Perinatology and Pathology Unit, Carabobo University, Valencia - Venezuela

Definition: Neurenteric cysts are the combination of an endodermal cyst with a vertebral dysplasia that is located in the posterior mediastinum, preferentially on the right side, which presumably arise from misplaced epithelium of nasopharynx, respiratory tree or intestinal tract. The most common form consists of a simple epithelium resting on a delicate fibrovascular capsule. It may be unilocular or septated and have different types of epithelium (ciliated or non ciliated, columnar, intestinal glands, pancreatic and salivary glands tissues) and a muscular wall with smooth mucosal lining.

Incidence: Rare, male predominance. First case reported in 1934 by Pussep.

Synonyms: Enteric, endodermal, enterogenous, epithelial-line or teratomatous cyst.

Localization: Neurenteric cyst are usually located in the posterior mediastinum, but can be intracranial and throughout the length of the spine, in particular in the lower cervical and upper thoracic regions with intradural, extramedullary location. They may also establish connections with parts of the gastrointestinal tract[1].

Pathogenesis: Neurenteric cysts are frequently associated with vertebral abnormalities including hemivertebrae and spina bifida. Lower cervical and upper thoracic vertebrae are usually affected. Different theories have postulated that the developing foregut adheres focally to the notochord with further development of a traction diverticulum that results in a foregut cyst and associated vertebral anomaly. Another theory is that the gut herniates into a gap formed by a split notochord. A persistent neurenteric canal has been postulated. The cyst in the posterior mediastinum is frequently attached to the vertebra by a fibrous band and may extend intraspinally through a spinal defect (hemivertebra and anterior spina bifida). In a third of the patients these cyst are associated with malformations of CNS and/ or GI tract.

Embryology: Neurenteric cyst represent a failure of complete separation of the notochord from the foregut during the 3^rd week of embryogenesis.

Diagnosis: A well-defined intrathoracic tubular or round cystic image, with vertebral connection through a hole in one vertebra. The cyst can cause cardiac malposition and hydrops. Polyhydramnios can be present[2],[3],[4].

Case report: 20 years old G1P0 woman, referred at 35 weeks of pregnancy for evaluation of a fetal thoracic lesion. The cystic mass in the chest has the following characteristics:

• the fluid is clear, and the low-level echoes that are seen on the posterior aspect have more the appearance of side-lobe artifacts then "debris".

• although this is a large cyst that is partially in several regions of the chest, the most important region for the differential diagnosis is that the cyst occupies the posterior mediastinum. If the cyst had been in the right lateral region, a pulmonary origin would have been almost the only likely differential diagnosis. Arising from the posterior mediastinum enlarges the diagnosis considerably.

• it displaces the heart.

Thoracic spine and posterior fossa demonstrated some irregularity of the thoracic spine.

The head (normal Doppler), was large (note the spacing of the dots along side the Doppler window, compared to the spacing of the dots on the image of the heart above). More important there was some soft-tissues edema at the level of the skull.

Evolution

The baby was born at 37 weeks weighing 3250g with an APGAR score of 2 points at the first minute and O points at 5 minutes. He died of an acute respiratory failure due to lung hypoplasia. The enlargement of the head is well visible. No hydrocephaly though.

The pathology confirmed the diagnosis of neurenteric cyst of the posterior mediastinum (endodermic cyst).

The communication between the cyst and the central nervous system could be demonstrated by increasing the intracranial pression and demonstrating the increased turgescence of the cyst.

Section of the spine exquisitely demonstrated the communication. Note the opening in the vertebral body and the sac surrounding the spinal cord. There was also a hemivertebra.  

At microscopy, the cyst had a wall lined by intestinal mucosa composed of different types of epithelia: cylindrical ciliated, planar stratified, small intestine glands and colonic glands. There were no cellular atypias.

Differential diagnosis: Bronchogenic cysts, herniated stomach (diaphragmatic hernia, hiatal hernia), gastrointestinal duplication cysts, pericardial, mesothelial, thoracic duct and parathyroid cysts, anterior meningocele, cystic adenomatoid malformation of the lung type 1 (macrocystic), pleuropulmonary blastoma (Type I)[5] and intrathoracic solitary cyst of the liver[6]

Associated anomalies: Include vertebral anomalies, abnormal gastrointestinal connections, and esophageal atresia[7].

Macroscopic findings: Unilocular or septated thin-walled sacs filled with clear, gray-white, yellow or green viscous or mucoid material, located in the posterior mediastinum close to the esophagus, typically in a retrocardiac position.

Microscopic findings: The most common form of endodermal cyst consists of a simple epithelium resting on a delicate fibrovascular capsule. Microscopically a thick smooth muscle wall with two or three layers is characteristic. Columnar (native state) or low cuboidal epithelium (due to chronic pressure) is evident. Ciliation is a variable feature but many cells contain globules of mucus. Duodenal glands may be present and pancreatic and salivary gland tissues have been described. Enteric cysts have been classified into three groups, according to histological features.

• Group A is the simplest type, lined by a single layer of cuboidal or columnar epithelial cells with or without cilia.
• Group B cysts include more complex elements of the gastrointestinal tract or tracheobronchial tree, including mucus glands and smooth muscle in their wall.
• Group C cysts have ependymal or glial tissue in addition to the elements seen in group B cysts.

Most neurenteric cysts belong to group A. Squamous metaplasia is occasionally encountered.

Treatment: There are reports of intrauterine treatment by thoracentesis or placement of a thoracoamniotic shunt if the cyst appears to cause lung hypoplasia.

Postnatal evolution: Symptoms of respiratory distress become obvious at birth or during the first months of life, neurological symptoms can develop later. The therapy of choice is complete resection of the cyst.[8],[9]

References:

Mackenzie IRA, Gilbert JJ. Cysts of the neuraxis of endodermal origin. J Neurol Neurosurg Psych 1991;54:572-5

Bremar JL. Dorsal intestinal fistula: accessory neuroenteric canal; diastematomyelia. Arch Pathol 1952;54:132-8.

McLetchie NGB, Purves KJ, Saunders RL de Ch. The genesis of gastric and certain intestinal diverticula and enterogenous cyst. Surg Gynecol Obstet 1954;99:135-41.

Prop N, Frensdorf EL, Van De Stadt FR. A postvertebral endodermal cyst associated with axial deformities; a case showing the "endodermal-ectodermal adhesion syndromeâ€. Paediatrics1967;39:555-62.

Ellis AM, Taylor TK. Intravertebral spinal neurenteric cysts: a unique radiographic sign--"the hole-in-one vertebra". J Pediatr Orthop 1997 Nov-Dec;17(6):766-8