Regression of Chiari malformation type 2 following early postnatal meningomyelocele repair-a retrospective observation from an institutional series of patients.

Purpose: Spontaneous regression of Chiari malformation type 2 (CM2) is observed rarely, as CM2 is associated with meningomyelocele (MMC) that is surgically repaired either pre- or early postnatally. While the radiological regression of CM2 occurs frequently following prenatal repair of MMC, it has been reported in only a few studies after postnatal repair.

Methods: From the consecutive series of children with postnatally repaired MMC, we reviewed the clinical and radiological data regarding CM2, particularly its regression either spontaneously or following CSF diversion.

Results: Eighteen children underwent postnatal repair of MMC between February 2011 and April 2023. CM2 was present in 16 (89%), and hydrocephalus in 15 children (83%), requiring shunting in 14 of them. During the mean clinical observation time (from birth to April 2023) of 59 ± 51 months, three children with CM2 (19%) underwent 1-2 foramen magnum decompressions (FMD), five children (28%) 1-4 surgical untethering procedures and 13 children with shunted hydrocephalus (93%) 1-5 shunt revisions. Out of sixteen children with CM2, we observed regression of CM2 on MRI in only one case (6%) during the mean radiological follow-up (from birth to the last MRI taken) of 49 ± 51 months.

Conclusion: In our experience, spontaneous regression of CM2 in children with postnatally repaired MMC occurs quite rarely. Pathophysiological mechanisms behind the development of CM2 in children with MMC remain unclear, but our observation supports the hypothesis of an association between the downward displacement of the hindbrain and the low intraspinal pressure secondary to CSF leakage in children born with MMC.