dermoid cysts are slow growing , congenital masses that are encompassed by a capsule consisting of both epidermal and dermal derivatives . they are thought to arise from the totipotent ectodermal cells that fail to separate from the developing neural tube . the posterior fossa is the most common location for dermoid cysts , accounting for 0.03%0.7% of all intracranial tumors . although they are nonneoplastic , they can present with signs and symptoms secondary to mass effect on the brain , cranial nerves and vessels , aseptic meningitis , hydrocephalus , intracranial hypertension , seizures , and visual loss . surgery is the treatment of choice , and the goal is resection of the entire cyst to avoid regrowth . dermoid cysts are usually found in the midline . in 1891 , hans chiari published a series on hindbrain herniations based on autopsy findings where he found a distinct form of malformation exclusively in patients with myelomeningocele . chiari ii malformations were initially thought of as being the caudal displacement of the cerebellar vermis , brainstem , and fourth ventricle . however , it is now known that they represent a complex malformation involving both supratentorial and infratentorial components , in addition to the skull and vertebral elements . coexistence of a chiari ii malformation and posterior fossa dermoid has , to the best of our knowledge , never been reported before . herein , we report the incidental finding of a dermoid cyst found during a chiari ii malformation . a newborn with myelomeningocele ( diagnosed by elevated maternal serum alpha - fetoprotein at 7.5 months , confirmed by ultrasound ) was born at 39 weeks through c - section . on day 2 of life , stridor was noted on day of life ( dol ) 9 , and a ventriculoperitoneal shunt was placed on dol 10 . the shunt was removed , and an external ventricular drain was placed to assure adequate cerebrospinal fluid diversion before potential chiari ii decompression . three days later , we were unable to wean the patient 's ventilator , despite a low setting of the ebola virus disease . deep to the choroid plexus , desquamated epithelium , and hair were observed [ figure 2 ] . the patient did not have significant improvement in their stridor and went on to have a tracheostomy placed , 3 weeks later . at 1-year follow - up , the patient was tolerating tube feeds and was gaining weight . follow - up scan at 10 years of age showed no signs of posterior fossa dermoid [ figure 3 ] . preoperative sagittal magnetic resonance imaging noting hyperintensity at outlet of ectopically placed fourth ventricular outlet operative image of the posterior fossa noting the fourth ventricular outlet . note the dermoid located near the ectopic choroid plexus of the fourth ventricle follow - up sagittal magnetic resonance imaging at 10 years of age showing no sign of posterior fossa dermoid an intracranial dermoid cyst is a rare entity accounting for less than 1% of all intracranial tumors in children . dermoids are composed of a thick fibrous capsule , which contains stratified squamous epithelium and are derived from ectodermal cell lineages only . the fluid within these cysts is composed of lipid metabolites , cholesterol crystals , and whorls of hair . the high density of cholesterol within a dermoid cyst is associated with t1-weighted imaging ( wi ) hyperintensity and t2-wi hypointensity . the solid component of the dermoid may lead to decreased diffusion in comparison to purely cystic lesions . lead to dermoid particles being dispersed into the subarachnoid space , and the involvement of the subarachnoid space and/or the meninges can result in vasospasm , hydrocephalus , or aseptic meningitis . therefore , it is important to suspect such lesions in the posterior fossa , even in patients with chiari ii malformation .
dermoid cysts are rare lesions , particularly in children . chiari 
 ii malformations are seen in patients with myelomeningocele . here , we present a child with chiari ii malformation who , during a chiari ii decompression , was found to have a dermoid cyst . to the best of our knowledge , 
 this is the first such case ever reported .