Cause:
- congenital dermal rest / focal expansion of dermal sinus ← inclusion / aberrant implantation of ectodermal cells at time of neural groove closure (3rd–5th week of GA)
- acquired from implantation of viable epidermal / dermal tissue (lumbar puncture by spinal needle without trocar)
Similarities: both composed of
- outer wall formed by collagenous tissue
- inner lining formed by ectodermal tissue only (= stratified squamous epithelium)
Histologic differentiation:
- Epidermoid cyst
- thin squamous lining
- cyst content = waxy white “pearly tumor” composed of desquamated epithelial cells (= keratin, triglycerides, fatty acids, cholesterol crystals)
- Dermoid cyst (may arise earlier in embryonic process)
- thicker lining including calcifications, sebaceous secretions, sweat glands, hair follicles, hair
- forming fat-fluid levels
- cyst content = composed of (1) desquamated epithelium and (2) secretions of sebaceous glands
- nonspecific symptoms: weakness, back pain
- slowly progressive myelopathy ← space-occupying lesion causing irritation / compression of adjacent structures:
- motor + sensory disturbance (paresthesia)
- urinary / fecal incontinence
- acute onset of chemical / aseptic meningitis / arachnoiditis ← spread of cholesterol crystals via CSF ← cyst rupture:
- headache, nausea, vomiting, vertigo, visual problems
- meningism, mental change, hemiplegia, coma
= uni- / multilocular benign cystic tumor lined by stratified squamous epithelium containing skin (dermal) appendages
Path:
- wall ± calcifications (in 31%) and papillary projections along inner surface
- cystic contents of fluid-like mucoid (in virtually 100%) and lipid fatty (67–75%) components
- thick foul-smelling yellow material ← secretion of sebaceous glands + desquamated epithelium
Prevalence: 1–2% of intraspinal tumors; 0.7–1.8% of all CNS tumors
Age at presentation: 2nd–3rd decade; M÷F = 1÷1
May be associated with:
- myelomeningocele, dermal sinus tract (in 20%), hypertrichosis; Currarino triad (= anorectal malformation + sacral dysplasia + presacral mass → severe constipation since birth)
Location: lumbosacral (60%), cauda equina (20%)
Site: extramedullary (60%), intramedullary (40%)
CT:
- almost always complete spinal block on myelography
- CT myelography facilitates detection
- well-demarcated isoattenuating mass ± hypoattenuating fat
- ± wall calcifications + papillary projections
MR:
- uni- / multilocular cystic lesion with variable SI:
- hyperintense on T1WI + hypointense on Gd-enhanced fat-suppressed T1WI (fatty component)
- occasionally hypointense on T1WI + hyperintense on T2WI (fluid secretions from sweat glands within tumor)
- ± fat-fluid level
- NO contrast enhancement (except for small soft-tissue component)
- dissemination of lipid droplets scattered throughout CSF and intra-axially throughout spinal cord
Cx: spontaneous / intraoperative / traumatic dermoid cyst rupture → lipid droplets transported along CSF pathway
Prognosis: high risk of morbidity + mortality (with rupture)
Rx: dependent on symptoms
DDx:
- Epidermoid cyst (without dermal appendages, T1 hypointense + T2 hyperintense)
- Lipoma (homogeneous midline T1-hyperintense lesion with smooth well-defined border)
- Teratoma (heterogeneous enhancement)
- Intraaxial tumor: ependymoma, astrocytoma, hemangioblastoma
= cystic tumor lined by a membrane composed of epidermal elements of skin
Prevalence: 0.2%–1% of intracranial tumors; <1% of spinal cord tumors
Mean age: 34 (range, 3–71) years; M÷F = 1.35÷1.00
May be associated with:
- skin lesion: hairy nevus, dyschromia, angioma, scar
- spinal dysraphism: dermal sinus, spina bifida, hemivertebra, syringomyelia, tethered cord syndrome, dorsal meningocele, diastematomyelia
Mean delay in Dx: 6 years (range, 2 days to 53 years)
Location: upper thoracic (17%), lower thoracic (26%), lumbosacral (22%), cauda equina (35%)
Site: intradural extramedullary (60%), intramedullary (40%)
Growth rate: similar to that of normal skin
- displacement of spinal cord / nerve roots
- NO internal enhancement + faint to NO rim enhancement
Myelography (CT facilitates detection):
- asymmetric filling defect / complete spinal block
DDx: communicating arachnoid cyst typically opacifies
MR:
- circumscribed mass WITHOUT peripheral edema
- variable signal intensity ← differing concentrations of cyst content of keratin + water + cholesterol:
- T1 isointense (especially when tumor small) to slightly hyperintense relative to CSF
- iso- to slightly hyperintense relative to CSF on T2WI
- T1 hyperintense + T2 hypointense “white epidermoid” (rare) ← high protein concentration
- hyperintense to CSF on FLAIR and DWI ← restricted diffusion (DDx: arachnoid cyst (isointense to CSF on FLAIR and DWI)
Cx: malignant transformation (extremely rare)