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Clinical Observations |
1 Department of Radiology, Wooridul Spine Hospital, Seoul, Republic of
Korea.
2 Department of Neurosurgery, Wooridul Spine Hospital, 47-4, Cheongdam-dong,
Gangnam-gu, Seoul 135-100, Republic of Korea.
3 Department of Pathology, Wooridul Spine Hospital, Gangnam-gu, Seoul, Republic
of Korea.
Received March 8, 2007;
accepted after revision July 18, 2007.
Address correspondence to S. H. Lee
(shlee{at}wooridul.co.kr).
Abstract
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CONCLUSION. Percutaneous CT-guided aspiration is an effective method for the management of lumbar intervertebral discal cysts.
Keywords: cyst • disk herniation • intervertebral cyst • lumber disk • percutaneous CT-guided aspiration
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MRI
MR images were obtained in the sagittal and axial planes with the use of
spinal surface coils on a 1.5-T unit (Intera, Achieva, Philips Medical
Systems). The parameters were as follows: 512 x 256 matrix, 30-cm field
of view, four signals averaged, and 4-mm section thickness with a 0.4-mm
intersection gap. Fast T1-weighted (TR/TE, 438/8) and T2-weighted (3,670/120)
spin-echo sequences were performed on all patients. Gadopentetate dimeglumine
(0.1 mmol/kg body weight) was administered IV to six patients, and images were
obtained with parameters identical to those for the unenhanced T1-weighted
sequences.
Technique of CT-Guided Aspiration
Patients were placed in the prone position. According to the requirements
of the radiologist performing the procedure and the availability of the CT
suite, the procedure was performed in aseptic conditions with CT (Somatom
Sensation Open scanner, Siemens Medical Solutions) imaging guidance. After
confirmation of the discal cyst level on axial and sagittal CT multiplanar
projection reconstructions, an 18-gauge 9-cm spinal needle was inserted
through the posterolateral route at the disk level. Ten to 15 mL of nonionic
contrast medium (300 mg I/mL iohexol, Omnipaque 300, GE Healthcare) was
injected into the epidural space by means of positioning the needle. During
puncture of the epidural space, the needle was slowly advanced with constant
spillage of contrast material that not only enabled clear visualization of the
cyst and nerve root but also displaced the thecal sac laterally, giving a
sufficient route for puncture of the discal cyst and avoidance of puncture of
the thecal sac.
CT was repeated for confirmation of the location of the needle. Under CT guidance, an 18-gauge spinal needle was inserted into the cyst through the interlaminar space (Fig. 1A, 1B). If the needle tip reached the cyst, a small amount of air or contrast material was injected into the cyst. That the tip of the needle was in the cyst was confirmed on the CT images. If the tip of the 18-gauge 9-cm needle did not reach the cyst, a 22-gauge 15-cm spinal needle was inserted into the cyst through the coaxial system. A small amount of serous or bloody fluid was aspirated from the cyst (mean volume, 3.4 mL; range, 2–5 mL). Immediately after the procedure, lower back pain, radiculopathy, and numbness in the dorsal aspect of the foot disappeared. The straight-leg-raising test returned a negative result, and muscle weakness and sensory abnormality were relieved.
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Follow-Up
Preoperative evaluations included detailed neurologic examinations, dynamic
radiologic studies of the lumbosacral spine, lumbosacral MRI, and subjective
ratings of back and radicular pain. Postoperative neurologic examinations and
telephone surveys were conducted for all patients at the follow-up times shown
in Table 1 to determine whether
new symptoms had developed since the previous clinic visit. Pain level was
evaluated with a visual analog scale (VAS) of 0–10. A score of 0
represented no pain, and a score of 10 indicated severe pain. Preprocedural
and postprocedural clinical assessments were focused primarily on the severity
of pain. Follow-up MRI was performed at varying intervals (mean, 13.2 months;
range, 3–27 months). Clinical follow-up examinations were performed a
mean of 14.7 months (range, 6–27 months) after therapeutic
aspiration.
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Statistics
The degree of VAS score improvement in each patient was calculated by
subtracting the postprocedural VAS score from the preprocedural score. The
degree of VAS score improvement was statistically assessed. A paired Student's
t test was used to compare preprocedural and postprocedural VAS
scores. These statistical analyses were conducted with SAS software version
8.1 (SAS Institute) for Microsoft Windows, and p < 0.05 was
considered to indicate a statistically significant difference.
