INTRODUCTION
Lumbar stenosis is a common disease in the elderly
23). The number of patients with lumbar stenosis complaining of low back pain, lower extremity pain and/or numbness, and neurogenic intermittent claudication (NIC) has increased yearly
11.16). The etiologies of symptomatic lumbar stenosis include nerve root compression and the disturbance of blood flow (ischemia or congestion of vessels), etc. which surround neural system
10,13).
The factors caused nerve compression are hypertrophied ligamentum flavum, facet joints, and thickened lamina. We often observed congestion of epidural veins (epidural venous varicosity) after removing the factors, intraoperativelly. Therefore, we have started this study which focuses on epidural venous varicosity.
Until now, epidural venous varicosity was rarely introduced as a factor that causes clinical symptoms
16). However, there are several studies
3,5,6,8,18,20) suggesting that epidural venous varicosity results in radiating pain through lower extremity, motor weakness, low back pain as well as NIC
3,20). Therefore, few authors insist that the removal of epidural venous varicosity is necessary during the operation
5,8,20). However, there is a controversy about how to manage the congestion of the epidural vein observed in operation field
6,20).
This study is originated from the hypothesis that epidural venous varicosity causes clinical symptoms, supported by numerous study reports and clinical experience
2). We would like to highlight evidence that epidural venous varicosity results in neurologic symptoms and the relation between epidural venous varicosity and neural structure observed during the surgery. Based on our experiences, we also propose a new classification of epidural venous varicosity.
DISCUSSION
Lumbar stenosis is defined as a degenerative disease which causes narrowing of spinal canal. Surgical management of lumbar stenosis aims to remove the anatomical structures compressing neural structures and thereby relieving the compression.
However, it is commonly observed that the congestion of internal vertebral epidural venous plexus still remained even after the elimination of those structures in lumbar stenosis operation. The remained congestion of the internal vertebral epidural venous plexus is generally defined as an epidural venous varicosity
20).
There are a number of researches regarding epidural venous varicosity. The prevalence of epidural venous varicosity is reported to be low. Recently, Slin'ko EI and colleagues
20) performed operations on 1091 patients with degenerative lumbar diseases. Of them, 48 patients showed epidural venous varicosity and thus they reported the prevalence of 4.4%
20). However, those data are thought to be underestimated because epidural venous varicosities are easily accidentally ruptured during operation. For this reason, the authors tried to perform the operation with minimum injuries to epidural venous varicosity. As a result, epidural venous varicosities were observed during the operation in most patients with lumbar stenosis in this study.
Symptoms caused by lumbar epidural venous varicosity include NIC, lower extremity radiating pain, and motor weakness. The mechanism of the development of NIC has been studied in many researches
6,7,18). Some studies showed that changes in postures led to changes in diameter of spinal canal
10). However, in the recent studies by Porter and colleagues
19) and Takahashi and colleagues
21), it was reported that epidural venous varicosity led to the development of NIC
19,21). The veins surrounding the nerve root were primarily drained to the intervertebral foramen
19,21). If the venous drainage through intervertebral foramen was impaired, it resulted in the congestion of vein drained from conus medullaris. As a result, the subsequent reduction of blood flow led to the development of NIC
19,21). This is the evidence that NIC is closely related with blood flows. For these reasons, a higher blood flow is required to meet an increased oxygen demand in walking and insufficient blood flow consequently results in NIC.
Lower extremity radiating pain may also be arisen from epidural venous varicosity according to Genevay and colleagues
6) Furthermore, epidural venous varicosity may cause other clinical symptoms such as motor weakness and myelopathy
3,4). Two mechanisms are described in order to explain the involvement of epidural venous varicosity in these clinical symptoms
5,8,20). The first mechanism is that venous congestion causes such clinical symptoms by compressing the theca sac and the nerve root. The second one is that a high pressure of epidural venous varicosity is transmitted to the perimedullary veins drained from the conus medullaris causing gradual myelopathy and neuropathy. Most authors consider that neurogenic symptoms are developed when the nerve root is compressed or stimulated by congested veins
3,4,5,8,20). Back pain caused by epidural venous varicosity is common, but the mechanism is not yet known
3,4,5,8,20).
Although there are numerous case studies reporting that an epidural venous varicosity results in clinical symptoms, most researchers have doubts in the clinical importance of epidural venous varicosity. In other diseases, the venous congestion is known to cause clinical symptoms. The most frequent symptom is trigeminal neuralgia. It is caused by the compression and stimulation of the trigeminal nerve by the petrosal vein
1,7). Sciatic neuralgia may also be developed, if lower extremity varices compresses the sciatic nerve
9,22). The aforementioned two cases support the fact that epidural venous varicosity is a sufficient source of neurogenic symptoms.
In addition, some authors published case reports about venous varicosity which was formed by other factors than degenerative diseases in lumbar spine and caused clinical symptoms. The symptoms were mainly radiculopathy or NIC. Epidural venous varicosity may be occurred in pregnancy, cardiomyopathy, portal hypertension, trauma and inferior vana cava thrombi
16).
Diagnosing of epidural venous varicosity is difficult and generally overlooked. Computed Tomography (CT), MRI with or without enhancement
3), Magnetic resonance phlebography (MRP)
12,14), CT myelography
20) can be used as diagnostic techniques. Although MRI is described as the most accurate technique in detecting epidural venous varicosity, it is difficult to identify epidural venous varicosity because of herniated disc which looks similar to epidural venous varicosity on MRI images at the same site
5,7,19). The limitation of this study lies on the fact that other diagnostic studies were not performed apart from preoperative MRI.
Other authors diagnosed epidural venous varicosities using the aforementioned test methods and classified the types in diverse methods. Slin'ko EI and colleagues
20) classified epidural venous varicosity using preoperative MRI and venography
20). Varices were classified segmentary varices, local varices, extensive varices
20). Hanley and colleagues
8) divided epidural venous varicosity into three types based on radiological findings and anatomical pathology
8). Manaka and colleagues
14) classified abnormal epidural venous varicosity seen on MRP into five types, associated with NIC
14). Morikawa and colleagues
15) classified epidural veins based on the patterns of contrast enhancement on MRI
15).
However, there are no papers classifying accurate types of epidural venous varicosity based on the observation during operations. We propose a new classification system designed to describe the relationship between the nerve root and the epidural venous varicosity. The classification system is based on the observation from the operative field and there are four patterns. We thought that clarifying the relationship between nerve roots and epidural veins is more important than identifying the names of individual veins. It is worthwhile for surgeons to understand the relationship between nerve roots and epidural venous varicosity.
As it was mentioned above, more successful outcome was shown in type C than other types. However, it was not statistical significance. It is difficult to understand an accurate relationship between types of varice and neurological symptoms because of numerous related variables that cause neurologic symptoms.
Many reports describe appropriate managements for each type of epidural venous varicosity. Hanley and colleagues
8) removed epidural varices using electric cautery or excision in all five patients with symptoms caused by epidural venous varicosity
8). After the operation, all patients were relived of symptoms
8). According to published papers, in the majority of cases, the interventions led to a positive clinical result with resolution of the neurological symptoms
20,24). In this study, removal of epidural venous varicosity was done in consideration of lumbar epidural venous system anatomy. Among epidural veins, anterior longitudinal veins and intervertebral veins are related with nerve roots. Therefore, only these veins were removed, not retrocorporeal veins. By preserving the retrocorporeal veins, obstruction of venous drainage due to the removal of the epidural venous varicosity could be avoided. In our study, NIC was alleviated in most patients as well as other symptoms.