Extra Axial Hyperdense Neurenteric Cyst at Craniocervical Junction: A Diagnostic & Surgical Challenge

Neurenteric cysts are rare congenital benign lesions of the central nervous system. These are essentially congenital endodermal cysts. Neurenteric cysts are seen more frequently in the spine than the brain (3:1), in particular involving the lower cervical/upper thoracic spine. Neurenteric cysts represent 0.31.3% of all intra spinal cystic lesions and are extremely rare intra cranially [1]. In the brain, these are more frequently seen in the infratentorial compartment rather than the supratentorial compartment (70-75%), most commonly in the prepontine region. More than 95% of these are extra-axial in location and are usually seen anterior/lateral to the pontomedullary junction, with most of them extending to the midline. While infratentorial lesions are usually less than 2cm, supratentorial lesions can often be quite large [2]. There have been a few reports of these cysts occurring in the medulla or cerebellum [3]. Since these lesions are relatively uncommon and can have variable imaging appearance, they may present as a radiological challenge and may be mistaken for other more ominous diagnoses. Attention to imaging features and location are both essential in formulating the correct diagnosis. Although these lesions can have variable T1 and T2 appearance depending on the intracystic mucinous content, a prepontine anterior/anterolateral lesion, without demonstrable contrast enhancement or diffusion restriction, should steer one towards favoring the diagnosis of a neurenteric cyst. Advanced imaging modalities such as magnetic resonance spectroscopy can serve as an additional diagnostic tool when available, as the neurenteric cysts have been shown to have N-Acetyl Aspartate (NAA)-like peak at 2.02ppm, not seen with other cystic lesions. We illustrate these teaching points via our clinical case report [4].