Sublingual dermoid cyst tracking down to the anterior neck in a child: A case report

An 11-year-old child was brought to our hospital due to swelling in the anterior neck. The patient reported no symptoms other than the neck swelling. There was no history of trauma or surgery.

The ultrasound examination of the anterior neck revealed a clearly defined cystic lesion with internal small echogenic round floating contents giving sack of marble appearance. These floating contents represent fat globules. No signs of vascularity were detected in the colour Doppler study (Figure 1). A similar cystic lesion was also observed in the sublingual region (Figure 2).

On an axial non-contrast CT scan, a well-defined cystic lesion with a thin wall was identified in the left paramidline area of the neck. The lesion exhibited areas of internal fat attenuation (-20HU). It was causing compression on the left side of platysma muscle, but there was no evidence of invasion. The left lobe of the thyroid gland appeared separate from the lesion. Additionally, a smaller, similar lesion was detected in the sublingual region above the larger lesion. Both lesions exhibited peripheral enhancement in contrast-enhanced images (Figures 3, 4 and 5). Furthermore, an axial contrast-enhanced image revealed a thin, peripherally enhancing tract that extended from the sublingual space posteriorly towards the lateral aspect of the neck (Figure 6).

Background

A benign cutaneous developmental abnormality called a dermoid cyst develops when ectodermal components are trapped along the lines of embryonic closure [1]. Dermoid cysts are most common in the testes and ovaries, but can occur at any embryologic fusion point in the body. Dermoid cysts on the floor of the mouth are believed to be caused by the sequestration of ectodermal tissue in the midline during the fusion of the first (mandibular) and second (hyoid) brachial arches [2]. These benign tumours have stratified squamous epithelium lining them, mature skin appendages on their wall, and keratin and hair-filled lumens. Although dermoid cysts are thought to be congenital, not all of them are identified at birth [3,4,5]. Approximately 40% of dermoid lesions are diagnosed at birth, while 60% are diagnosed by the age of five [3].

Clinical perspective

Dermoid cysts can be found anywhere on the body. In the head and neck, they are most often found in the frontal, occipital, and supraorbital areas. Oral cavity dermoids accounted for approximately a quarter of the head and neck dermoids and 1.6% of the total number. The most common location within the oral cavity is the anterior portion of the floor of the mouth [6]. Like in our case, dermoid cysts typically develop as solitary lesions that are asymptomatic, non-pulsatile, and non-compressible [7].

Clinical examinations can be used to evaluate oral cavity dermoid; however, imaging is typically required for a more thorough evaluation. For an appropriate diagnosis and treatment, it may be necessary to utilize computed tomography, magnetic resonance imaging, or ultrasound to precisely diagnose the extension of the lesion to deeper structures [8].

Imaging perspective

Ultrasound can identify intra-cystic floating corpuscles, or the "sack of marbles sign", which are pathognomonic for a dermoid cyst. Dermoid cysts are typically hypodense on CT scans, hyperintense on T1-weighted MRI scans, and intermediate to hyperintense on T2-weighted MRI scans due to their lipid contents. These lesions show suppression in fat-suppressed sequences in MRI, like STIR and T1FS [9]. In our case, the communication might be due to the slow trickling of the contents of the lingual dermoid into the anterior neck during upright positions.

Outcome

The treatment of sublingual cyst is surgery. Once the cyst is removed, it is very rare for it to recur [10]. The choice of surgical approach depends on the location of the cyst in relation to the mylohyoid muscle. If the cyst is large or located beneath the mylohyoid muscle, it is often removed through an external incision. However, if the cyst is small or located above the mylohyoid muscle, an intraoral approach is used. To plan surgery, it is important to identify the exact location of the cyst to the mylohyoid muscle using CT or MRI imaging [10,11].