Anosov N.A., Parfionov V.E., Toptygin S.V.
Chair of Rentgenology and Radiology, Clinic of Neurosurgery Medicomilitary Academy, St.Petersburg, Russia
Degenerative-dystrophic lesions are the most frequent disease of the spine [3, 5, 11]. The last 15 years were characterized by a growth of morbidity. This makes the problem of diagnosis, treatment and prevention of degenerative-dystrophic lesions of the spine a national task .
Radiation methods and MRI play an important part in diagnosis of diseases of the spine [1, 2, 5, 6, 7, 8, 10]. Spiral CT has been used in clinical practice since 1989 .
The goal of the present work is generalization of experience of using spiral CT (SCT) in diagnosis of degenerative-dystrophic lesions of lumbar spine, causing chronic pain.
Examination of 752 patients with chronic pain of lumbar localization was carried out. Obtained data were analyzed. X-ray, CT and MRI examinations showed, that degenerative-dystrophic lesions of lumbar spine were typical of all patients; 503 of them (75,9%) had this or that degree of intervertebral disk prolapse; 59 cases underwent subsequent surgical intervention. A mean age of patients was 44.4±0.4 years.
Examination was carried out with the help of Somatom Plus 4 computer tomograph (120 kV, 206 mAs, 0.75-1.0 s), using layer-by-layer and or spiral modes. When the first mode was used, a slice thickness and a step were equal to 2 mm in a plane parallel to a disk under examination. In spiral mode one or 2-3 vertebral segments (a "block") were scanned. In this case a slice thickness could reach 2, 3, 5 mm with a step of 3, 4.5 and 7.5 mm respectively. An examined area varied from 5 up to 35 cm, depending on a slice thickness, speed of scanning and current intensity. When some spinal segment were examined in "block", additional information on structures of the vertebral column, paravertebral tissues was obtained from high-quality MPR (multi-planar volume reformating), i.e. multi-planar (including curvilinear) reconstructions, and SSD (shaded surface display), i.e. three-dimentional surface reconstructions.
Tomograms of the whole population of patients with chronic pain syndrome of lumbar localization were analyzed. The results were as follows:
As for localization, there were:
The size of hernias was irrespective of their level and varied from 4 mm up to 8 mm. Posterior median and median-lateral hernias of more than 9 mm were verified in 20% of patients at the level of L4 - L5 and L5-S1 disks; they were lateral in 13% of cases. As for local prolapse of disks of 4 mm and more, their rate increased in craniocaudal direction: L2 - L3 - 8.3%, L3 - L4 - 12.8%, L4 - L5 - 43.2%, L5 - S1 - 75%, L6 - S1 - 100%.
It is known, that hernia of an intervertebral disk is its protrusion beyond the levels of adjucent terminal plates. Hernias are subdivided into disk protrusion, disk extrusion (prolapse) and sequester. Disk protrusion is local protrusion of nucleus gelatinosus within the levels of a fibrous ring. Besides, this notion includes diffuse prolapse, when disk protrusion is even along the whole circumference or posterior and lateral surfaces (fig.1). Prolapse (extrusion) takes place in case of destruction of a fibrous ring, but the prolapsed part of a disk is held by the posterior longitudinal ligament (fig.2). ŃSequester is a disk fragment, having no connections with its mother part and localized in a subligamental area epidurally or subdurally, which is an extremely rare case (fig.3,4).
CT signs of hernia of an intervertebral disk include:
Degenerative-dystrophic changes of intervertebral disks, diagnosed during CT-examination, are often accompanied by epidural fibrosis. It is a soft-tissue component (25-60 H units) in the epidural space, formed as a result of aseptic response to the degenerative process (external meningitis, lesion of the posterior longitudinal ligament) or a resorbing part of hernial prolapse, impregnated with vessels and, probably, containing calcium (fig.5,6). Epidural fibrosis, occupying 4-30 mm, was watched in almost 1/3 of examined patients with degenerative-dystrophic lesions of the spine (31%). An average length of fibrosis was 10.6±0.4 mm. Mass-effect was observed in 71.1% of cases with this or that degree of prolapse. Its rate was reliably higher (c2 = 10.727; p<0.001), than in patients with no disk hernia. Presence of epidural fibrosis in patients with disk hernias was connected directly with a degree of their prolapse and a value of reserve space within the vertebral canal. That was why a response of epidural fat to parts of prolapsed pulpous nucleus was watched very well in lower segments of the vertebral canal, where a diameter of dural sac became smaller and an amount of epidural fat grew (fig.7,8). Thus, fibrosis was observed in 16% of cases at the level of L2-L3 and L3-L4. This figure was equal to 32.6% at the level of L4-L5 and to 47.5% at the level of L5-S1.
