Differential Diagnosis for Epidermoid Cyst in the Left CP Angle Cisterns

• Single most likely diagnosis:

  • Epidermoid cyst: This is the most likely diagnosis given the location and description. Epidermoid cysts are benign, slow-growing tumors that can occur in the central nervous system, often found in the cerebellopontine (CP) angle. They are usually congenital and result from the inclusion of ectodermal elements during neural tube closure.

• Other Likely diagnoses:

  • Arachnoid cyst: These are fluid-filled sacs that can occur in the CP angle and may resemble epidermoid cysts on imaging. However, they typically contain CSF and do not have the same solid components as epidermoid cysts.
  • Meningioma: Although less common in the CP angle, meningiomas can occur here and may present similarly to epidermoid cysts. They are usually more solid and may have dural tails on imaging.
  • Neuroenteric cyst: These are rare congenital abnormalities that can occur in the CP angle, containing mucoid material. They might be considered if there's a suspicion of a cystic lesion with a different content than CSF.

• Do Not Miss diagnoses:

  • Acoustic neuroma (Vestibular schwannoma): Although typically more solid and enhancing, a small acoustic neuroma could be considered, especially if there's any suspicion of hearing loss or cranial nerve deficits. Missing this diagnosis could lead to significant morbidity if left untreated.
  • Cystic metastasis: Rarely, metastatic lesions can present as cystic masses in the CP angle. Given the potential for aggressive disease, this diagnosis should not be missed, especially in patients with a known history of cancer.

• Rare diagnoses:

  • Dermoid cyst: While similar to epidermoid cysts, dermoid cysts contain more complex elements like hair, teeth, or sebaceous material. They are less common than epidermoid cysts and can be considered if there are unusual contents within the cyst.
  • Colloid cyst: Typically found in the third ventricle, it's rare for colloid cysts to occur in the CP angle. However, if a cystic lesion with a high protein content is suspected, this could be a rare consideration.
  • Choroid plexus cyst: These are benign cysts that usually occur within the choroid plexus of the ventricles but could theoretically be considered if a cystic structure is seen in an unusual location like the CP angle, though this would be exceedingly rare.