Dural Ectasia (DE) and Plain Radiography in the Marfan Lumbosacral Spine

Johns Hopkins Department of Orthopaedic Surgery
Baltimore, Maryland, USA

INTRODUCTION:
Dural ectasia (DE) is a ballooning or expansion of the dural sac commonly seen in the lumbosacral spine of patients with Marfan syndrome. It has been shown that DE in Marfan is associated with severe low back pain and headaches, and neurologic deficits such as weakness and loss of bowel and bladder function. For these reasons, increased attention has been directed towards screening for DE in this population. MRI is the gold standard for detecting DE in Marfan with a sensitivity and specificity over 90%; CT has values over 80%. However, these tests are costly, and MRI is often unavailable because of prosthetic heart valves for associated cardiac disease. Plain radiographs are an inexpensive and simple means of evaluating the lumbar spine. The purpose of this study was to determine if plain radiography can accurately detect DE in Marfan. This is the only study in the literature examining the utility of plain x-rays in making this diagnosis.

MATERIALS AND METHODS:
Fifty patients with Marfan syndrome as defined by the Ghent criteria aged 30-50 participated in this study. The study population included 25 Marfan patients with DE and 25 age- and sex-matched Marfan patients without DE. Plain films of the lumbosacral spine were taken and five measurements were made at each level from L1-S1: interpediculate distance (IPD), scalloping value (SV), sagittal canal diameter (SCD), vertebral body width, and transverse process width. Pre-existing MRI scans were available in all patients and used as gold standards for the presence or absence of DE.

RESULTS:
The measurements most significantly associated with DE were: IPD at the L4; SV at L5; SCD at S1. Criteria were developed based on these values using an analysis of variance to generate "critical values" for each measurement. These final criteria included the presence of one of the following: IPD at L4 > 38.0 mm; SCD at S1 > 18.0 mm; or SV at L5 > 5.5 mm. Using these criteria against the gold standard MRI scans, plain radiography was found to detect DE in Marfan with a very high specificity (92%) but a lower sensitivity (76%).

CONCLUSION:
Dural ectasia in Marfan syndrome is commonly associated with several osseous changes that are observable on conventional radiographs of the lumbosacral spine. Conventional radiography can detect DE in patients with Marfan syndrome with a very high specificity and a reasonably high sensitivity. Thus, if the criteria are met on plain radiographs, one should have a high index of suspicion that DE is present. Consideration should therefore be given to using plain radiography as a screening tool in Marfan patients with symptoms consistent with DE.