From the point of view of a neurosurgeon, it is very important to know not only a cause, level and localization of neural compression, but also to be ready for intraoperative findings in order to ensure complete removal of compressing substrate without limiting himself to "free" fragments of a disk (fig.9,10).
Sequestration of disk hernias was identified in 8.2% of patients, included into our study. Complete sequestration was watched in 14.6% of cases; sequestered fragments were connected with a disk and localized in the subligamental space, migrating caudally, in 85.4% of patients. It was confirmed during operations. It should be noted, that epidural fibrosis was verified in 90.2% of cases with sequestered disk hernias.
A size of sequesters, measured craniocaudally, varied from 2-3 mm up to 18-21 mm. An average value was equal to 4.5±1.7 mm. Two other measurements (anteroposterior and transverse size), as well as calculation of an area of the vertebral canal in its fixed and mobile (at the level of a disk hernia) parts, were used for estimating a value of disk prolapse and a degree of narrowing of the vertebral canal, caused by hernia. The greatest number of sequesters was typical of L4-L5 disk (70.7%) and L5-S1 disk (24,4%). As for L3-L4 disk, this index was equal only to 4.9% (fig.11,12)..
We diagnosed only "fresh" sequesters with homogenous density at the level of L3-L4; 1/3 of sequestered hernias had signs of consolidation at the level of L4-L5; 50% of all sequesters at the level of L5-S1 were of heterogenous structure. May be, a cause of increase of a number of "old" sequesters in caudal direction lies in presence of large reserve space, allowing to smooth over neurologic symptoms for some period of time.
Central stenosis of the lumbar canal, caused by osteal components of its wall, was identified in 60 patients (10.1%); 27 (4.5%), 16 (2.7%) and 17 (2.9%) of them had congenital, acquired and combines stenoses respectively (fig.13,14). Absolute stenosis was observed in 10 cases (1.7%); 30 (5.1%) patients had central relative stenosis. Lateral stenoses were present in 28 (4.7%) patients; it was bilateral in almost a half of them. As for one-sided lateral stenosis, the rate of its localization on the left was two times higher (30.8%). Narrowing of the vertebral canal was caused by ossification of the affected posterior longitudinal ligament, calcification of disk hernias and their combination in the majority of cases (25.3%) (fig.15,16), (fig.17).
Stenosis of the vertebral canal, caused by non-osteal components of its walls, was verified in 59 patients, operated for discogenic neural compression. A size of posterior-median and median-lateral hernias, measured in operated patients in anteroposterior direction, varied from 9 up to 13 mm and more. Acquired discogenic degenerative stenosis was associated with congenital stenosis of the vertebral canal in 12 of them (20.3%). Degenerative changes of intervertebral disks, yellow and posterior longitudinal ligaments conditioned stenosis of the central canal in 43 cases (72,8%); lateral stenosis was watched in 16 (0.4%) patients (fig.18).
Examining patients with radiculomyeloischemic lesions, we used both conventional methods and bolus intravenous administration of contrast substance into ascending branches of common iliac arteries with subsequent scanning of the lumbosacral spine. It allowed to verify additional inferior radiculomedullary artery in 3 (10.7%) out of 28 cases (fig.19-20), (fig.21-22).
Results of examination of patients with chronic pain syndrome in the lumbosacral area showed, that it was conditioned by degenerative-dystrophic changes of the spine. The most frequent causes of pain in the back and lower extremities, progression of neurologic deficit in degenerative-dystrophic lesion of the lumbar spine are hernia of an intervertebral disk, isolated stenosis of the vertebral or root canal, segmental instability of spinal locomotor segments and degenerative spondylolisthesis.
Examination of patients with the help oh Somatom Pus 4 apparatus confirmed, that spiral CT is one of the main and most available means of diagnosis of degenerative-dystrophic lesions of the spine, manifesting themselves in narrowing of the vertebral (and lateral) canal.
Spiral CT possesses high speed of scanning, possibility to examine the spine at a considerable length and to obtain high-quality reconstructions (multi-plane and three-dimensional superficial). Thus, it allows to visualize not only minimum changes of bone tussie, but also to identify initial changes in intervertebral disks and paravertebral tissues, to differentiate structures of the vertebral canal, a degree of disk prolapse, its sequestration and to estimate peculiarities of blood supply of horse's tail roots and causes of vascular compression without applying expensive paramagnetic devices.
While carrying out preoperative examination of patients with radiculomyeloischemic syndromes, one should pay attention to a paravertebral area in a "zone of exit" of a nerve root with the purpose of studying causes of possible compression of radiculomedullary arteries.
Spiral CT allows to reduce radiation load on a patient (1.7-2.4 times lower, depending on an length of examined segment) and load on an X-ray emitter.