Intracranial epidermoid cyst

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Intracranial epidermoid cysts are relatively common congenital lesions which account for about 1% of all intracranial tumours. They result from inclusion of ectodermal elements during neural tube closure, and typically present in middle age due to mass effect on adjacent structures. Their content, derived from desquamated epithelial cells, mimics CSF on CT and MRI, with the exception of DWI which demonstrates restricted diffusion. Management is surgical and prognosis is good.

Epidemiology

Although predominantly congenital, epidermoid cysts are usually very slow growing and as such take many years to present. Typically patients are between 20 and 40 years of age ⁶. There may be increased prevalence in males, although this is not found in all series ^5-6.

Epidermoid cysts account for approximately 1% of all intracranial tumours ^2,8.

An uncommon association exists with anorectal anomalies, sacral anomalies and ~~pre-sacral~~presacral mass, and is known as the Currarino triad ⁵.

Clinical presentation

Signs and symptoms of epidermoid cysts are due to gradual mass effect, with presentation including ⁴:

headaches: most common
cranial nerve deficits
cerebellar symptoms
seizures
raised intracranial ~~presure~~pressure

Recurrent aseptic meningitis is uncommon but recognised, similar to the less common dermoid cyst ⁴.

Pathology

Epidermoid cysts may be congenital (most common, arising from ectodermal inclusion during neural tube closure ⁸) or acquired (post surgical or post traumatic implantation). Pathologically, intracranial epidermoid cysts are identical to the petrous apex and middle ear congenital cholesteatomas. They differ from dermoid cysts~~which~~ which have both epidermal and skin appendages such as hair and sebaceous cysts and mature teratomas which have all three layers.

They have a thin capsule which is made of a thin layer of squamous epithelium, which macroscopically is white and pearly, and may be smooth, lobulated or nodular. Internal cystic components are often filled with desquamated epithelial keratin and cholesterol crystals; grossly appearing as a creamy, waxy material. It should be noted that some authors contest that epidermoid cysts are along a spectrum which includes cystic (adamantinomatous) craniopharyngiomas, which have some histological similarities ⁷. Cholesterol and keratin components account for their distinct imaging characteristics ².

Location

~~intra dural~~intradural: 90%
- cerebellopontine angle: 40-50% ^2,8
  - third most common cerebellopontine angle mass, after acoustic schwannomas and meningiomas, and accounts for approximately 5-10% of all tumours in this region ^2,4,8.
- suprasellar cistern: 10-15% ⁸
- fourth ventricle: ~17% ⁸
- middle cranial fossa
- interhemispheric
- spinal (rare)
~~extra dural~~extradural: 10%⁸
- most within skull

Radiographic features

~~On CT intracranial~~Intracranial epidermoid cysts appear as lobulated lesions that fill and expand CSF spaces and exert gradual mass effect, insinuating between structures and encasing adjacent nerves and vessels. A common feature of posterior fossa cysts is displacement of thebasilar artery ~~away~~ away from thepons.

CT

The 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~~

Calcification is seen in a minority of cases (10-25% ⁸), and rarely an epidermoid cyst may be hyperdense due to haemorrhage, saponification or high protein content ("white epidermoids").

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

MRI

Appearances on MR are similar to those on CT, with epidermoids often being indistinguishable from arachnoid cysts or dilated CSF spaces on many sequences.

T1
- usually isointense to CSF
- higher signal compared to CSF around the periphery of the lesion is frequently seen
- rarely they can be of high signal and are known as white epidermoids
- rare intralesional haemorrhage 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
T2
- usually isointense to CSF (65%)
- slightly hyperintense (35%)
- rarely hypointense, usually in the setting of the so called white epidermoid (the term refers to the T1 appearance) ²
FLAIR
- often heterogeneous/dirty signal; higher than CSF
- beware of flow artefact~~from~~ from CSF pulsation which can mimic this appearance
DWI: useful for differentiation from arachnoid cysts due to increased signal (due to a combination to true restricted diffusion and T2 shine through) which is not seen with arachnoid cysts

Treatment and prognosis

Surgical excision is the treatment of choice if symptomatic. However, complete resection is difficult as not all tissue can be removed, especially from around cranial nerves and vessels. Recurrence is therefore not uncommon, although growth is typically slow and many years can elapse without new symptoms.

