A 15-year-old female presented with a submental swelling, located beneath the chin, which had been present for approximately two months. Her past medical and surgical histories were unremarkable, with no history of chronic medication use or known drug allergies. There was no significant family history. She denied cough or any recent flu-like illness.

Laboratory investigations demonstrated normal renal function, with a blood urea level of 19.7 mg/dL and serum creatinine of 0.52 mg/dL. Random blood glucose was within the normal range at 85.8 mg/dL.

Complete blood count revealed microcytic hypochromic anaemia, with haemoglobin of 9.7 g/dL, haematocrit of 31.5%, MCV of 66.7 fL, MCH of 20.5 pg, and MCHC of 30.8 g/dL. Platelet count was mildly elevated at 437 × 10⁹/L. The total white blood cell count was within normal limits at 6.1 × 10⁹/L.

ESR was mildly elevated at 23 mm/hr. Thyroid function tests were within normal limits, with TSH of 2.0 μIU/mL and free T4 of 15.6 pmol/L.

Ultrasound demonstrated a large complex cystic mass in the submental region, extending inferiorly and deeply into the sublingual space, measuring approximately 53 × 40 × 37 mm. The lesion was hypovascular and caused compression of the surrounding tissues, with no sonographic features of invasion. The findings were suggestive of a dermoid cyst.

Both thyroid lobes were normal in size and demonstrated homogeneous echotexture and normal vascularity, with no focal lesions. No significant pathological cervical lymphadenopathy was identified. The bilateral submandibular and parotid glands were normal, with no focal lesions.

Through a transverse submental incision, dissection was carried out beneath the submental musculature to identify and excise the dermoid cyst. The cyst was intentionally ruptured during dissection. The operative field was thoroughly irrigated with normal saline, and meticulous haemostasis was achieved. A corrugated drain was placed, and the wound was closed in layers.

Histopathological examination of the submental cystic specimen demonstrated an inflamed dermoid cyst. The cyst was lined by stratified squamous epithelium and contained abundant lamellated keratin, with associated skin appendages including hair follicles and sebaceous glands.

Focal ulceration and loss of the epithelial lining were associated with a prominent mixed inflammatory infiltrate comprising histiocytes, lymphocytes, plasma cells, and neutrophils, accompanied by vascular congestion and fibrosis. Skeletal muscle fibres were also identified within the specimen.No evidence of malignancy was identified.

The patient had an uncomplicated postoperative recovery following excision of the submental dermoid cyst. The wound remained clean and well approximated, with the corrugated drain removed appropriately. The patient was discharged in stable condition with routine postoperative follow-up arranged.