CASE 18608 Published on 10.07.2024

Foetal MRI in the prenatal diagnosis of terminal myelocystocele


Paediatric radiology

Case Type

Clinical Case


Leire Ormaetxe Albeniz, Patricia Rodríguez Ripalda, Lander Antón Méndez, Juan José Gómez Muga, Itziar Aza Martínez

Department of Radiology, Basurto University Hospital, Bilbao, Spain


foetus, 34+4 weeks pregnancy

Area of Interest Paediatric ; Imaging Technique MR
Clinical History

34-year-old primigravida, 34+4 weeks pregnant, previously healthy. A routine foetal ultrasound revealed a cystic sacral lesion. Subsequently, a sequential foetal MRI was performed.

Imaging Findings

Foetal MRI showed an 11 cm wide cystic mass, isointense to cerebrospinal fluid (CSF), arising through a midline dorsal sacral defect, formed by two non-communicated compartments, divided by a laminar septation. The proximal component communicated with the ependimary sac and showed internal lineal septations extending from an abnormally descended medullar cone to the wall of the cyst, suggesting a tethered cord syndrome. The second larger compartment, located surrounding the first one giving the lesion a cyst-within-a-cyst appearance, showed a thinner wall and a subtle skin cover. No spinal vertebrae were identified distally to the lesion’s origin, suggesting an associated partial sacral agenesis (Figures 1a, 1b and 1c). No intracranial abnormalities or Chiari malformations were identified (Figure 2).

The meconial intestinal content showed a normal signal intensity on T1- and T2-weighted images, excluding the presence of associated anorectal malformations. However, the abdominal study revealed a left kidney agenesia (Figures 3a and 3b). At birth, the existence of a sacral skin-covered lesion was confirmed (Figure 4).



Neural tube defects are a complex group of congenital pathologies resulting from the incomplete closure of the neural tube. They can affect any level of the central nervous system, leading to cranial defects or spinal dysraphisms (SD), with predominant involvement of the lumbosacral region.

Antenatal diagnosis is important to ensure early treatment, rule out associated malformations and minimize long-term sequelae.

Clinical Perspective

As most of these lesions manifest as lumbar masses with variable neurological deficits, the clinical distinction may be complicated. This underscores the role of prenatal imaging.

Imaging Perspective

The first step in the differential diagnosis requires classifying the SD into two groups based on the presence of mesenchymal elements covering the spinal cord, distinguishing open and closed forms. Closed SD are further subdivided into two additional groups, depending on the presence or absence of a subcutaneous mass. Meningoceles, terminal myelocystoceles and lipoma-associated dural defects belong to the first group [1].

Myelocystoceles constitute a rare form of SD resulting from a defect in secondary neurulation. They are characterised by the herniation of a hydrosyringomyelic cavity through a spinal dorsal defect into a meningocele, typically affecting the terminal spine.

The terminal hydrosyringomyelic cavity forms as an extension of a dilated ependymal canal, while the surrounding meningocele arises from enlargement and herniation of the subarachnoid space. Therefore, the CSF of the syringomyelia does not communicate with the CSF within the meningocele, conforming a bicompartmental lesion covered by mesenchymal tissue [2].

The main differential diagnosis is established with myelomeningoceles, the most common form of open SD. In this pathology, it may also be possible to identify the spinal cord entering a meningocele and anchoring to the placode, but its defining feature is the direct environmental exposure [2,3].


Although spinal dysraphisms may occur sporadically, their diagnosis necessitates ruling out associated malformations, including the OEIS complex (omphalocele, bladder exstrophy, imperforate anus and sacral agenesis) and Currarino syndrome (anorectal malformation, sacrococcygeal osseous defect and presacral mass).

Signal abnormalities within the intestinal content (physiologically T2-hypointense and T1-hyperintense in the colon and opposite for the small bowel) can serve as indirect indicators of anorectal malformations with fistulisation.

In this particular case, left renal agenesia was identified. Surgical and histological findings confirmed the diagnosis of terminal myelocystocele.

Learning Points

  1. SD encompass a complex group of congenital pathologies with a significant risk of long-term sequelae, requiring early diagnosis.
  2. Distinguishing between open and closed dysraphisms and assessing for potential associated subcutaneous masses are crucial steps in narrowing down the differential diagnosis.
  3. Terminal myelocystoceles represent a rare form of closed SD characterised by the herniation of a hydrosyringomyelic through a posterior sacral defect into a meningocele, acquiring a cyst-within-a-cyst appearance.

All patient data have been completely anonymised throughout the entire manuscript and related files.

Differential Diagnosis List
Terminal myelocystocele
Currarino syndrome
OEIS complex
Final Diagnosis
Terminal myelocystocele
Case information
DOI: 10.35100/eurorad/case.18608
ISSN: 1563-4086