Medullary Tegmental Cap Dysplasia: Fetal and Postnatal Presentations of a Unique Brainstem Malformation

Abstract

Background and purpose: Medullary tegmental cap dysplasia is a rare brainstem malformation, first described and defined by James Barkovich in his book Pediatric Neuroimaging from 2005 as an anomalous mass protruding from the posterior medullary surface. We describe the neuroimaging, clinical, postmortem, and genetic findings defining this unique malformation.

Materials and methods: This is a multicenter, international, retrospective study. We assessed the patients' medical records, prenatal ultrasounds, MR images, genetic findings, and postmortem results. We reviewed the medical literature for all studies depicting medullary malformations and evaluated cases in which a dorsal medullary protuberance was described.

Results: We collected 13 patients: 3 fetuses and 10 children. The medullary caps had multiple characteristics. Associated brain findings were a rotated position of the medulla, a small and flat pons, cerebellar anomalies, a molar tooth sign, and agenesis of the corpus callosum. Systemic findings included the following: polydactyly, hallux valgus, large ears, and coarse facies. Postmortem analysis in 3 patients revealed that the cap contained either neurons or white matter tracts. We found 8 publications describing a dorsal medullary protuberance in 27 patients. The syndromic diagnosis was Joubert-Boltshauser syndrome in 11 and fibrodysplasia ossificans progressiva in 14 patients.

Conclusions: This is the first study to describe a series of 13 patients with medullary tegmental cap dysplasia. The cap has different shapes: distinct in Joubert-Boltshauser syndrome and fibrodysplasia ossificans progressive. Due to the variations in the clinical, imaging, and postmortem findings, we conclude that there are multiple etiologies and pathophysiology. We suggest that in some patients, the pathophysiology might be abnormal axonal guidance.

FIG 1.

Illustration of the medullary cap morphologic characteristics: A, Smooth; B, Stick sign; C, Globular; D, Step sign; E, Caterpillar sign.

FIG 2.

MR imaging and ultrasound showing the medullary cap in 12 patients, midsagittal view. A, Patient 1; B, Patient 2; C, Patient 3; D, Patient 4; E, Patient 5; F, Patient 6; G, Patient 7; H, Patient 8; I, Patient 9; J, Patient 11; K, Patient 12; L, Patient 13. Of note, patient 10’s MR imaging is separately shown in the Online Supplemental Data.

FIG 3.

A, Axial microscopy photograph of the medulla oblongata of patient 2 at 35 gestational weeks. The right-posterior bulge of the medulla oblongata (RMO) contains many mature neurons, consistent with a hamartoma, connected to the cerebellum. The inferior olivary nuclei (ON) are well-developed, and the pyramidal tracts (PT) are intact. B, Postmortem photograph of patient 3 depicts the fetal posterior fossa after removal of the occipital bone, performed at 17 gestational weeks. Note the thickening and internal rotation of the RMO, producing the medullary cap shape. Cbl indicates cerebellum; FM, opening of the foramen of Magendi.