Sang Soo Eun, M.D* David Del Curto M.D* Sang-Ho Lee, M.D., Ph.D** Gun Choi, M.D., Ph.D**
of Surgery, Wales College of
University, Cardiff, United
Address for Correspondence
Gun Choi, M.D., Ph.D.,
Department of Neurosurgery,
Wooridul Spine Hospital,
47-4 Chungdam-dong Gangnam-gu,
Seoul, 135-100 Korea
Sources of Support : This study was supported by a grant from the Wooridul Spine Hospital.
We report the spontaneous resolution of Baastrup’s disease and an associated posterior epidural cyst after anterior lumbar interbody fusion and percutaneous pedicle screw fixation (ALIF and PPF). A 52-year-old male presented with radiating left calf pain, lower back pain, and neurogenic claudication. Radiographs showed the presence of Grade 2 spondylolytic spondylolisthesis of L5 over S1. MRI (Magnetic resonance imaging) showed Baastrup’s disease between the L4 and L5 spinous processes and a posterior epidural cyst at the same level with resultant canal compromise. We performed ALIF and PPF of L5 and S1. Without excision of spinous process and the cyst, postoperative MRI showed a size reduction of the cyst, which was in the upper level of the fusion segment.
Baastrup disease; bursitis; ALIF; epidural cyst
Baastrup’s disease was first described in 1933 as a condition of pathologic changes in the lumbar spine of the apposing surfaces of adjacent spinous processes and the soft tissues between them. The disease is associated with lower back pain and it develops when there is close approximation and impingement of one spinous process on another. Images show contact between adjacent lumbar spinous processes (“kissing spine”) with sclerosis, enlargement and flattening of the appositional surfaces. Bursa, with the creation of a synovial fluid, can be created in the interspinous region. Propagation of the bursa into the dorsal epidural space can result in posterior epidural cysts that may rarely cause symptomatic spinal stenosis3) and neurogenic claudication. 7) MRI is sensitive in detecting interspinous bursa formation. The condition is related to excessive lordosis causing mechanical pressure, which creates a nociceptor. Its clinical manifestation is midline extension based back pain. 2) Usually, the pain on back extension can be relieved by flexion. Treatment for Baastrup’s disease has been local anesthetic injection, and excision of part of the spinous processes.2) There have been no reports describing how anterior lumbar interbody fusion and percutaneous pedicle screw fixation (ALIF and PPF) affects Baastrup’s disease by restoration of spinal alignment. We report spontaneous resolution of the disease and an associated posterior epidural cyst after ALIF and PPF.
A 52-year-old male presented with radiating left calf pain and Grade 4 weakness in left ankle plantar flexion, which had started 1 month earlier. He also complained of lower back pain of 3-years duration. The pain was aggravated by activity, and he had developed symptoms of neurogenic claudication in the previous 6 months. Conservative treatment and selective nerve root blocks had been unsuccessful and local spinal tenderness and paraspinal muscle spasm on flexion were present. The patient stood with a stooped posture and had painful restriction of extension. Radiographs showed the presence of Grade 2 spondylolytic spondylolisthesis of L5 over S1. MRI (T2-weighted images) showed the presence of neoarthrosis between the spinous processes of L4 and L5 with associated interspinous bursitis, indicative of Baastrup’s disease (Figure 1A). Lumbar interspinous bursitis is defined as a fluid-like signal intervening between consecutive spinous processes. There was also a cyst in the midline in the posterior epidural space at the same level, with resultant canal compromise (Figure 1B, C). We planned ALIF and PPF of L5 and S1 to restore the disc height to indirectly decompress the left foramen of L5-S1 (Figure 1D). Without spinous process excision and direct decompression of the cyst, immediate postoperative MRI showed a size reduction of the cyst, which was located in the upper level of the fusion segment (Figure 2B, C). The space between the L4 and L5 spinous processes was increased (0mmà6mm)(Figure 2, 3) after fusion of the L5-S1 segment by restoration of L4 to S1 segmental lordosis(37°à 32°) and the disc height (6mmà14mm). The patient noted a significant improvement in his back pain, radiating left leg pain, and neurogenic claudication after surgery. At 3 month postoperative follow up, left ankle plantar flexion weakness improved to grade 5.
