Imaging diagnosis
Case 220
【Progress】
He was transported to the university hospital where intensive orthopedic surgery enabled to be done including extradural drainage.
【Discussion】
There are three main muscles surrounding lumbar spine from anterior to posterior: psoas muscle, quadratus lumborum muscle and paralumbar muscle. Paralumbar muscles contain multifidus muscle and erector lumbar muscle. At the level of intervertebral foramen, psoas muscle and paralumbar muscle are more adjacent to intervertebral foramen than quadrant muscle. Then, when epidural abscess occurs, it can more spread to psoas muscle and paralumbar muscles than quadratus lumbar muscle. In our case, three abscesses of epidural space, psoas muscle and paralumbar muscle were found simultaneously.
When infection occurs in vertebra or disk, it can spread easily to anterior to vertebra, namely psoas muscle and hardly to posterior to vertebra, including paravertebral muscle simply because vertebra and disk situate anterior part of spine (1-5). But when infection occurs in epidural space, it can spread not only to anterior part but also to posterior part, namely paralumbar muscle including erector lumbar muscle and multifidus muscle. Then, in our case, it is possible that the origin abscess arises from epidural abscess but not from vertebra and disk since there was no abnormal findings on vertebra and disk.
Epidural abscess includes two types; skull epidural abscess and spine epidural abscess. Skull epidural abscess comes from otitis media, mastoiditis and sinusitis (6). Skull epidural abscess often accompanies with subdural abscess via emissary vein. Skull epidural space is divided by the suture of cranial bone, while subdural space expands whole brain crossing beyond the suture of cranial bone. Meanwhile subdural space is minimum in spine. Spine epidural abscess comes from local infection such as vertebral, disk infection, and/or soft tissue infection. Both epidural abscesses can occur from hematogenic seeding. As risk factors, diabetes mellitus (1-5), intravenous drug abuse, alcoholism and immunosuppressives are listed. Our patient was a massive-alcohol drinker. It might have come from hematogenic seeding.
As imaging diagnostic tools, CT and MRI are useful to know the extent of epidural abscess. MRI is more useful to demonstrate spinal epidural abscess than CT because of no artifact of bone on MRI. It is known that abscess is visualized as high signal intensity on Diffusion MRI and its ADC values are lowering. Actually, ADC values of paraspinal muscle abscess in our case were 0.70, which was compatible values to the previously reported values of ADC, 0.68 to 0.75 on spontaneous abscess (7).
Meanwhile, as for vertebral disk which is composed of collagen protein and mucoprotein, the degree of erosion is different between pyogenic spondylitis and tuberculosis spondylitis. Because mycobacterium tuberculosis lacks proteolytic enzyme (8), vertebral disk is usually preserved in tuberculous spondylitis, while because most bacteria own proteolytic enzymes, pyogenic spondylitis often erodes vertebral disk even in early phase (8-11).
Further, the degree of vertebral bone destruction is more severe in tuberculous spondylitis than pyogenic spondylitis. It is believed that the action of macrophages under tuberculous spondylitis makes the bone destruction much greater than the action of leukocytes under pyogenic spondylitis does (8-11).
【Summary】
We presented an eighty one-year-old male for high fever and with laboratory data of high values of CRP 29.7 mg/dL and white blood cells 16940/mm3. Abdomen CT and MRI revealed epidural abscess, psoas muscle abscess and paralumbar muscle abscess. Diffusion MRI showed high signa intensity corresponded to abscesses. ADC values are lowering, approximately 0.7. It is borne in mind that pyogenic spondylitis and tuberculous spondylitis make psoas muscle abscess, while epidural abscess makes paralumbar muscle abscess as well as psoas muscle abscess. Of course, pyogenic spondylitis and tuberculous spondylitis can create epidural abscess. Epidural abscess can occur from hematogenic seeding. Although subdural space covers a whole brain, subdural space in minimum in spine. Vertebral disk is usually preserved in tuberculous spondylitis, while because pyogenic spondylitis often erodes vertebral disk even in early phase. ADC values of spontaneous abscess are around 0.7.
【References】
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2021.2.3