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Both of these tumor types are benign. They are considered to be "developmental", since they result from a failure of migration of ectodermal cells during embryonic development. These cells are then trapped within the growing Brain and are present at birth.

These slow growing tumors generally occur in the following locations:

  • Skull
  • Suprasellar - commonly produce visual changes
  • Sylvian fissure - may present with seizures
  • Cerebellopontine Angle - may produce facial pain, numbness, or weakness and hearing loss
  • Scalp
  • Spinal canal

Epidermoid Tumor

Epidermoid tumors (often called "Pearly Tumors" because of their appearance at surgery - see Figures 2A-2C) account for 1% of intracranial tumors and approximately 7% of Cerebellar Pontine Angle (Posterior Cranial Fossa and Skull Base) tumors.


Symptoms usually occur late in the course of the disease process since growth is slow and compression, distortion and stretching of the Brain, Brain Stem and/or Cranial Nerves often is well tolerated until some critical point is reached past which these structures can no longer accommodate. The symptoms (see "Locations" above) will manifest depending on the location of the lesion. Cranial Nerve symptoms are fairly common for those tumors that occur in the Posterior Cranial Fossa and Suprasellar.


They are diagnosed by MRI and CT scans. They are often in the same location as Acoustic Neuromas. However, their Neuroimaging characteristics are quite different. Epidermoid Tumors do not enhance with contrast, and often, are indistinct to the point of being unappreciated and undiagnosed. They can be confused with Arachnoid Cysts occurring in the same location. Sophisticated MRI scanning techniques and experienced specialists can usually differentiate between these two entities.

Figure 1A (Top Left): MRI Scan (Coronal View) Right Cerebellar Pontine Angle (CPA) Epidermoid (Horizontal Arrow) demonstrating compression, distortion and displacement of the Brain Stem (Vertical Arrow).

Figure 1B (Top Right): MRI Scan (Axial View-Same Patient). The mass effect (Arrow) of the Epidermoid Tumor on the Brain Stem and Cerebellum is demonstrated.

Figure 1C (Left): MRI Scan (Sagittal View-Same Patient). The Epidermoid Tumor shares some characteristics as an Arachnoid Cyst (Arrow).



Surgical resection is the treatment of choice. These tumors have a tendency to have a capsule that is densely attached to surrounding structures including the tiny, delicate vessels of the Brain Stem and Cranial Nerves. This can make complete capsule resection quite difficult, if not impossible, without causing serious injury. In some patients it may be necessary to leave remnants of the capsule behind, which increases the risk of recurrence (See Figures 2A-C).

Figure 2A (Top Left): Operative Photo Right Retromastoid Craniotomy for CPA Epidermoid (Same Patient as Figure 1). The tumor is enclosed within the Subarachnoid Space where Cerebrospinal Fluid circulates as well. The Arachnoid (Curved Arrow) is a thin, filamentous membrane.

Figure 2B (Top Right): Operative Photo Part of the tumor has been removed. The "Pearly Tumor" appearance is well demonstrated as it inserts itself into the interstices around and between the nerves, vessels, Cerebellum (Curved Arrow) and Brain Stem (Straight Arrow).

Figure 2C (Left): Operative Photo. Most of the tumor has been removed. Small pieces remain attached to the Arachnoid membrane that is attached to vital small vessels of the Brain Stem (Center Arrow).

Radiation Therapy

Radiation Therapy is not an option for these tumors, since the tumor is not made up of cells that are dividing (dividing cells - as occurs in Cancer - are the ones that are susceptible to radiation), and will not respond. Radiation therapy does prevent recurrence of Epidermoid Tumors.


Dermoid Tumors represent 0.3% of Brain tumors. Dermoids tend to be located near the midline in contrast to Epidermoid Tumors which are more often laterally placed such as in the Cerebellar Pontine Angle (CPA). Dermoids also tend to be associated with other congenital abnormalities.


Symptoms are usually dependent on the site of origin of the tumor and consequent to the neural structures that are compromised. One problem that is unique to Dermoid Tumors, although an infrequent occurrence is a condition known as Aseptic (also known as non-infectious) Meningitis. This is unusual as an initial problem that brings the patient to the attention of Neurosurgeons; however, this can occur as a result of rupture of the cyst and spillage of its very irritating contents.


The diagnosis is usually made with MRI scanning.


Surgical removal is the only treatment option and is usually curative. Care must be taken not to spill the contents of an Intracranial or Intraspinal Dermoid "cyst" since it can incite in a severe inflammatory response known as Aseptic Meningitis.

Figure 4: Operative Photo
Orbital Dermoid (Same as Figure 3)

The capsule (Curved Arrow) of the Dermoid Tumor has been carefully separated from the delicate structures of the Orbit (muscles and nerves) and then opened to permit access to its contents. The contents (Vertical Arrow) are quite irritating chemically and spillage must be avoided. Here this is done by placing special pads (white material) around the lesion. Following this the contents are emptied and the remaining capsule is separated from the adjacent structures and entirely removed.

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This page last edited on 2/19

All content ©2022 by Neurosurgical Consultants, P.A.
Author, Martin L. Lazar, MD, FACS
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