A 16-year-old female presented with chronic headaches for 5 years with neurological examination revealing no sensory or motor deficits. The patient was referred for magnetic resonance imaging of the brain that showed lobulated lesion appearing hypointense on T2-weighted/fluid-attenuated inversion recovery (FLAIR) images and hyperintense on T1-weighted images in the midline anterior to the pontomedullary junction and extending from the midline into the left cerebellopontine angle [Figures –]. The lesion measured 2.8 cm × 1.3 cm × 1.5 cm and showed no obvious enhancement on the administration of contrast. There was no diffusion restriction on diffusion-weighted (DW) images while magnetic resonance spectroscopy (MRS) exhibited an N-acetylaspartate (NAA) like peak at 2.02 ppm. The same lesion was appearing hyperdense on computed tomography scan done at some other center. Midline suboccipital craniectomy was done with near-total removal of the lesion. Histopathology revealed the cyst wall comprised endothelium-lined structures of partially ciliated cuboidal to columnar cells with pseudostratification in places as well as squamous metaplasia, which was suggestive of neurenteric cyst. Immunohistochemical analysis was negative for periodic acid-Schiff stain and glial fibrillary acidic protein.\nThese space-occupying lesions (SOLs) are rare, congenital, benign, malformative endodermal lesions involving the craniospinal axis with spine being the more common location. As in our case, the majority of intracranial neurenteric (NE) cysts are located in the posterior fossa. They are classically located in the midline anterior to the brainstem and may extend to involve the cerebellopontine angle.[] While the exact source is undetermined, NE cysts possibly develop at the time of notochordal development during the phase of existence of the NE canal. The notochord and foregut are unable to split, causing primitive endodermal cells to be assimilated into the notochord. These migrant alimentary cells eventually turn into a cyst. These lesions generally measure <2 cm, and on macroscopic examination, they are smooth, thin-walled, and translucent structures. Contents of these cystic lesions vary from clear to mucoid or xanthochromic. Histopathological analysis of the cyst wall exhibits endothelium-lined structures of partially ciliated cuboidal to columnar cells. Pseudostratification may also be seen in the epithelium at random intervals and characteristically has ciliated and goblet cells. These lesions comprise only endodermal components and very much bear a resemblance to gastrointestinal tract mucosa.[]\nTypical imaging characteristics of an NE cyst comprise a circular and/or lobulated, mildly hyperintense SOL located anterior to the medulla and showing no enhancement in postcontrast images. The signal intensity of these cysts on MR sequences varies with the protein content with typical appearance of a T1 isointense to slightly hyperintense and T2-weighted/FLAIR hyperintense signal. However, in the present case, this cyst had hypointense signal on T2-weighted images which has been postulated to be due to elevated protein concentration within the cyst, squamous metaplasia, and voluminous keratinous debris. Uncommonly, these lesions may show mild restriction on DW images as well as rim enhancement in postcontrast images.[] The differential diagnosis of these cysts comprises arachnoid cyst, epidermoid cyst, Rathke and colloid cysts with the last two being other subtypes of endodermal cysts. The epidermoid has greatest similarity to the NE cyst as it is hyperintense on T1-weighted images and is often located along the midline. However, epidermoid cysts typically show restriction on DW images. On the other hand, arachnoid cysts have the same signal intensity as cerebrospinal fluid at all sequences and have no NAA peak at 2.02 ppm on MRS because of lack of neuronal elements. Rathke and colloid cysts can be distinguished from NE cysts on the basis of site.[]\nNil.\nThere are no conflicts of interest.
A 28-year-old lady presented with headache and vomiting since 11/2 years. She complained of difficulty in gripping objects with left upper limb, gait unsteadiness with tendency to sway to the left side, dysarthria and nasal regurgitation on swallowing fluids. On examination, bilateral gaze evoked downbeat nystagmus was present. Gag reflex was sluggish bilaterally but uvula was central. There was drooping of right shoulder and weakness of right sternocleidomastoid. Left cerebellar signs were present with ataxic gait. Bulk and tone of muscles was normal.\nCT [] showed a hyperdense extraxial lesion in left side posterior fossa, compressing brainstem and distorting the 4th ventricle with obstructive hydrocephalus. On MRI [], it appeared iso- to mildly hypointense on T2 weighted images and hyperintense on T1 weighted images without suppression of signal on fat saturated images. The lesion measured 5.4 × 4.2 × 5.34 cms. There was no obvious enhancement on administration of contrast. There was no restriction diffusion. On the anterior aspect of the lesion, just to the left of midline, there was a T1- and T2 hypointense focus that corresponded with slightly increased density on plain CT and showed blooming on SWI (likely calcification). The lesion showed facilitated diffusion. MRS showed a large NAA like peak at 2.02 ppm.\nShe underwent midline suboccipital craniectomy and near total excision of the lesion. Histopathology showed a cyst wall composed of pseudostratified ciliated columnar epithelium (black arrow) with extensive areas of squamous metaplasia suggestive of neuroenteric cyst.