Epidermoid cysts

General

Aka:

Cholestatoma
Pearly tumor
Ectodermal inclusion cyst

Numbers

1% of intracranial tumors,

7% of CPA tumors.

Peak age of occurrence: 40 years.

No gender difference

Pathophysiology

Epidermoid vs cholesteatoma

Both are same but just in different places

Both near petrous part

Both arise from epithelium entrapped in an abnormal location

Features	Cholesteatoma	Epidermoid
Location	Extradural (middle ear)	Intradural

Origin

Displaced dorsal midline ectodermal cell rests trapped during neural tube closure between gestational weeks 3–5

Multipotential embryonic cell rests

Epithelial cell rests carried to the Cerebral-Pontine Angle with the developing otic vesicle

Epidermal cells displaced into CNS by

LP or
Repeated percutaneous cranial subdural taps

Localisation

Intradural: 90%

Cerebellopontine angle: 40-50%

3rd most common CPA mass, acoustic schwannomas>meningiomas>epidermoid cyst
Accounts for approximately 5-10% of all tumours in this region

Suprasellar cistern: 10-15%
Fourth ventricle: 17%
Middle cranial fossa
Interhemispheric: < 5%
Spinal (rare)

Extradural: 10%

Most within skull

Natural history

Chronic

Slow growth causing mass effect once large

Acute

Cyst haemorrhage and rupture causing chemical meningitis, headache, seizures, vasospasm and death

Malignant Transformation to Squamous cell carcinoma

Rare
OS 9 months
A deterioration in the absence of hydrocephalus and rapid tumour recurrence

Clinical presentation

May present as any mass lesion in the same location

CPA lesions can produce V, VII, or VIII neuropathies

Recurrent rupture of cyst contents → recurrent episodes of aseptic meningitis → hydrocephalus.

S&S of aseptic meningitis

Symptoms include fever and meningeal irritation.
CSF shows

Pleocytosis
Hypoglycorrhachia
Elevated protein
Negative cultures
Cholesterol crystals may be seen: amorphous birefringent appearance.

Mollaret’s meningitis

A rare variant of aseptic meningitis
Large cells in the CSF that resembling endothelial cells (which may be macrophages), which may be seen in some patients with epidermoid cysts

Imaging

General

Lobulated mass that fills and expand CSF spaces and exert a gradual mass effect

Encase nerve and vessels

Common feature of post fossa cyst → displacement of basilar artery away from pons

CT

Isodense to CSF:

Due to

Combination of cellular debris along with a high cholesterol content lower the density of epidermoids to approximately 0 HU, and can thus be identical in density to CSF, and look the same as an arachnoid cyst.

Calcification

A minority of cases (10-25%)
Rarely an epidermoid cyst may be hyperdense due to haemorrhage, saponification or high protein content ("white epidermoids"). The interhemispheric epidermoids are reported to have peripheral calcification.

They do not enhance and only very rarely demonstrate any enhancement of the wall.

Bone erosion in 33%

Common location

Uncommon locations

MRI

General

Epidermoids are often indistinguishable from arachnoid cysts or dilated CSF spaces on many MR sequences,

Due to epidermoid cystic contents are composed of keratin, cholesterol crystals, and desquamated epithelial cells suspended in a fluid medium that closely mimics the signal characteristics of cerebrospinal fluid. This composition makes the lesion fluid-like in behavior on conventional MRI sequences, resulting in hypo-intensity on T1 and hyper-intensity on T2, similar to CSF.

Except for DWI/ADC which helps to differentiate them.

Isointense to CSF
Higher signal compared to CSF around the periphery of the lesion is frequently seen
White epidermoid

Rare
High signal
Could be due to

High protein content
High lipid content (triglycerides, No cholesterol)

Can use fat suppression sq

Rare intralesional hemorrhage can also result in intrinsic high signal

T1 C+ (Gd)

Thin enhancement around the periphery may sometimes be seen
In the rare cases of malignant degeneration, enhancement becomes more pronounced

Isointense to CSF: 65%
Slightly hyperintense: 35%
Hypointense: Rare

Usually in the setting of the so-called white epidermoid (the term refers to the T1 appearance)

FLAIR

Often heterogeneous/dirty signal
Higher than CSF
Beware of flow artefact from CSF pulsation which can mimic this appearance

Useful for differentiation from arachnoid cysts

Arachnoid cyst shows T2 shine through
Epidermoid cyst shows restriction (T2 and ADC hyper intense) but unlike abscess or highly dense tumour it shows a ISOINTENSE ADC map

Images

T1+C

FLAIR

DWI

ADC

SWI

FIESTA

Histopathology

Macroscopic

White and pearly,
Can be smooth, lobulated, or nodular

Contents: creamy, waxy material

Microscopic

Cyst Wall are lined by

Stratified squamous epithelium, and
Contain

Keratin (from desquamated epithelium)
Cellular debris
Cholesterol

Cyst contents:

Liquid or
Flaky consistency.

Growth occurs at a linear rate like normal skin,

Unlike the exponential growth of true neoplasms

They tend to spread along normal cleavage planes and surround vital structures (cranial nerves, ICA…)
Bony destruction

Minority
Usually occurs with larger tumors

Rare malignant transformation → squamous cell cancer

In cases of repeated recurrences after multiple surgeries.

