Hemimetameric Segmental Displacement: Case Series and Review

Walter Reed Army Medical Center, Washington, DC, USA
AI duPont Hospital for Children, Wilmington, DE, USA

INTRODUCTION:
Hemimetameric segmental displacement or hemimetameric "shift", is a clinical entity defined by two contralateral hemivertebrae separated by at least one normal vertebra. Although the entity is briefly described in textbooks, there are no published series to date.

MATERIALS AND METHODS:
From 1975-2000, 186 cases of congenital scoliosis were identified at one or two referral centers. Of these, 28 cases (17 male, 11 female) of hemimetameric shift (15%) were identified. Charts and radiographs were reviewed to identify age at presentation, associated anomalies, levels/orientation of hemivertebrae, curve progression, and ultimate treatment. An MRI was obtained in all patients after 1988 (18 pts.).

RESULTS:
Average age at presentation was 4.8 years (range, 1 day-27 years) with an average follow-up of 5.6 years (range 9 months to 14 years). Hemivertebrae averaged 2.9/pt. (range 2-6) with the following distribution: T1-T6 (20), T7-T11 (29), T12-L1 (8), L2-L4 (12), and L5 (3). All patients were followed for curve progression with ten patients undergoing bracing (surgeon dependent). Eleven patients required surgery to prevent further curve progression - most commonly with involvement of the thoracolumbar or lumbosacral junction. Eleven patients also had associated anomalies: Klippel-Feil syndrome (3), Goldenhar's syndrome (2), imperforate anus (2), tracheo-espophageal fistula (2), single kidney (2). There was only one abnormal MRI (5.6%) - hydromyelia at T11 with a lipoma at filum terminale. There were no abnormalities noted on physical examination, however, one patient had urinary incontinence (same patient with the abnormal MRI).

CONCLUSIONS:
Hemimetameric shift is a common finding in congenital scoliosis. Hemivertebrae are most commonly found in the thoracic spine, however, surgical intervention to prevent further curve progression is most common with involvement of the thoracolumbar or lumbosacral junction. Interestingly, the incidence of abnormal MRI findings is quite low (5.6%).