Intradural Herniation of a Thoracic Disc Causing Paraplegia Coincident with Epidural Anesthesia

We report a case of intradural herniation of a thoracic disc resulting in paraplegia after leg bypass surgery under epidural anesthesia. Thoracic disc herniation resulting in paraplegia is very rare. The site of pathology was distant to the epidural catheter and presented a difficult diagnostic problem. This case illustrates the need to be aware of preexisting disease as a rare cause of postoperative paraplegia. Case Report A 74-yr-old man was admitted for evaluation of right lower extremity rest pain and a gangrenous forefoot. His past medical history included gout and myocardial infarction. He underwent a right femoral above-knee popliteal artery bypass under epidural anesthesia using 2% lidocaine and epinephrine (1:200,000 dilution). Preoperative medications included ibuprofen and oxycodone. Preoperative coagulation status was normal (prothrombin time = 10.0 s, partial thromboplastin time = 26 s). The patient was placed in a sitting position, and his back was prepared and draped. Lumbar vertebral interspace 1-2 was infiltrated with 1% lidocaine, and a 17-gauge Touhe needle was introduced and advanced using a loss of resistance technique. The epidural space was not located; however, the attempt was atraumatic. There was no blood or cerebrospinal fluid (CSF) noted during the attempt. In the same manner, lumbar vertebral interspace 4-5 was infiltrated with 1% lidocaine, and the Touhe needle was advanced using a loss of resistance technique. The epidural space was successfully located, and the epidural catheter was easily advanced and secured at 12 cm at the skin. Neither blood nor CSF was aspirated from the catheter. The initial dose was 13 mL followed by a 5-mL second and a 3-mL third dose. He had no intraoperative complications, with an estimated blood loss of 200 mL. An anesthetic level to T4 was obtained and maintained throughout the 3 1/2-h procedure. The patient received a single dose of heparin 5000 U intravenously approximately 1 1/2 h after the procedure had begun. Upon arrival in the recovery room, the patient experienced a 5-min hypotensive episode with an arterial blood pressure of 70/45 mm Hg and a heart rate of 100 bpm. There were no changes on electrocardiogram, and myocardial infarction was later ruled out on the basis of serial electrocardiograms and cardiac enzymes. Examination of the extremity revealed no signs of postoperative hemorrhage. CSF was, however, noted in the epidural catheter, and the hypotension was attributed to an intraspinal leak that responded to administration of fluids intravascularly. It is likely that the tip of the epidural catheter had perforated the dura during transport from the operating room to the postanesthesia care unit. No medication was injected into the catheter at this time. However, the catheter may have provided a conduit for local anesthetic in the epidural space to enter the intrathecal space, resulting in hypotension secondary to sympathectomy. Over the 4-h course in the postanesthesia care unit, the patient's sensory block decreased from T4 to T12 level; however, motor block of the lower extremities persisted. At this time, it was felt that this resolving block was most consistent with the effect of lidocaine as opposed to epidural hematoma or spinal cord compression. The epidural catheter was removed at this time (6 h postintraoperative intravenous heparin dose), and the patient was transferred to the surgical intensive care unit for observation. In the morning, neurological examination was normal in the upper extremities, but there was symmetrical loss of reflexes and flaccid paraplegia in the legs. The lower extremity sensation to light touch and pain returned, but persistent diminished vibratory sensation was noted. The neurosurgical department was consulted. Emergency magnetic resonance imaging scan (MRI) with T1- and T2- weighted imaging showed no evidence of epidural hematoma, but moderate spinal stenosis at the L4-L5 level with mild diffuse disc bulging at T10 and L1 was noted. The patient was given large-dose intravenous methylprednisolone. There was no clinical improvement over the next 12 h, and a repeat MRI scan revealed the same findings with no evidence of epidural hematoma or spinal cord infarction. On the second postoperative day, the neurosurgeon suggested a MRI scan of the thoracic spine to rule out spinal cord ischemia, possibly secondary to compromise of the artery of Adamkiewicz. This demonstrated the source of the paralysis (Figure 1). There was an intradural herniation of the T7-T8 disc with severe spinal cord compression. The neurosurgeon recommended urgent disc decompression, but the patient and his family refused surgery. His neurologic function remained unchanged. He was transferred to the spinal cord injury unit, and bladder catheterization and bowel care were instituted. His graft remained patent, and he underwent transmetatarsal amputation with good healing of the stump. With rehabilitation, he became independent in his daily activities using a wheelchair. He was discharged under home health care assistance. At his 3-mo clinic visit, he had regained partial use of his legs but remained wheelchair dependent.Figure 1: Thoracic magnetic resonance imaging MRI scan demonstrating intradural herniation of the T7-T8 disc (arrow).Discussion Intradural herniation of a thoracic disc resulting in flaccid paraplegia is rare [1,2]. Protruded thoracic disc with cord compression involves only 0.25%-0.75% of all cases of symptomatic intervertebral discs [3]. Transient paralysis after epidural anesthesia is estimated at 0.1% with only a 0.02% incidence of permanent paralysis [4-6]. In 1975, Usubiaga [7] provided a comprehensive review of 54 cases of paraplegia after epidural anesthesia from several causes but ultimately attributed them to one of three basic sources: a complication of anesthesia, surgery, or preexisting disease. Our case demonstrated a diagnostic challenge that included many potential causes for postoperative paraplegia. There have been several reports of cord compression from traumatic puncture or systemic heparinization and epidural hematoma formation [7-14]. Chemical toxicity is mostly related to highly concentrated solutions or rapid infusions, although certain anesthetics have also been implicated in the development of arachnoiditis [4,7]. Vascular lesions with spinal cord hypoperfusion and subsequent neurologic injury have also been reported [15,16]. Other rare causes include extradural tumors or abscess [17,18]. Exacerbation of preexisting intervertebral disc disease has been seen in rare cases after procedures in the spinal area [19,20]. With a lack of MRI findings on the initial scans and findings of lumbar disc disease, a more comprehensive MRI assessment of the thoracic spine revealed the lesion distant from the site of epidural catheter insertion. On chart review and further questioning of the patient after the event, no signs of preexisting symptomatic disc disease were found. It is uncertain whether positioning during the epidural insertion or surgery contributed to the disc herniation. Although the etiology was separate and coincidental to the block itself, manifestations of the condition were not immediately apparent due to the effects of the regional block. Collier [21] reported a case of paraplegia after epidural block and surgery related to Guillain-Barre syndrome and emphasized the need for a thorough investigation of all causes of neurologic sequelae beyond the anesthetic technique. We believe that this case emphasizes the need to be aware of preexisting disease as a rare cause of paraplegia after epidural anesthesia.