A six-year-old girl presented to the emergency room with a two-month history of progressive low back pain radiating to the buttocks and legs, resulting in difficulty walking. The pain was worse when she lay down and had started interfering with her sleep. On examination, she had no neurological deficits, and the straight leg raising test was negative. There was no tenderness or deformity of the spine. There was no prior history of spinal procedures, including lumbar puncture, in this patient.

On MRI (Figure 1), a centrally located 1.2 × 1.3 × 1.4 cm non-enhancing extramedullary mass was noted at the level of L2/L3. The mass was splaying and distorting the surrounding cauda equina nerve roots. Furthermore, the lesion demonstrated uniform restricted diffusion. The lower spinal cord was normal in morphology, and the conus medullaris terminated at the level of the superior endplate of L1.

Figure 1. Preoperative MRI of the patient: sagittal (A) T1-weighted, (B) post contrast-T1-weighted, (C) T2-weighted, and (D) axial T2-weighted. MRI depicted a non-enhancing intradural extramedullary mass.

Urgent surgical excision of the lesion was recommended after an overnight rise in her post-void residual urine, due to concern for cauda equina syndrome. An L2–L3 laminoplasty was performed, and a globular, gray tumor was encountered on opening the dura. Upon cutting the tumor capsule, we observed pearly white flaky material and hairs (Figure 2A). The tumor was not attached to any of the nerve roots and was completely excised.

Figure 2. Intraoperative images (A) immediately upon opening the capsule and (B) during internal debulking of the dermoid cyst. The 4-month postoperative MRI demonstrated complete resection of the intraspinal mass on (C) T2-weighted and (D) T1-weighted images.

Histopathological examination of the resected tumor revealed a cyst lined with keratinizing stratified squamous epithelium and skin adnexal structures. Hair follicles, sebaceous glands and a chronic inflammatory infiltrate beneath the epithelium were also observed. Squames and vellus hairs were observed within the cyst. All findings were consistent with a diagnosis of a dermoid cyst.

Postoperatively, the patient’s pain and discomfort significantly improved, and her gait normalized. At four months follow-up, the patient had regained normal function and was able to run and play. Postoperative MRI (Figure 2B) confirmed complete resection of the tumor.

Spinal dermoid cysts are very rare, representing ∼ 1% of spinal tumors. ^{Reference Sarkar and Rajshekhar1} The majority of spinal dermoid cysts are associated with spinal dysraphism, ^{Reference Prasad, Sinha and Krishna2 , Reference Cheng, Li and Gao3}  including lipoma, thickened filum terminale and dermal sinus. In children, up to 60% of dermoid cysts are associated with a dermal sinus. ^{Reference Sarkar and Rajshekhar1} In our patient, there was no clinical or radiological evidence of a dermal sinus or spinal dysraphism, making it more unusual.

Diffusion-weighted MRI showing restricted diffusion, ^{Reference Kukreja, Manzano, Ragheb and Medina4} and mild T1 hyperintensity that represents adipose tissue is a clue to diagnosing dermoid cysts. Intraoperatively, dermoid cysts are typically not adherent to nerve roots and contain dermal elements such as sebaceous glands and hair follicles, unlike schwannomas, neurofibromas and epidermoid cysts. ^{Reference Beechar, Zinn and Heck5}

The purpose of this report is to highlight that dermoid cysts must be in the differential diagnosis of lumbar intradural tumors in children, even when there are no signs of a low-lying spinal cord or other features of spinal dysraphism.