Origin: defect in cleavage of neural tissue from cutaneous ectoderm during closure of neural tube in 5th week of fetal life (early inclusion results in midline lesion, later inclusion results in more lateral location)
Frequency: dermoid÷epidermoid = 1÷3 to 1÷10
Location: most commonly in midline (anterior fontanelle, glabella, nasion, vertex, subocciput) >frontotemporal >parietal location
Affected sutures: frontozygomatic, sphenofrontal, sphenosquamosal, squamosal, coronal, lambdoid, parietomastoid
- ± external skin ostia and deep sinus tracts
- angiographically avascular
- NO contrast enhancement internally (DDx to teratoma)
- rare peripheral rim enhancement ← perilesional inflammation / infection
Cx:
- Chemical / aseptic meningitis (rare)
- Squamous cell carcinoma (rare)
Path: ectoderm + skin elements = pilosebaceous mass of squamous epithelial cells + mesodermal cells (hair follicles, sweat glands and sebaceous glands)
Growth: desquamation of epithelial cells + glandular secretion → faster growth than epidermoids
Incidence: 1% of all intracranial tumors
Age:<30 years (appears in adulthood due to slow growth); M <F
Location:
- spinal canal (most common): extra- / intramedullary in lumbosacral region
- posterior fossa within vermis / 4th ventricle (predilection for midline)
- posterior to superior orbital fissure, may be associated with bone defect
- sellar + parasellar region
- nasion ± sinus tract up to foramen cecum
Risk: CNS infection
- bouts of chemical / bacterial meningitis possible
- thick-walled inhomogeneous mass with focal areas of fat
- mural / central calcifications / bone (possible)
- may have sinus tract to skin surface (dermal sinus) if located in midline at occipital / nasofrontal region
- fat-fluid level if cyst ruptures into ventricles, fat droplets in subarachnoid space
CT:
- variable appearance ± areas of low attenuation due to lipid component
MR:
Dermoid Cyst versus Teratoma
|
- variointense on T1WI (hyperintense with contents of liquefied cholesterol products)
- curvilinear regions of low SI on T1WI + T2WI (= hair)
- shortened T1 + T2 relaxation times (= fat)
- suppressed fat signal on fat-suppressed images
Path: ectoderm WITHOUT skin elements = “pearly tumor” = well-defined solid lesion with glistening irregular nodular surface; lamellar cyst contents consists of soft flaky desquamated keratinaceous debris rich in cholesterol + triglycerides = primary / congenital cholesteatoma
Incidence: 0.2–1.8% of all primary intracranial neoplasms; most common congenital intracranial tumor
Histo: tumor lined by simple stratified cuboidal squamous epithelium; surrounded by thin band of collagenous connective tissue
Growth: extremely slow linear growth resulting from desquamation of epithelial cells
Age: 10–60 years, peak age in 4th–5th decade (slow tumor expansion over decades thus becoming symptomatic in adulthood); M÷F = 1÷1
- facial pain
- cranial nerve palsies with CP angle epidermoid (50%)
- visual abnormality + endocrinologic disturbance (eg, diabetes insipidus) with suprasellar epidermoid
- hydrocephalus with suprasellar epidermoids
- chemical meningitis (← leakage of tumor contents into subarachnoid space) with middle cranial fossa epidermoids
Location:
- cerebellopontine angle (40%, account for 5% of CP angle tumors)
- suprasellar region, perimesencephalic cisterns (14%)
- in ventricles, brainstem, brain parenchyma
- pineal region (3–4%): peak age in 3rd decade
- skull vault
Site: midline / paramidline; intradural (90%) / extradural; transspatial growth (= extension from one into another intracranial space)
- soft lesion insinuating into adjacent brain parenchyma:
- conforming to + molding itself around brain surfaces
- intimately surrounding vessels + cranial nerves rather than displacing them (limited resectability)
- little mass effect, no edema / hydrocephalus
- may be associated with dermal sinus tract at occipital / nasofrontal region if midline in location
CT:
- typically lobulated round homogeneous mass with density similar to CSF (between water and –20 HU)
- occasionally hyperdense due to high protein content, saponification of keratinaceous debris, prior hemorrhage into cyst, ferrocalcium / iron-containing pigment, abundance of PMNs
- bony erosion with sharply defined well-corticated margins
- peripheral calcifications (in 25%)
MR:
- lamellated onionskin appearance with septations (layer-on-layer accretion of desquamated material)
- “black epidermoid” (majority) = SI similar to CSF:
- heterogeneously hypointense lesion on T1WI
- hyperintense on T2WI
Cause: cholesterol in solid crystalline state + keratin within tumor + CSF within tumor interstices
- “white epidermoid” (rare) = SI similar to fat:
- hyperintense on T1WI
- iso- to hyperintense on T2WI
Cause: triglycerides + polyunsaturated fatty acids
- SI similar to calcium = hypointense on T2WI (very rare)← peripheral calcifications, low hydration, viscous secretion, paramagnetic iron-containing pigment
- incomplete saturation on FLAIR = hyperintense relative to CSF (DDx: arachnoid cyst)
- lesion very hyperintense on DWI
- signal intensity suppression on fat-suppressed sequence (DDx: lipoma exhibits more suppression)
Cisternography:
- papillary / frondlike surface with contrast material extending into tumor interstices
Rx: surgical resection (complicated by adherence to surrounding brain + cranial nerves, spillage of cyst contents with chemical meningitis, CSF seeding + implantation)
DDx: arachnoid cyst (smooth surface, earlier diffusion, equal to CSF), lipoma, cystic schwannoma, adenomatoid tumor, atypical meningioma, chondroma, chondrosarcoma, chordoma, calcified neurogenic tumor, teratoma, calcified astrocytoma, ganglioglioma