Differential diagnosis

The differential for an epidermoid cyst include:

CSF collections, e.g. arachnoid cyst or mega cisterna magna
- less lobulated
- follows CSF on all sequences, including FLAIR and DWI
dermoid cyst
- often fat density due to sebum
inflammatory cyst, e.g. neurocysticercosis
- smaller, but may be multiple
- may enhance peripherally
- may have associated oedema
- usually no restricted ~~disffusion~~diffusion
cystic ~~tumour~~tumours, e.g. acoustic schwannoma or craniopharyngioma
- solid enhancing component is usually identifiable
neurenteric cyst

-<p><strong>Intracranial epidermoid cysts</strong> are relatively common congenital lesions which account for about 1% of all intracranial tumours. They result from inclusion of ectodermal elements during neural tube closure, and typically present in middle age due to mass effect on adjacent structures. Their content, derived from desquamated epithelial cells, mimics CSF on CT and MRI, with the exception of DWI which demonstrates restricted diffusion. Management is surgical and prognosis is good. </p><h4>Epidemiology</h4><p>Although predominantly congenital, epidermoid cysts are usually very slow growing and as such take many years to present. Typically patients are between 20 and 40 years of age <sup>6</sup>. There may be increased prevalence in males, although this is not found in all series <sup>5-6</sup>.</p><p>Epidermoid cysts account for approximately 1% of all intracranial tumours <sup>2</sup>. </p><p>An uncommon association exists with anorectal anomalies, sacral anomalies and pre-sacral mass, and is known as the <a href="/articles/currarino-triad">Currarino triad</a> <sup>5</sup>. </p><h4>Clinical presentation</h4><p>Signs and symptoms of epidermoid cysts are due to gradual mass effect, with presentation including <sup>4</sup>:</p><ul>
+<p><strong>Intracranial epidermoid cysts</strong> are relatively common congenital lesions which account for about 1% of all intracranial tumours. They result from inclusion of ectodermal elements during neural tube closure, and typically present in middle age due to mass effect on adjacent structures. Their content, derived from desquamated epithelial cells, mimics CSF on CT and MRI, with the exception of DWI which demonstrates restricted diffusion. Management is surgical and prognosis is good. </p><h4>Epidemiology</h4><p>Although predominantly congenital, epidermoid cysts are usually very slow growing and as such take many years to present. Typically patients are between 20 and 40 years of age <sup>6</sup>. There may be increased prevalence in males, although this is not found in all series <sup>5-6</sup>.</p><p>Epidermoid cysts account for approximately 1% of all intracranial tumours <sup>2,8</sup>. </p><p>An uncommon association exists with anorectal anomalies, sacral anomalies and presacral mass, and is known as the <a href="/articles/currarino-triad">Currarino triad</a> <sup>5</sup>. </p><h4>Clinical presentation</h4><p>Signs and symptoms of epidermoid cysts are due to gradual mass effect, with presentation including <sup>4</sup>:</p><ul>
~~-<li>raised intracranial presure</li>~~
