1 Introduction

Spinal epidermoid cysts are rare, benign, slow-growing lesions commonly located in the lumbosacral region, which are intradural and extramedullary.¹ The relatively rare thoracic spine epidermoid cysts are commonly intradural intramedullary, with a reported incidence of 0.8 %.² They are congenital or acquired lesions, the latter usually associated with trauma or invasive spinal procedures.³

2 Case report

A 59-year-old female presented with progressive gait instability and bilateral lower limb weakness for two months duration. She had no history of trauma or previous spinal procedures. On neurological examination, she had motor power of 3/5 in both lower limbs as per the MRC scale. Knee reflex and plantar reflex were exaggerated and bilateral plantar was found to be extensor with intact sensation in all dermatomes with no bladder or bowel dysfunction.

2.1

2.1 Diagnostic assessment

MRI of the whole spine revealed a well-defined T1 hypo to isointense and T2 hyperintense intradural extramedullary lesion (IDEM) at T9-T10 level measuring about 15x9x8mm in dimensions. Postcontrast T1weighted MRI showed some enhancement in the centre of the lesion suggestive of benign epidermoid cyst (Fig. 1).

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Fig. 1 Preoperative MRI images showing (A, E) T2W sagittal and axial images showing hyperintense lesion (B, D) STIR sagittal and axial images showing hyperintense lesion (C) T1 Precontrast T1W sagittal image showing hypointense lesion with some iso intensity in the centre (E, F) Post-contrast T1W sagittal and axial images showing few enhancement in the centre of the lesion.

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2.2

2.2 Therapeutic intervention

In view of progressive neurological deficit and gait instability, she was planned for surgical excision and biopsy. Subsequently, the patient underwent T9 and T10 complete laminectomy followed by microsurgical excision of the intradural extramedullary lesion under neuromonitoring guidance. A well-encapsulated yellowish tumour was removed en bloc and margins were cleared of tumour remnants. Histopathological examination revealed a benign epidermoid cyst which was lined by stratified squamous epithelium with intraluminal lamellated keratin (Fig. 2). There were no dermal appendages or any evidence of malignancy noted.

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Fig. 2 (A, B, C): Histopathological examination with typical cyst wall lined by stratified squamous epithelium with intraluminal lamellated keratin, no dermal appendages or evidence of malignancy.

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In the immediate postoperative period, the patient was gradually mobilised with walker support. The patient's neurology improved over a period of time and at six months of follow-up, there was complete neurological recovery with improved gait pattern. At one year follow-up MRI showed no evidence of recurrence or residual lesion (Fig. 3).

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Fig. 3 Postoperative MRI images (A, D) T2 W sagittal and axial, B) T1 W sagittal, C) STIR sagittal at one year showing no evidence of recurrence.

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3 Discussion

Spinal epidermoid cysts are benign, slow-growing lesions with an overall <1 % incidence with bimodal age distribution and slightly female preponderance.^4,5 They are classified into three types based on the aetiology. The most commonly acquired ones are commonly associated with trauma, surgical or invasive spinal procedures such as lumbar puncture, causing the inclusion of cutaneous epithelial tissue within the intraspinal compartment.^3,4,6,7

Congenital cysts are usually associated with the entrapment of ectodermal cells into the spinal canal during the early weeks of gestation between 3rd & 5th weeks, in cases of defective neural tube closure like spina bifida, syringomyelia or associated cutaneous anomalies like the presence of dermal sinus or the tuft of hair.^4,8,9

Another less common variant is isolated ones with no history or features of spinal dysraphism, repeated lumbar puncture, spinal trauma or surgery.¹⁰ Most of these cysts occur at the lumbosacral region with the intradural extramedullary location.¹ Epidermoid cysts occurring in the thoracic spine are relatively rare and are commonly intradural intramedullary lesions.² There are very few cases of isolated thoracic epidermoid cysts in the intradural extramedullary location reported in the literature (Table 1). Our case is an isolated variant reported in an elderly female without any acquired causes.

Symptoms of epidermoid cysts usually vary with the level of the lesion, with the most common presenting features of thoracic spine involvement being axial back pain with weakness or numbness of lower limbs with difficulty in walking.⁵ They present with long-standing symptoms due to the slow-growing nature of these cysts. Acute presentation with rapid neurological deterioration has been reported rarely. Probable causes for rapid deterioration were trauma, sudden increase in size and rupture of the cyst wall with surrounding inflammation.^4,8,11

It might be challenging to distinguish between an “isolated” spinal epidermoid cyst and other conditions. The MRI characteristics of these lesions may resemble those of an arachnoid cyst on T1-and T2-weighted sequences and post-contrast images may lack conclusiveness. Furthermore, spinal epidermoid cysts must be distinguished from spinal dermoid cysts and spinal neurenteric cysts prior to surgery. As with intracranial epidermoid cysts, differential diagnosis can be supported by Diffusion Weighted Imaging (DWI), Fluid Attenuated Inversion Recovery (FLAIR) MRI sequences, and, in certain instances, CT scans.^4,12–14 Characteristics of these lesions in MRI sequences are depicted in the table (Table 2).

They are commonly referred to as pearly tumours as they look like white encapsulated mass intraoperatively. Histologically, epidermoid cysts are lined by stratified squamous epithelium with an outer layer of collagenous tissue. Progressive desquamation of keratin into the cyst wall produces soft white-like material rich in cholesterol crystals.^15–17

The surgical management for spinal epidermoid cysts is total resection of the cyst along with its entire content while maintaining the subarachnoid microanatomy.¹⁸ In cases where total resection is not possible, cyst decompression followed by piecemeal removal should be advised.⁷ Care must be taken to avoid spillage of cyst contents into subarachnoid space to prevent late chemical subarachnoiditis.¹⁹ Microanatomy of the subarachnoid compartment was studied by Barbagallo et al. who divided the subarachnoid space into anterior and posterior spaces by dentate ligament.¹⁸ The anterior subarachnoid space is a single compartment with no septa, while the posterior subarachnoid space is divided into four compartments: midline dorsal septa and two posterolateral septa. Clear preoperative evaluation of the location of the cyst in these compartments should be established for safe and complete tumour excision and to prevent iatrogenic traction injury on dorsal nerve rootlets and recurrence.

4 Conclusion

A spinal epidermoid cyst should be considered a possibility in a patient with no previous surgical history and rapid neurological deterioration. Proper radiological evaluation using special sequences to diagnose the epidermoid cyst and a complete understanding of subarachnoid microanatomy are essential for complete cyst excision and good clinical outcomes.

CRediT authorship contribution statement

Niventhiran Kuppusamy: Conceptualization, Methodology, Writing – original draft. Karthik Ramachandran: Supervision, Validation, Writing – original draft. Gnanaprakash Gurusamy: Data curation, Investigation. Ajoy Prasad Shetty: Writing – review & editing. Shanmuganathan Rajasekaran: Writing – review & editing.

Informed consent

Written informed consent was obtained from this patient to publish this case report.

Ethical statement

IRB approval is not required for this case report. Informed consent has been obtained from the patient for the publication of case details.

Financial support and sponsorship

The authors declare that no financial support or funding was received.