Three-dimensional analysis of volumetric changes in herniated discs of the lumbar spine: does spontaneous resorption of herniated discs always occur?

Purpose To investigate volumetric changes in lumbar disc herniation (LDH) using three-dimensional measurements obtained by magnetic resonance imaging (MRI) and to identify possible factors affecting such changes. Methods Between January 2004 and December 2011, 43 patients who underwent conservative treatment for LDH were enrolled. In all, 56 disc levels were investigated. MRI was performed on two or more occasions (minimally, at the initial visit and 6 months later). The volume of each herniated disc was determined. For each patient, disc migration, morphology, initial LDH size, and clinical outcome were evaluated. Results The mean volumes of herniated discs at the initial and follow-up visits were 1,304.57 +/- 837.99 and 993.84 +/- 610.04 mm(3), respectively. The mean change in volume from the initial to the follow-up visit was 310.73 +/- 743.60 mm(3). Volumes decreased at 35 disc levels and increased at 21 levels. The disc containment, the extent of LDH, the initial size of the herniated disc, and the degree of intactness of the posterior longitudinal ligament were significantly correlated with disc resorption and an increase in disc volume (p = 0.01, p = 0.018, p = 0.001, and p < 0.001, respectively). No significant association was evident between disc volumetric change and clinical outcome. Conclusions We observed that LDH is a dynamic disease and that a herniated disc is not always spontaneously resorbed, in contrast to what has been reported previously. Alleviation of clinical symptoms can be achieved via conservative treatment even if the volume of the herniated disc changes. Spinal surgeons should not only present an option of initial non-surgical treatment to LDH patients but should also inform them that the LDH may change in size during daily activity or exercise.