Clinical outcomes and bony restenosis after foramen magnum decompression for achondroplasia patients.

PURPOSE: Achondroplasia is a genetic syndrome characterized by short stature and rhizomelic shortening of the limbs. Many patients also exhibit craniocervical junction stenosis, which often progresses to spinal cord compression or hydrocephalus. Foramen magnum decompression (FMD) is performed to relieve stenosis at the craniovertebral junction. The purpose of this study was to analyze the clinical outcomes of FMD in achondroplasia patients and to discuss restenosis due to bone regrowth (bony restenosis), an important cause of postoperative worsening. METHODS: Medical records and brain imaging data of 89 pediatric achondroplasia patients who visited our institution between January 2012 and April 2022 were retrospectively analyzed. RESULTS: Among 89 achondroplasia patients, FMD was performed in 38 patients. During the median 60 months of follow-up after FMD, eleven patients developed warning changes at MRI. Warning changes consisted of four types: restenosis due to bone regrowth (bony restenosis), restenosis due to soft tissue thickening, de novo T2 HSI of the cervical spinal cord, and progression of ventriculomegaly. Patients with bony restenosis (3 of 38; 7.9%) required reoperation of FMD. The age of restenosis was 46, 48, and 98 months old, and the time interval after FMD was 38, 34, and 87 months, respectively. Removal of bony spur was performed and no recurrence of bony restenosis was found until the most recent follow-up. CONCLUSION: Bony restenosis was observed in 3 of 38 patients (7.9%) after FMD during the follow-up. Regular imaging studies and close observation until late childhood may be reasonable for early detection and management of bony restenosis.