Spinal epidermoid cyst
Spinal epidermoid cysts are cystic tumours lined by squamous epithelium. Unlike dermoid cysts, they do not contain skin appendages (hair follicles, sweat glands, sebaceous glands) 10.
They are usually extramedullary but rarely can be intramedullary 1. They may be congenital or acquired.
This article specifically relates to spinal epidermoid cysts. For a discussion of intracranial epidermoid cysts refer to the article: intracranial epidermoid cyst.
Spinal epidermoid cysts are uncommon. They comprise between 0.5% and 1% of all spinal tumours but account for up to 10% of intraspinal tumours in children 2.
Unlike intracranial epidermoid cysts, which are almost always congenital in origin, most spinal epidermoid cysts are acquired. Although present since birth, congenital epidermoid tumours often do not present until the second to fourth decade of life 5. Males are more commonly affected than females.
Epidermoid cysts are commonly associated with spinal malformations such as spina bifida and hemivertebrae 8,9.
Spinal epidermoid cysts may be asymptomatic and discovered incidentally. If symptomatic, motor disturbances, pain, sensory disturbances, and bowel or bladder dysfunction may be present 3.
Epidermoid cysts are benign. Histologically, they consist of stratified squamous epithelium supported by an outer layer of collagenous tissue. Progressive desquamation and breakdown of keratin from the epithelial lining into the interior of the cyst produce the characteristic content 8.
Congenital spinal epidermoids result from anomalous implantation of ectodermal cells during closure of the neural tube between the third and fifth week of embryonic life 1.
Acquired spinal epidermoids are a late complication of lumbar puncture, resulting from implanted epidermal elements into the spinal canal. The time interval between lumbar puncture and tumour diagnosis ranges from 1 to more than 20 years 2. Acquired spinal epidermoids are generally extramedullary and situated near a vertebral interspace 5. Prior to the introduction of styletted lumbar puncture needs, up to 40% of spinal epidermoid cysts were attributed to lumbar puncture. The incidence of this phenomenon has decreased significantly over the recent decades, but sporadic case reports still exist 7.
Congenital epidermoids usually occur at the conus or cauda equina. Acquired cysts are found in the lower lumbar region 2.
In advanced cases, there may be scalloping of the vertebral bodies or a scoliosis 5.
- well circumscribed mass
- hypodense (similar to CSF)
- minimal to no enhancement
- calcification is rare
- potential osseous changes include an expanded spinal canal, laminar thinning and vertebral body scalloping 5
- well-defined lesion
- generally no perilesional oedema 6
Although variable, typical signal characteristics include:
- T1: hypointense (similar to CSF)
- T2: hyperintense (similar to CSF)
- FLAIR: hyperintense compared to CSF
- T1 C+ (Gd): no enhancement or a thin rim of capsular enhancement
- DWI: bright (with corresponding low intensity on ADC map)
Signal intensity may be homogeneous or heterogeneous according to the variable water, lipid and protein composition of the cyst 6.
Treatment and prognosis
Spinal epidermoid cysts are slow growing. Surgery is the treatment of choice. Complete excision is usually possible and is curative 5. If the cyst wall is tightly adherent to the cord parenchyma, the wall should be left in place, however this leads to a risk of recurrence 6.
General imaging differential considerations include:
spinal arachnoid cyst
- no restriction on DWI
- signal suppression on FLAIR
- vertebral anomalies uncommon
spinal dermoid cyst
- usually contains fatty elements
- less likely to demonstrate diffusion restriction on DWI
- patients are usually younger than 20 years of age
spinal neurenteric cyst
- thoracic and cervical regions most common
- usually ventral to spinal cord
- associated vertebral anomalies common
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- 9. Kikuchi K, Miki H, Nakagawa A. The utility of diffusion-weighted imaging with navigator-echo technique for the diagnosis of spinal epidermoid cysts. AJNR Am J Neuroradiol. 21 (6): 1164-6. AJNR Am J Neuroradiol (citation) - Pubmed citation
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