Hypertrophy of ligamentum flavum mimicking lumbar disc herniation.
Abstract
The most common cause of a spinal root compression is intervertebral disc herniation. Although there are patients with clinical and radiological findings of disc herniation, no disc pathology is found at operation. We present the case of a 38-year old man who was admitted in our clinic because of right fifth lumbar (L5) nerve root compression symptoms. Magnetic resonance imaging (MRI) of the lumbar spine revealed a lumbar disc herniation at the four-fifth intervertebral lumbar level (L4-L5). During operation a fold of the ligamentum flavum was found to compress nerve root, which was excised. After the operation the patient had fully recovered. We describe herein this case in order to denote that an image on MRI studies of disc herniation may represent a fold of ligamentum flavum. Thin slices MRI studies of the affected area may be could scrutinize the imaging misdiagnosis.
Case presentation
A 38-year-old man, a worker in building companies, was admitted in our clinic because of low back pain with radiation to the right leg, which was lasting for about two months before his admission, followed by leg weakness. The patient in the physical examination showed only limitation of straight leg raising test on the affected side. The symptoms were these of L5 nerve root involvement. The patient related the onset of his symptoms to a specific episode of trauma caused by lifting of a heavy object. The initial symptom was hip pain.
Lumbar MRI revealed L4-L5 intervertebral disc herniation (Figure 1, 2). Plain x-rays and myelography were not performed.
Fig.1:Axial T2 MRI image showing disc herniation
Fig 2: Sagittal T2 MRI image depicting disc herniation. Attention should be paid in the different coloration of disc and lesion
During the operation hypertrophic ligamentum flavum was found and excised. Further exploration of the intervertebral disc space and the neighbouring lumbar spinal canal revealed no disc herniation, fragmentation or sequestration. Postoperatively the patient was markedly improved.
Discussion
Although intervertebral disc herniation accounts mostly for a cause of low back pain and sciatica it is nowadays generally accepted that posterior structures play also an important role in this pathology1. In cases of posterior spinal elements symptomatology the pain is referred pain originating from the posterior ramous of the spinal nerve.
Various explanations have been proposed to account for radicular symptoms in the absence of a protruded disc. Most explanations have blamed structures which might narrow the nerve root foramen such as thickened ligamentum flavum2,3, subluxation of the facet joints4,5, retropulsion of one vertebral body on its neighbouring6, adhesions between the nerve root and the posterior ligaments7, general bulging of the whole edge of the disc8 and protrusion of the posterior longitudinal ligament 9.
In the literature there are a few reports concerning ligamentum flavum hypertrophy simulating lumbar disc protrusion10,11. It was shown that degeneration of lumbar ligamentum flavum can cause lumbar stenosis and root pain and that resection of it can relieve the symptoms11.
Fibrosis is believed to be the main cause of ligamentum flavum hypertrophy, which is caused by the accumulation of mechanical stress, with or without the aging process, especially along the dorsal aspect of the ligamentum flavum12,13. Our patient was a worker in house building companies and heavy mechanical stress was an everyday situation for him.
MR images in the sagittal plane are important in demonstrating hypertrophy of the ligamentum flavum and can provide accurate measurements of its thickness14. In our case it was not easy to recognise from MR images hypertrophy of the ligamentum flavum. May be acquisition of thin slices MR images of the affected area could pose the diagnosis in such a case.