnification ×40.

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DISCUSSION

A noteworthy case of subcutaneous dermoid cyst in the left superolateral orbital region accompanied by incomplete dermal sinus tract was described. Even though quite a few case reports have been made despite its rarity,[1-4,8,10-15,17,19-22] our case was unique in that it was diagnosed in adult and that the dermoid cyst was associated with incomplete sinus tract. Nineteen cases of frontotemporal dermoid cysts with sinus tract including ours are summarized in Table. The average age of diagnosis was 6 years. The lesions seemed to be more common in females (five male patients and 14 female patients; P = 0.03 by Chi-squared test) and more common on the right side (right in 13 cases, left in 5, unknown in 1;P = 0.06 by Chi-squared test). The relapses occurred in five patients (26%) due to incomplete excision, but no recurrences were reported after complete excision with the median follow-up period of 8 months (range 1.5 months–8 years). The lesions were extradural in most cases. Dural transgression were reported in only two cases (10%), which was different from the midline lesions in the spine.[7]

Based on these previous reports, we classified the dermoid cyst sinus tract complex into three types (types A, B, and C) [Figure 4]by the location of the sinus tract relative to the dermoid cyst [Table 1]. Type A is characterized by the clinically overt dermal sinus tract ending in pouch with dermoid cyst in the intradiploic, extradural, or intradural areas. This type is diagnosed exclusively in the childhood due to recurrent local infections and discharge from the overt frontotemporal pits. Type B is characterized by the incomplete dermal sinus tract extending outward (toward the skin) from the intradural dermoid cyst. This type may be diagnosed in adults when they become large enough to cause mass effect.[20] Type C is also characterized by the incomplete dermal sinus tract extending inward (away from the skin) from the extracranial dermoid cyst. This type tends to be diagnosed in adults, although more thorough imaging would make it possible to diagnose in children if they presented with subcutaneous swelling. Based on our case (Type C), we believe, this type has a unique embryological mechanism different from the other types A and B, because the vector of the sinus tract is 180° different. It is unlikely that this lesion (Type C) was caused by the previous incomplete surgical resection, as the intracranial component and the sinus tract through the skull had already been present in the MR imaging before the index surgery.

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Figure 4:: Dermoid cyst sinus tract complex is classified into three types based on the positional relationship of cyst and tract. In type A, the complete tract begins from the skin surface and the cyst is along the tract. Please note the relationship of the dermal pits, sinus tract and the cyst to the skin, skull, and the dura. Type B is the intradural dermoid cyst and the incomplete tract extending outward to the skin (arrow). Type C is the dermoid cyst and the incomplete sinus tract extending inward to the dura (arrow). In this type, the facial nerve (FN) branches may be around the cyst mass.

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Table 1:: Past intracranial surgical reports on the frontotemporal dermoid cyst- sinus tract complex. All underwent complete excisions in the end and none recurred thereafter. Most of the cases were diagnosed in children and shared the same positional relationship of the cyst and the tract. The two unique adult cases were put in the lowest two rows for comparison.

CONCLUSION

Dermoid cyst needs to be included in the differential diagnosis of adult-onset subcutaneous mass in the frontotemporal regions. After thorough imaging studies for the presence and extent of the sinus tract, the symptomatic lesion should be excised completely once and for all.