Early adjacent-level vertebral osteonecrosis within the Kümmell spectrum after L2 kyphoplasty: CT-demonstrated intravertebral vacuum cleft with low STIR signal

Kümmell disease has traditionally been defined as delayed post-traumatic vertebral collapse following a symptom-free interval. Contemporary understanding, however, broadens this entity into a spectrum of post-fracture vertebral osteonecrosis, nonunion, and dynamic pseudarthrosis. The intravertebral vacuum cleft (IVC) is a key imaging hallmark of this condition, but its magnetic resonance imaging (MRI) appearance is not uniform: fluid-predominant clefts typically show hyperintensity on fluid-sensitive sequences, whereas gas-predominant clefts may present as low signal or signal void. This variability poses a diagnostic pitfall, as reliance on MRI alone can be misleading in cases where gas dominates the cleft content. An 89-year-old woman with severe osteoporosis underwent L2 kyphoplasty for an osteoporotic compression fracture. Preoperative imaging (CT and MRI) confirmed an intact L1 vertebra with no fracture signal. Approximately 10 days postoperatively, she developed recurrent low-back pain exacerbated by positional changes. Follow-up radiographs revealed rapid L1 collapse. Subsequent MRI showed a low-signal intravertebral band on fat-suppressed T2/STIR sequences, lacking the diffuse marrow edema typically expected in an acute fracture. CT then conclusively demonstrated a transverse gas-density intravertebral vacuum cleft within the collapsed L1 body, while bone scintigraphy showed no significant uptake at L1. Based on the temporal sequence, positional pain, rapid collapse, and CT evidence of a vacuum cleft, the lesion was diagnosed as early adjacent-level Kümmell disease—vertebral osteonecrosis within the Kümmell spectrum. L1 kyphoplasty effectively relieved her symptoms. This case highlights an atypical but pathophysiologically coherent form of Kümmell disease in which the cleft was gas-dominant and therefore low signal on STIR rather than hyperintense. The diagnostic lesson is that CT should be obtained promptly when MRI is inconclusive, because gas-dominant clefts may be occult on fluid-sensitive sequences. The combination of both modalities provides the most reliable diagnosis, rather than relying on either alone.