Fig. 1. MRI of L4-L5 interspnous bursitis: Baastrup syndrome in L5-S1 spondylolisthesis patient. (A) Sagittal T2-weighted lumbar spine images show interspinous bursitis (white open arrow). (B) In the posterior elements note findings at the L4-5 levels. Note high fluid signal intensity in the interspinous regions representing bursitis. Also note associated spondylosis and L4-L5 spondylolisthesis with spinal stenosis. T2-weighted axial image shows the posterior epidural cyst (black arrow) narrowing the central canal. (C) Axial T2-weighted image shows evident compression of thecal sac by posterocentral epidural cyst (arrow). (D) Left foraminal stenosis of L5-S1 showing root compression (white arrow).
Fig. 2. (A) Postoperative sagittal T2 weighted MRI shows decreased signal intensity on L4-5 interspinous spaces and increased space(black arrow) (B) The size of posterior epidural cyst(white arrow) has been markedly decreased. (C) Axial MRI image shows decreased cyst size (white arrow).
Fig. 3. (A) Preoperative lateral lumbar x-ray shows grade 2 spondylolytic spondylolisthesis at the L5-S1 level. Note apposition of L4 and L5 spinous processes with sclerosis and some flattening of the opposing spines (arrow) (B) After ALIF and PPF of L5-S1, note the restoration of spaces between L4 and L5 spinous processes.
According to a study by Maes et al5), lumbar interspinous bursitis was present in 8.2% of 539 symptomatic patients undergoing lumbar spine MRI. There were associations between the presence of Baastrup’s disease and age, central canal stenosis, disc bulging, and anterolisthesis. The association with anterolisthesis and central spinal canal stenosis may suggest that the development of bursitis could also be due to translational movements by spinous processes having contact with each other. Efforts have been made to treat Baastrup’s disease by local anesthetic injection and excision of part of the spinous processes. For presumptively diagnosed Baastrup’s disease, surgical treatment has not been shown to be effective. Beks1) treated 64 patients by partial or total excision of the spinous process and the results were not satisfactory. This suggested that segmental instability is one of the causes and it will continue to produce symptoms. Chen et al3) reported on a series of 10 cases of Baastrup’s disease associated with posterior intraspinal epidural cysts leading to varying degrees of impression on the thecal sac. Some caused central spinal stenosis and half of the patients had a connection between the interspinous bursa and the epidural cystic mass. Two cysts were dissected during surgery. The histological assessments in these cases indicated a synovial cyst in one and focal granulation tissue and fibrosis in the other. Bywaters and Evans2) documented the occurrence of a synovial membrane with a thin layer of sparse lining cells around the cavity and confirmed the presence of an adventitious bursa that was related to repeated shearing movements between adjacent spinous processes. The role of Baastrup’s disease and lumbar interspinous bursitis as a substantial nociceptor is controversial. 6),4) The majority of patients with Baastrup’s disease have substantial degenerative disc disease and facet osteoarthrosis, and these entities are more likely sources of pain and targets for treatment. From this, we can infer that correction of hyperlordosis and instability may alleviate the low back pain and decrease the size of the posterior epidural cyst. We are not sure how much this has contributed to decrease the low back pain, but expansion of space between spinous processes definitely decreased mechanical irritation and reduced the pain. Rajasekaran7) reported Baastrup’s disease causing a cyst formation of an hourglass configuration leading to epidural extension and compression of the neural elements. They have treated patients with posterior decompression and fusion. In our case, we performed ALIF and PPF without posterior decompression. Although our main surgical goal was to treat anterolisthesis and foraminal stenosis, our report shows that indirect decompression through restoration of disc height and lumbar lordosis can reduce the size of an intraspinal posterior epidural cyst, which is not at the same level. Stabilization of the segment also seems to play a role in relieving stenosis caused by the cyst. This case report has some limitations. Baastrup’s disease was an incidental finding and we are not sure if the posterior epidural cyst was the cause of the claudication, and the interspinous bursa was the cause of the back pain. However, postoperative MRI shows the reduced size of the posterior epidural cyst and increased space between previous kissing spinous processes. It is interesting that fusion of the lower level with appropriate lordosis restored upper spinous processes alignment.
Baastrup’s disease with posterior epidural cyst in the lower level spondylolisthesis can be treated by ALIF and PPF without direct posterior decompression. Considering the etiology of its pain generation, which is disc degeneration associated with instability and hyperlordosis, fusion surgery with restoration of lordosis could be a treatment option in symptomatic patients with Baastrup’s disease when conservative treatment fails.
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