a 4-year - old female child presented with her third episode of fever , headache , and vomiting .
her first such episode was at 3 years and 2 months of age for which she was treated elsewhere as  pyogenic meningitis  with antibiotics after a cerebrospinal fluid ( csf ) study which was culture negative .
since she had recurrent meningitis , computed tomography ( ct ) of the head with contrast was done which was initially reported as 
 her complement levels ( c3 and c4 ) and immunoglobulin ( including igg subclass ) assays were normal and her retroviral status and vasculitis workup were negative .
she was given pneumococcal vaccine and was discharged after which her third similar episode occurred .
csf leak was thought of and ct myelocisternography was done which did not reveal any bony defect .
reevaluation of the old ct showed a hypodense ( 2 - 20 hounsfield unit ) cyst seen in front of the brain stem , with minimal flattening of the anterior surface of medulla which was initially missed [ figure 1 ] .
magnetic resonance imaging ( mri ) with spectroscopy confirmed the presence of an epidermoid cyst in the premedullary cistern [ figure 2 ] with a prominent lipid peak .
she underwent a near - total excision of the lesion and histopathology confirmed an epidermoid cyst .
computed tomography shows a hypodense ( 2 - 20 hounsfield unit ) cyst seen in front of the brain stem in the premedullary cistern lifting the basilar artery ( arrow ) , with flattening of the anterior surface of medulla ( arrow head ) ( a ) a 30  23  39 mm well - defined t1 hypointense lesion ( white arrow ) , with flattening of the anterior surface of medulla ( arrow head ) .
( b ) its t2 hyperintense occupying the premedullary and prepontine cistern displacing medulla oblongata and inferior part of pons posteriorly .
( c ) flair images differentiate epidermoids from arachnoid cysts demonstrating lesion to be hyperintense to csf .
( d ) diffusion - weighted imaging show high signal intensity suggesting restricted diffusion with corresponding .
recurrent meningitis is defined as two or more episodes of meningitis separated by a period of complete resolution of signs , symptoms , and laboratory findings .
aseptic meningitis can be recurrent and is characterized by noninfective serous inflammation of the meninges .
it presents as recurring bouts of fever , meningism , pleocytosis , and a failure to culture organisms from the csf .
the reaction is sudden and striking but of short duration , and is often preceded and followed by symptom free intervals .
epidermoid and dermoid cysts can cause recurrent , episodic aseptic meningitis by rupturing cyst contents into the subarachnoid space , which is thought to result in chemical irritation .
epidermoid cysts originate from the inclusion of epidermal components within the neuraxis during the embryonic stage and can be located intracranially or intraspinally and present in the third or fourth decade of life .
dermoids are midline often accompanied by persistent defects in the closure of the overlying bone and skin , while epidermoids are found more often in lateral positions , such as the cerebellopontine angles .
the pathological reaction to the irritants ranges from mild leptomeningitis to widespread granulomatous meningitis , ependymitis , and posterior radiculitis . since chemical and bacterial meningitis may coexist , it is safer to start antibiotic therapy initially since the spinal fluid profiles in bacterial and chemical meningitis are similar .
the exceptions are a csf white blood cell count > 7500/l and a glucose level of < 10mg / dl that are not found in any case of chemical meningitis .
patients with chemical meningitis usually do not present with coma , new focal neurological findings , or new onset of seizures and they rarely have temperatures > 39.4c bacterial meningitis in association with these tumors is most commonly related to a coexisting dermal sinus tract and the most common organism is staphylococcus aureus .
the literature search identified 24 cases of recurrent meningitis associated with dermoid and epidermoid cysts .
our case was unique because of its relatively early and rare presentation with aseptic meningitis and to highlight the fact that these lesions can be missed in cursory ct reading unless specifically looked for .
identification of these lesions is important since patients can be spared expensive workup for recurrent meningitis and they can lead a symptom - free life once total excision is performed .
 aseptic meningitis is characterized by noninfective serous inflammation of the meninges . 
 it can occur in a recurrent fashion when associated with dermoid and epidermoid cysts due to rupture of cyst contents into subarachnoid space resulting in aseptic chemical meningitis . 
 bacterial meningitis in association with these tumors is commonly related to a coexisting dermal sinus tract and the most common organism is staphylococcus aureus . 
Introduction
Case Report
Discussion