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The mean improvement in VAS score, defined as the preprocedural to postprocedural difference, was 7.6 ± 1.0 (SD). Excellent pain relief was achieved in seven (88%) of eight patients during 6–27 months of follow-up. The VAS score decreased from 8.0 ± 1.2 before the procedure to 00.4 ± 0.8 after the procedure (improvement of 7.6 ± 1.0) (p < 0.001). Three (38%) of eight patients had eight-point; two (25%), seven-point; one (12%), nine-point; and one (12%), six-point pain improvement (Table 1). One (12%) of the patients reported recurrent radiculo pathy at the 3-month follow-up evaluation. MRI evidence confirmed the presence of recurrent disk herniation, and the patient underwent surgical treatment. In none of the eight patients did rupture of the discal cyst occur at aspiration. No complications occurred during 6–27 months of follow-up.
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The cause and pathogenesis of lumbar discal cysts remain unknown. Two hypotheses for the formation of these cysts have been suggested. Chiba et al. [8] proposed that an epidural hematoma initially formed from hemorrhage of the epidural venous plexus results from either disk herniation or an underlying disk injury. The discal cyst develops as a result of unspecified impairment in hematoma resorption. Those authors proposed this epidural hematoma theory from findings that most of the cysts they detected contained either hemorrhagic fluid or hemosiderin. In our study, histopathologic examination of the discal cysts showed small deposits of hemosiderin, and the findings serve to support the epidural hematoma theory. Kono et al. [11] reported two cases of operatively confirmed discal cysts and proposed that the pathogenesis of discal cysts is similar to that of meniscal cysts of the knee and synovial cysts of facet joints. Those authors hypothesized that a discal cyst results when focal degeneration of an intervertebral disk causes herniation of the disk with subsequent spilling of fluid from the herniated disk. The extruded fluid incites an inflammatory response that leads to reactive pseudomembrane formation and development of a discal cyst.
The clinical and radiologic differential diagnosis of an extradural space-occupying mass in the spinal canal is extensive and includes both benign and malignant entities. Several benign intraspinal cysts manifest symptoms and signs resembling those of lumbar discal herniation. Examples are synovial cysts, gas-containing ganglion cysts, and postsurgical pseudocysts. Imaging evaluation is important in the evaluation of suspected lesions because if the diagnosis can be made prospectively, minimally invasive therapy with needle puncture, as opposed to open surgical intervention, may be appropriate. Radiography is of little diagnostic value in the evaluation of lumbar intervertebral discal cysts but can be useful for excluding other conditions in the differential diagnosis. MRI is helpful for visualizing the cystic nature of the lesion and its relation to the disk and the thecal sac, narrowing the differential diagnostic possibilities. MRI reveals that an intervertebral discal cyst is a well-defined homogeneous cyst located in the ventral or ventrolateral extradural space adjacent to a herniated disk. The cyst displaces the dural sac dorsally and may even erode an adjacent vertebral body. MRI shows a lesion similar or identical to intervertebral disk herniation with low signal intensity on T1-weighted and high signal intensity on T2-weighted images. These findings are compatible with a cyst but not with disk herniation.
Management options for lumbar intervertebral discal cysts range from nonoperative to operative, depending on the symptoms. Nonoperative techniques generally involve symptomatic relief or steroid injections into the cyst. Operative management of a discal cyst is reserved for patients with persistent neurologic symptoms or severe leg pain refractory to nonoperative treatment. Decompression of the cyst contents and resection of the cyst lining and stalk have resulted in immediate and complete resolution of pain and of motor strength and sensory deficits. Successful percutaneous management of an intervertebral discal cyst has been reported [12], but the report described only one case. In our series, more cases were available. We do not use steroid injections because no strong evidence corroborates the effectiveness of steroid injections in the treatment of patients with lumbar discal cysts. When steroid injections are administered in the management of these cysts, the treatment effect of steroid cannot be differentiated from that of aspiration of the cyst.
As for the limitations of our study, all lumbar discal cysts were not confirmed with discography or surgery. We believe discography carries risk of cyst rupture, and all discal cysts had typical findings on MR images. Aspirated fluid was sent for pathologic analysis in all cases. Examination of aspirated content can confirm the presence of a discal cyst, but the lack of pathologic proof can be a serious limitation in analysis of individual lumbar discal cysts. The small sample size also was a limitation of our study. A larger number of cases and long-term follow-up are needed.
In this study, we found that CT-guided percutaneous aspiration is effective in the management of lumbar discal cysts, 88% of patients experiencing complete resolution of radiculopathy and back pain due to lumbar discal cysts. In five (71%) of seven cases, follow-up imaging more than 1 year after treat ment showed complete regression of the lumbar discal cyst. In the other two (29%) of the seven, 6-month follow-up imaging showed decreased cyst volume. In conclusion, percutaneous CT-guided aspiration is effective for the management of lumbar discal cysts.
Acknowledgments
We are grateful for the editorial assistance provided by Joel Encinas and
Youngshin Rho.
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