-</ul><p>Recurrent aseptic meningitis is uncommon but recognised, similar to the less common <a href="/articles/intracranial-dermoid-cyst-1">dermoid cyst</a> <sup>4</sup>.</p><h4>Pathology </h4><p>Epidermoid cysts may be congenital (most common) or acquired (post surgical or post traumatic implantation). Pathologically, intracranial epidermoid cysts are identical to the <a href="/articles/petrous-apex">petrous apex</a> and <a href="/articles/middle-ear">middle ear</a> <a href="/articles/congenital-cholesteatoma">congenital cholesteatomas</a>. They differ from <a href="/articles/intracranial-dermoid-cyst-1">dermoid cysts </a>which have both epidermal and skin appendages such as hair and sebaceous cysts and <a href="/articles/intracranial-teratoma">mature teratomas</a> which have all three layers. </p><p>They have a thin capsule which is made of a thin layer of squamous epithelium, which macroscopically is white and pearly, and may be smooth, lobulated or nodular. Internal cystic components are often filled with desquamated epithelial keratin and cholesterol crystals; grossly appearing as a creamy, waxy material. It should be noted that some authors contest that epidermoid cysts are along a spectrum which includes cystic (adamantinomatous) <a href="/articles/craniopharyngioma">craniopharyngiomas</a>, which have some histological similarities <sup>7</sup>. Cholesterol and keratin components account for their distinct imaging characteristics <sup>2</sup>.</p><h5>Location</h5><ul>
~~-<li>intra dural: 90% <ul>~~
-<li>cerebellopontine angle: 40-50% <sup>2</sup><ul><li>third most common <a href="/articles/cerebellopontine-angle-mass">cerebellopontine angle mass</a>, after <a href="/articles/acoustic-schwannoma">acoustic schwannomas</a> and <a href="/articles/meningioma">meningiomas</a>, and accounts for approximately 5-10% of all tumours in this region <sup>2,4</sup>. </li></ul>
+<li>raised <a href="/articles/intracranial-pressure">intracranial pressure</a>
+</li>
+</ul><p>Recurrent aseptic meningitis is uncommon but recognised, similar to the less common <a href="/articles/intracranial-dermoid-cyst-1">dermoid cyst</a> <sup>4</sup>.</p><h4>Pathology </h4><p>Epidermoid cysts may be congenital (most common, arising from ectodermal inclusion during neural tube closure <sup>8</sup>) or acquired (post surgical or post traumatic implantation). Pathologically, intracranial epidermoid cysts are identical to the <a href="/articles/petrous-apex">petrous apex</a> and <a href="/articles/middle-ear">middle ear</a> <a href="/articles/congenital-cholesteatoma">congenital cholesteatomas</a>. They differ from <a href="/articles/intracranial-dermoid-cyst-1">dermoid cysts</a> which have both epidermal and skin appendages such as hair and sebaceous cysts and <a href="/articles/intracranial-teratoma">mature teratomas</a> which have all three layers. </p><p>They have a thin capsule which is made of a thin layer of squamous epithelium, which macroscopically is white and pearly, and may be smooth, lobulated or nodular. Internal cystic components are often filled with desquamated epithelial keratin and cholesterol crystals; grossly appearing as a creamy, waxy material. It should be noted that some authors contest that epidermoid cysts are along a spectrum which includes cystic (adamantinomatous) <a href="/articles/craniopharyngioma">craniopharyngiomas</a>, which have some histological similarities <sup>7</sup>. Cholesterol and keratin components account for their distinct imaging characteristics <sup>2</sup>.</p><h5>Location</h5><ul>
+<li>intradural: 90% <ul>
+<li>cerebellopontine angle: 40-50% <sup>2,8</sup><ul><li>third most common <a href="/articles/cerebellopontine-angle-mass">cerebellopontine angle mass</a>, after <a href="/articles/acoustic-schwannoma">acoustic schwannomas</a> and <a href="/articles/meningioma">meningiomas</a>, and accounts for approximately 5-10% of all tumours in this region <sup>2,4,8</sup>. </li></ul>
+</li>
+<li>suprasellar cistern: 10-15% <sup>8</sup>
+</li>
+<li>fourth ventricle: ~17% <sup>8</sup>
~~-<li>suprasellar cistern</li>~~
~~-<li>fourth ventricle</li>~~
~~-<li>extra dural: 10%<ul><li>most within skull</li></ul>~~