Treatment

Surgery

Curative
Symptoms are from mass effect
An STR to preserve neurological function is preferable to GTR if neurological morbidity is high
Cyst spillage of fat droplets causes chemical meningitis

Minimize spilling → may cause severe chemical meningitis (Mollaret’s meningitis, see above).
To reduce chemical meningitis

Intraoperative irrigation with hydrocortisone (100mg/L of LR) to reduce the risk of post-op communicating hydrocephalus.
Perioperative IV steroids and copious saline irrigation during surgery may provide similar results.

Recurrence

Mean 12 years from 1st resection

The tumor is not in the cyst wall → remove as much as possible but to leave capsule adherent to critical structures such as brainstem and blood vessels because

As the morbidity of removal is high
A small residual does not preclude satisfactory outcome.
In spite of adequate removal, it is not unusual to see persistent brainstem distortion on post-op imaging.

Post-op radiation is not indicated as the tumor is benign and does not prevent recurrence

Differential diagnosis

Dermoid cyst

Features	Intracranial Epidermoid Cysts	Intracranial Dermoid Cysts
Frequency	More common 0.5–1.5% of brain tumors	Rare 0.3% of brain tumors
Location	Off midline (CP angle)	Midline
Presentation	Later	Earlier
Origin	Congenital (arising from ectodermal inclusion during neural tube closure)	Embryonic ectoderm trapped in the closing neural tube between the 5th to 6th weeks of gestation
ㅤ	Acquired (post-surgical or post-traumatic implantation)	ㅤ
Lining	Simple skin cells, devoid of cutaneous-type adnexal structures Stratified squamous epithelium	Stratified squamous epithelium, containing epidermal appendages (hair follicles, sweat glands, sebaceous glands)
Contents	Keratin, cellular debris, cholesterol, occasional hair No dermal elements:	Same as epidermoid, plus hair and sebum Dermal elements: Hair follicles, sweat glands, sebaceous glands (secreting sebum)
Rupture	Less common	More common
Meningitis	May have recurrent aseptic meningitis, including mollarets meningitis	May have repeated bouts of bacterial meningitis
Associated anomalies	Tend to be isolated lesions	Associated with other congenital anomalies in up to 50% of cases
Imaging Appearance	Identical to the petrous apex and middle ear congenital cholesteatomas	Well-defined lobulated midline masses with low attenuation (fat density) on CT and high signal intensity on T1-weighted MR images
CT	Hypodense, slightly greater than CSF	Hypodense, similar to CSF
ㅤ	Bone erosion in 33%	Lobulated margins
ㅤ	No enhancement	Fine linear strands
ㅤ		No enhancement
T1W MRI	Isointense, same as CSF	Typically hyperintense, same as fat
ㅤ	Occasionally hyperintense around periphery;	No enhancement
ㅤ	No enhancement
T2W MRI	Isointense or hyperintense, same as CSF	Variable
FLAIR	Variable	Variable
DWI	Restricted diffusion, hyperintense to CSF	Restricted diffusion, hyperintense to CSF
Fat Saturation Sequence	Unchanged	High signal drops out
Local Findings	Insinuates between neurovascular structures	More mass effect
ㅤ	ㅤ	Associated abnormalities (e.g., Klippel-Feil, dermal sinus tract)
Enhancement After Contrast	Not specified in the provided information	Typically do not enhance
Associated abnormalities	Absent	May be present
Surgical resection	Difficult	Less difficult

Cholesterol granuloma

Feature	Epidermoid	Cholesteatoma	Cholesterol granuloma
Origin	Ectodermal cells in abnormal location (within CNS, intradural)	Ectodermal cells in abnormal location (within ear, extradural)	Chronic inflammatory cells surrounding cholesterol crystals (? from breakdown of RBC membranes)
Precursor	Usually congenital, occasionally acquired, e.g. after LP (p. 1601)	Usually acquired (following chronic infection ? due to epithelial cells from tympanic membrane), occasionally	Chronic middle ear infection or idiopathic hemotympanum
Symptoms	Vary depending on location	Congenital chronic hearing loss, ear drainage, pain, or numbness around ear	Usually involve vestibular or cochlear dysfunction
Imaging (may not reliably distinguish among these)	CT: low density; no enhancement; bone erosion in only 33% MRI: TIWI: intensity slightly>CSF; T2Wl: tumor & CSF similar high intensity	CT: low density; no enhancement; bone erosion in only 33% MRI: TIWI: intensity slightly>CSF; T2Wl: tumor & CSF similar high intensity	CT: homogeneous & isodense; rim enhancement; extensive destruction of petrous bone MRI: increased signal on both TIWI and T2Wl
Gross appearance	Pearly white	Pearly white	Brown (from hemosiderin)
Microscopic pathology	Hyperkeratotic cyst lined with stratified squamous epithelium	Hyperkeratotic cyst lined with stratified squamous epithelium	Fibroblastic proliferation, hemosiderin-laden macrophages, cholesterol clefts, giant cell reaction
Ideal treatment	Aggressive near-total excision	Aggressive near-total excision	Subtotal resection followed by drainage & restoration of pneumatization

Adamantinomatous Craniopharyngioma

Have similar histology

Epidermoid cyst have

Cholesterol components
Keratin components

Arachnoid cyst

Characteristic	Arachnoid Cvst	Epidermoid
CIS density	CSF	Slightly higher than CSF
Margins	Smooth	Scalloped
Calcification	No	25%
Blood vessel involvement	Deviates	Insinuates between vessels
Intrathecal contrast	May take up but can be delayed	No uptake, defines borders
Characteristic on MR sequence sensitive to CSF pulsation (steady state free precession)	Pulsates	Does not pulsate
Diffusion	Dark	Bright
ADC	Increased	Decreased
FLAIR	Dark	Bright