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Neurenteric Cyst / Diastematomyelia

Findings:

The case on the top demonstrates a septated intrathoracic cyst associated with abnormal, butterfly vertebrae in the lower cervical region. The case on the bottom demonstrates an intraspinal bony spur (arrow) separating the neural elements.

Discussion:

The case on the on the top demonstrates an intrathoracic cyst associated with vertebral abnormalities. This constellation of findings could only be the result of a neurenteric cyst. While a neurenteric cyst is often considered in the differential diagnosis of cystic fetal intrathoracic masses, it is poorly understood. It has only been in the past 40 years that clinicians have gained a better understanding of the association of developmental anomalies of the skin of the back, the spine, the central nervous system and the intestines. While there are a number of theories as to the etiology of entities such as neurenteric cysts, the most widely accepted explanation is the "split notochord syndrome". Over one hundred years ago it was shown experimentally that clefts could be produced in fish and frog embryos with dorsal protrusion of the yolk sac into the amniotic cavity. In the 1900's Bremer et al and Saunders et al showed that this phenomenon could be demonstrated in humans. In the 1960's Drs. Bentley and Smith reviewed the embryology of this developmental abnormality, from which much of the following discussion is taken. An embryo may develop with partial duplication and separation of the notochord, the level and extent being variable. Through this separation or gap the ventrally situated yolk sac or gut 'anlage' endoderm will herniate and eventually adhere to the dorsal ectoderm or skin anlage. The hernia may rupture to produce a fistula from the yolk sac into the amniotic cavity which separates the halves of the future spinal cord and spinal column. Subsequent differential growth of the embryo tends to close and obliterate the fistula. This process may affect the development of the base of the skull, vertebral column, and central nervous system. Persisting remnants of the yolk sac origin may differentiate into tissues characteristic of any part of the gut or its embryological derivatives such as the lung, etc. Differential rates of growth of the gut and vertebral column leads to a wide separation of the areas within the abdomen passing through these abnormal openings in the diaphragm to a high vertebral attachment. In addition, abnormal fixation of the gut to the vertebral column may cause subsequent failure of normal intestinal rotation.

These abnormalities may be classified into two major categories: a) visceral malformations and b) spinal and central nervous malformations. Visceral malformations are often classified as enteric remnants. These may comprise certain diverticula or cysts connected by fibrous strands to the anterior aspect of the body of a vertebra situated cephalad to the enteric remnant. The affected vertebral body is often bifid, and a complete anterior and posterior spina bifida occasionally exists. Histologically, examination of the remnant will usually show the presence of smooth muscle and enteric mucosa in the walls of the lesion. The mucosal type may differ from that of the gut to which it lies adjacent, and it may be flattened and atrophic, the appearance giving no clue to its derivation. The developmental posterior enteric remnants considered under the heading of visceral malformations may be subdivided as follows:

Posterior Enteric Remnants

Fistulae

When obliteration of the embryonic fistula fails completely the track passes backgut through the mesentery or mediastinum, traverses a complete spina bifida which may be coupled with a diastematomyelia, to open on the skin in the midline of the back.

Sinuses

The dorsal part of the embryonic fistula is all that persists. It forms a sinus derived from cutaneous or enteric tissues that passes forward from the midline of the skin of the back. There may be an underlying posterior or complete spina bifida.

Posterior Enteric Diverticula

The ventral part of the embryonic fistula remains and communicates with the gut. There may be an associated anterior spina bifida or fibrous adhesion to a vertebral body.

Posterior Enteric Cysts

Only an intermediate part of the embryonic fistula or diverticulum persists and the atrophic portions are represented by fibrous bands. These cysts may be prevertebral (posterior mediastinal or mesenteric), vertebral (spinal or mid-brain) or postvertebral in position. These processes are not enteric duplications which should be restricted to anomalies attributable to defects of embryonic vacuolation of the gut.

From: Bentley JFR, Smith JR. Developmental posterior enteric remnants and spinal malformations: The split notochord syndrome. Archives Dis Childhood 35:76-86, 1960

Spinal and Central Nervous Malformations -

When the opening in the dorsal tissue mass of the split notochord closes incompletely the resultant spinal defect may range from a slight widening of the vertebrae to a complete anterior and posterior spina bifida. Minor degrees of anterior spina bifida produce the radiological appearance known as butterfly vertebrae. Fusion of the medial pedicles results in the bony spur found in diastematomyelia. Likewise, fusion of the cervical vertebrae constitutes the osseous element in the Klippel-Feil syndrome, and these vertebral bodies are often split. The spinal canal is widened in each of these types of vertebral abnormalities and anterior meningoceles may protrude where the spine is bifid. When the spinal cord is itself cleft, the separated halves seldom rejoin inferiorly, possibly due to tethering by the nerve roots.

Diastematomyelia

From: Bentley JFR, Smith JR. Developmental posterior enteric remnants and spinal malformations: The split notochord syndrome. Archives Dis Childhood 35:76-86, 1960

Differential Diagnosis

A number of intrathoracic masses may simulate a neurenteric cyst including cystic adenomatoid malformation, congenital diaphragmatic hernia, bronchogenic cyst and teratomas. Certainly the most similarly appearing lesion is that of a cystic adenomatoid malformation of the lung. The presence of vertebral abnormalities and the absence of adjacent lung hyperechogenicity make this possibility less likely.

Type I macrocystic cystic adenomatoid malformation

References:

Bentley JFR, Smith JR. Developmental posterior enteric remnants and spinal malformations: The split notochord syndrome. Archives Dis Childhood 35:76-86, 1960

Smith JR. Accessory enteric formations: A classification and nomenclature Archives Dis Childhood 35:87-89, 1960

Macaulay KE, Winter III TC, Shields LE Neurenteric cyst shown by prenatal sonography. Amer J Roentgenol 169:563-565, 1997

Rizalar R, Demirbilek S, Bernay F, Gurses N A case of mediastinal neurenteric cyst demonstrated by prenatal ultrasound. Eur J Pediatr Surg 5:177-9, 1995

Fernandes E, Custer M, Burton E et al. Neurenteric cyst: surgery and diagnostic imaging. J Pediatric Surgery 26:108-110, 1991

 

 

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California