CNS NE cysts are uncommon congenital cysts most commonly encountered in the spinal cord as intradural extramedullary cysts. They are generally, situated ventral to the spinal cord and are most commonly seen in the lower cervical and upper thoracic regions. These cysts are believed to originate from the endoderm during early embryonic life.[1
] Several theories have been proposed to explain the pathogenesis of neurenteric cysts. Failure of separation between the notochord and the foregut that leads to incorporation of primitive endodermal cells in the notochord was proposed. However, this mechanism does not explain the existence of supratentorial cysts as the most rostral extent of the endoderm is at the level of the clivus.[3
] The “Seessel's pouch origin” hypothesis suggest a common origin for suprasellar neurenteric cysts, Rathke's cleft cysts and colloid cysts. This theory fails to explain the laterally positioned supratentorial cyst. On the other hand, Mittal et al
. propose that anomalous endodermal cell migration occurs dorsally through the primitive neurenteric canal into the ectoderm and can travel cephalad and to more lateral positions. This progress explains the decreasing incidence of NE cysts from the spine toward the infra and supratentorial compartments, respectively.[2
] Given the endodermal origin of NE cysts, elements of bronchial or gastrointestinal epithelium may be seen in these cystic lesions. Furthermore, NE cysts can also contain elements derived from mesoderm and ectoderm.[2
] This complex histopathology lead to the use of several names that can be interchangeably used with NE cysts including endodermal, enteric, enterogenous, respiratory, gastroenterogenous and archenteric cysts and have also been labeled as gastrocytomas or intestinomas.[2
In our review of literature, using the keywords, NE, enterogenous, endodermal and supratentorial cysts, we identified around 30 reported cases . The male to female ratio is 1.3:1 with age range between prenatal and 78 years. Clinically, supratentorial NE cysts present with symptoms of space occupying lesion depending on their location such as headache, visual changes, insomnia, seizures, mental and personality changes.
Summary of previous case reports describing supratentorial neurenteric cysts
Supratentorial NE cysts are reported to be larger in size than those in the posterior fossa. Supratentorial locations include supra or parasellar,[9
] septum pellucidum,[25
] third ventricle,[7
] anterior fossa[4
] and along the optic nerve.[6
] The majority of supratentorial NE cysts occur in extra axial location with no definite laterality predilection. However, there are few reports of intraparenchymal NE cysts in the frontal[3
] and temporal lobes.[21
] All the previously reported and pathologically proven cases of supratentorial NE cysts are solitary. Walls et al
. reported a case of multiple intracranial enterogenous cysts in which they presumed that the supratentorial intraparenchymal cysts are of similar pathology to the infratentorial cystic lesions.[5
] In general, NE cysts are well-defined, smooth and thin-walled, round or lobulated and rarely demonstrate marginal calcifications.
The signal characteristics of NE cysts vary depending on the protein content of the cysts. The majority of NE cysts is proteinaceous and exhibit iso to increased T1-weighted signal compared with the CSF. On T2W sequence, most of the cysts show increased signal and the remaining are hypointense. On the other hand, NE cysts can be hyperintense on FLAIR images and may show mildly impeded diffusion. Although rim of enhancement is rarely seen, Preece et al
. described this finding in approximately 35% with no definitive correlation between chronic inflammatory changes/cyst rupture and rim enhancement.[1
Complete surgical excision of supratentorial NE cysts is considered the treatment of choice. This has been achieved in most of the reported cases as the cyst could be easily dissected form the surrounding meninges and brain parenchyma. Incomplete resection or cyst fenestration may result in cyst recurrence[22
] or seeding of the cyst contents into the arachnoid space.[27
Histologically, NE cysts are classified by Wilkins and Odom's into three categories.[28
] All types share the presence of single layer of pseudostratified columnar or cuboidal cells mimicking respiratory or gastrointestinal epithelium. Type B exhibits complex invaginations with glandular organization; mucinous or serous production; nerve ganglion, lymphoid, skeletal muscle, smooth muscle, fat, cartilage and/or bone elements. Cysts with ependymal or glial tissue are classified as Type C.[22
The coexistence of supratentorial NE cyst and intraparenchymal subependymoma has been described.[22
] Mucinous low-grade adenocarcinoma was reported to arise from an infratentorial NE cyst.[29
] Furthermore, malignant transformation was seen in supratentorial NE cysts into invasive mucinous papillary cystadenocarcinoma[19
] and well-differentiated papillary adenocarcinoma.[8
In contrast to NE cysts, intracranial hydatid cysts are rare acquired cystic lesions secondary to Echinococcus granulosus infection encountered in 2% of cases.[30
] The most common location of CNS hydatid cysts is in the parenchymal territory of the middle cerebral artery and less commonly in the subarachnoid space.[31
] The lesions are usually well-defined, spherical, thin and smooth-walled with no peripheral calcifications or enhancement. The cyst contents follow the appearance of CSF on both MR and CT. MRI, particularly T2W, can be better in depicting the wall due to the increased contrast between the cyst contents and the hypointense wall. Hydatid cysts are rarely multiple secondary to hematogenous spread or when complicated by traumatic or intraoperative rupture.
Although some intracranial cystic lesions may have distinct imaging features, the differentiation between NE cysts, hydatid cysts and other benign and malignant cystic lesions can be difficult on imaging due to the similarity in imaging features. In our case, the presence of debris within the cyst, the location and appearance of the lesion as well as the presence of mesenteric cyst initially suggested the diagnosis of hydatid cyst, which was the presumed pre-operative diagnosis. This case illustrates the similarity of imaging features between hydatid and supratentorial NE cysts that require a different management approach.