+<li>extradural: 10% <sup>8</sup><ul><li>most within skull</li></ul>
-</ul><h4>Radiographic features</h4><h5>CT</h5><p>On CT intracranial epidermoid cysts appear as lobulated lesions that fill and expand CSF spaces and exert gradual mass effect, insinuating between structures. A common feature of posterior fossa cysts is displacement of the <a href="/articles/basilar-artery">basilar artery</a> away from the <a href="/articles/pons">pons</a>.</p><p>The 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 <a href="/articles/arachnoid-cyst">arachnoid cyst</a>. Calcification is seen in a minority of cases, and rarely an epidermoid cyst may be hyperdense due to haemorrhage, saponification or high protein content. </p><p>They do not enhance, and only very rarely demonstrate any enhancement of the wall. </p><h5>MRI</h5><p>Appearances on MR are similar to those on CT, with epidermoids often being indistinguishable from <a href="/articles/arachnoid-cyst">arachnoid cysts</a> or dilated CSF spaces on many sequences.</p><ul>
+</ul><h4>Radiographic features</h4><p>Intracranial epidermoid cysts appear as lobulated lesions that fill and expand CSF spaces and exert gradual mass effect, insinuating between structures and encasing adjacent nerves and vessels. A common feature of posterior fossa cysts is displacement of the <a href="/articles/basilar-artery">basilar artery</a> away from the <a href="/articles/pons">pons</a>.</p><h5>CT</h5><p>The 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 <a href="/articles/arachnoid-cyst">arachnoid cyst</a>. </p><p>Calcification is seen in a minority of cases (10-25% <sup>8</sup>), and rarely an epidermoid cyst may be hyperdense due to haemorrhage, saponification or high protein content ("<a href="/articles/white-epidermoid">white epidermoids</a>"). </p><p>They do not enhance, and only very rarely demonstrate any enhancement of the wall. </p><h5>MRI</h5><p>Appearances on MR are similar to those on CT, with epidermoids often being indistinguishable from <a href="/articles/arachnoid-cyst">arachnoid cysts</a> or dilated CSF spaces on many sequences.</p><ul>
~~-<li>beware of flow <a href="/articles/mri-artifacts">artefact </a>from CSF pulsation which can mimic this appearance</li>~~
+<li>beware of flow <a href="/articles/mri-artifacts">artefact</a> from CSF pulsation which can mimic this appearance</li>
~~-<a href="/articles/intracranial-dermoid-cyst-1">dermoid cyst</a><ul><li>often fat density due to sebum </li></ul>~~
+<a href="/articles/intracranial-dermoid-cyst-1">dermoid cyst</a><ul>
+<li>often fat density due to sebum </li>
+<li>typically located along the midline</li>
+</ul>
~~-<li>usually no restricted disffusion</li>~~
+<li>usually no restricted diffusion</li>
-<li>cystic tumour, e.g. <a href="/articles/acoustic-schwannoma">acoustic schwannoma</a> or <a href="/articles/craniopharyngioma">craniopharyngioma</a><ul><li>solid enhancing component is usually identifiable</li></ul>
+<li>cystic tumours, e.g. <a href="/articles/acoustic-schwannoma">acoustic schwannoma</a> or <a href="/articles/craniopharyngioma">craniopharyngioma</a><ul><li>solid enhancing component is usually identifiable</li></ul>
~~-</ul><p> </p>~~
+</ul>

References changed:

8. Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239 (3): 650-64. <a href="http://radiology.rsna.org/content/239/3/650.full">Radiology (full text)</a> - <a href="http://dx.doi.org/10.1148/radiol.2393050823">doi:10.1148/radiol.2393050823</a> - <a href="http://www.ncbi.nlm.nih.gov/pubmed/16714456">Pubmed citation</a><span class="ref_v3"></span>

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