Postauricular dermoid cyst: a rare lesion in an extremely rare location

Dermoid cysts are benign lesions commonly seen in the body’s midline, such as the orbit, oral cavity, and nose. They are rare in the head and neck and exceptionally rare in and around the auricle. A case of postauricular dermoid cyst in a 28-year-old female patient is reported. The clinical features, diagnosis, and management of this rare clinical condition are reviewed. A postauricular dermoid cyst is an extremely rare clinical condition; however, it should be considered in the differential diagnosis of any cystic lesion around the auricle.


Background
A cyst is defined as a closed abnormal sac with a distinct wall that may contain a liquid, semi-liquid, or gaseous material, and it is differentiated from an abscess by the absence of pus accumulation [1].
Dermoid cyst is an uncommon benign lesion in the head and neck region [2]. Head and neck dermoid cysts constitute about 7% of all dermoid cases [3]. Dermoid cysts are described as soft, cystic, unilocular, and moveable lumps [4]. They commonly have no symptoms unless they get infected [4]. The presence of skin adnexal features such as hair follicles and sebaceous glands, as well as the squamous epithelium, characterizes the dermoid cysts [5]. Dermoid cysts are rare in the head and neck, and they are extremely rare in the post-auricular region with only very few cases reported in the literature [5]. The treatment of choice for a dermoid cyst is complete surgical excision to prevent a recurrence. The prognosis is excellent without further complications.

Case presentation
A 28-year-old female patient with no previous medical illnesses presented to the otorhinolaryngology clinic with a right postauricular swelling for about 2 years. She had no symptoms of pain, fever, discharge, or hearing impairment; no history of recent ear infection; and no history of postauricular trauma or surgery. The patient denied weight loss or night sweating. Personal and family history were unremarkable.
On examination, the patient was well-looking with normal vital signs. Right ear examination revealed a 2 × 2 cm well-defined, soft, cystic, non-tender swelling in the postauricular region with no signs of acute inflammation. There was no sinus, fistula, scar, or other skin abnormalities. The right auricle, external auditory canal, and tympanic membrane were normal. Examination of the throat, nose, left ear, and neck was unremarkable.
Complete blood count, ESR, renal function test, and serum electrolytes all were within normal limits. Fine needle aspiration cytology result of the right postauricular cyst aspirate was nonconclusive. For diagnostic and therapeutic indications, the patient underwent complete surgical excision of the right postauricular cyst under local anesthesia (Figs. 1 and 2). Gross examination of the excised specimen showed a tuft of hair inside the cyst cavity (Fig. 3). Histopathological

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The Egyptian Journal of Otolaryngology The patient had a smooth postoperative recovery, and there was no evidence of recurrence after a followup period of 15 months (Fig. 6).

Discussion
In general, cystic malformations are classified into epidermoid, dermoid, and teratoid cysts. These are lined with stratified squamous epithelium which is derived from the ectodermal component of the germ layer. Dermoid cyst is characterized by the presence of skin adnexal structures such as hair follicles and sebaceous glands along with the squamous epithelium. In contrast, the epidermoid cyst only has a simple squamous epithelium with no adnexal structures while the teratoid cyst is characterized by the presence of other abnormal tissues derived from all three germinal layers such as muscles, bone, and cartilage [6].   The exact histopathological mechanism of dermoid cyst formation remains mostly unknown; however, the following theories have been postulated regarding the origin of dermoid cysts: (i) there is congenital inclusion of dermal and epidermal elements of germ layers in deeper tissues along the embryonic lines of fusion, (ii) implantation of dermal and epidermal elements of surface epithelium which may proliferate and keratinize can occur after birth due to trauma, and (iii) growth can occur from the rest of the totipotent stem cells displaced from the blastomere [7].
Head and neck dermoid cysts are considered rare. About 7% of all dermoid cyst cases occur in this region, and they are mostly found in the lateral eyebrow followed by the submental region and the floor of the mouth [8]. It is extremely rare to involve the auricle or the postauricular region. In one study done by New and Erich, they did not report any single case of postauricular dermoid cyst in their analysis of 1495 patients [9]. Table 1 summarizes some of the most recently reported cases of postauricular dermoid cysts. It clearly shows that the most common presenting symptom is a painless lump behind the ear. It also demonstrates that this rare clinical entity affects both males and females in any age group. After an extensive search in the literature and to the best of our knowledge, this case is the first case of postauricular dermoid cyst reported from the Kingdom of Saudi Arabia.
Although the most common presentation of the postauricular dermoid cyst as seen in our case is painless swelling, it may get inflamed and become painful [10,11].
Postauricular dermoid cyst usually takes a longer period of time to be noticed by the patients due to its location which makes it unnoticeable by the patients and because of its painless character. Most of the patients seek medical care for cosmetic purposes [12].
Fine needle aspiration cytology is helpful to differentiate the dermoid cyst from other lesions such as sebaceous cyst, lymphadenopathy, lipoma, and hemangioma [13]. Diagnosis of the dermoid cyst is usually established by the characteristic histopathological features including the stratified squamous epithelium and the adnexal structures.
Intracranial extension is common with midline or scalp lesions, and due to this potential, the radiological imaging should be done before any biopsy or intervention [14]. Surgical excision is the recommended treatment of choice for dermoid cysts in any location [15]. Early surgical intervention is preferred to establish the diagnosis and to have a better cosmetic outcome [16,17].
Complete surgical excision with removal of all cyst walls and contents is essential to prevent local recurrence [16]. Infected cyst has a greater risk of recurrence reaching 20% [18].
The overall prognosis for patients with a dermoid cyst is excellent, especially when there is no intracranial or intraspinal extension [16]. Malignant transformation of a dermoid cyst is extremely rare; however, it has been reported in some cases [19,20].

Conclusion
Although dermoid cyst of the postauricular region is an extremely rare condition, it should be considered in the differential diagnosis of postauricular lumps. Complete surgical excision is mandatory to prevent a recurrence.