Background : We normalized the amplitude of motor-evoked potential (MEP) monitoring using compound muscle action potential (CMAP) generated by peripheral nerve stimulation. Anesthetic fade refers to a time-dependent decrease in the amplitude of intraoperative MEP. It is thought to result from the accumulation of propofol. We examined whether normalization by CMAP after peripheral nerve stimulation could increase the sensitivity and specificity of MEP monitoring and compensate for anesthetic fade during spinal surgery.

  Methods : Intraoperative MEP monitoring was performed in 382 spinal operations in patients without distinct preoperative motor palsy. Sensitivities and specificities with or without CMAP normalization were calculated using the receiver operating characteristic (ROC) analysis. In 1400 muscles in 378 spinal surgeries, which did not exhibit neurological motor changes after the operation, the MEP amplitude and the CMAP amplitude according to operation times were analyzed.

  Results : In 382 spinal surgeries for patients without distinct preoperative motor palsy, amplitude reductions of 77.9% and 80.6% as cutoff points for motor palsy with and without CMAP normalization resulted in a sensitivity of 100% and specificity of 96.8% and 96.5%, respectively. In 1400 muscles in 378 spinal surgeries, which did not exhibit neurological motor changes after the operation, the amplitudes of both MEP and CMAP increased over time after peripheral nerve stimulation due to the disappearance of muscle-relaxant action. After peripheral nerve stimulation, CMAP significantly increased from the beginning to the end of the operation. Anesthetic fade in transcranial MEP monitoring seemed to occur at more than 300min of surgery based on the results of a ROC analysis of the operation time and relative amplitudes. While the mean amplitude without CMAP normalization at more than 300min was significantly lower than that at less than 300min, the mean amplitude with normalization by CMAP after peripheral nerve stimulation for more than 300min was not significantly different from that at less than 300min.

  Conclusions : Although CMAP after peripheral nerve stimulation normalization did not increase the sensitivity and specificity of MEP monitoring during spinal surgery, it was able to avoid the effect of anesthetic fade. Anesthetic fade seemed to result from a decrease in synaptic transmission at the neuromuscular junction due to propofol accumulation.

  Purpose : Preoperative parameters of cervical sagittal balance, including T1 slope (T1S) and C2-C7 sagittal vertical axis (cSVA), have been recognized as predictors of kyphosis and neck disability after cervical posterior decompression surgery. However, the importance of these parameters in anterior cervical discectomy and fusion (ACDF) has not been sufficiently studied. We investigated the temporal changes in these parameters, including C2-C7 cervical lordosis (CL), cSVA, T1S, and T1 slope minus cervical lordosis (T1S-CL), after ACDF and examined the influence of ACDF on cervical sagittal balance.

  Materials and Methods : We retrospectively analyzed the clinical data of 24 patients (13 males ; 11 females ; mean age, 59.5±15.6) who underwent ACDF for up to 2 levels with a standalone polyether-ether-ketone (PEEK) cage. Patients with preoperative lordotic angles of 10° or more were allocated to the balance group, and those with angles less than 10° were allocated to the imbalance group. CL, cSVA, T1S, and T1S-CL were measured preoperatively and one year after surgery. The clinical outcomes were measured using the Japan Orthopedic Association (JOA) score, and the relationships between the JOA score and the cervical sagittal balance parameters were analyzed.

  Results : After ACDF, a cervical lordotic angle of 3.8±4.6° was lost in the balance group (CL≧10°, n = 12), whereas a cervical lordotic angle of 5.1±8.6° was gained in the imbalance group (CL<10°, n = 12) ; a significant difference was observed between the two groups.

  The analyses of all 24 cases revealed a weak correlation (r = 0.43) between the preoperative cSVA and the postoperative JOA score improvement rate at 1 year, but there were no relationships between the other parameters and the JOA score improvement rate. Moreover, a positive correlation (r = 0.66, p = 0.02) was observed between the preoperative cSVA and the JOA score improvement rate 1 year after surgery in the balance group.

  Conclusion : The effect of ACDF on cervical sagittal balance depends on the preoperative lordotic angle. In a balanced lordosis case, preoperative cSVA correlates with the postoperative JOA score improvement rate, and preoperative cSVA may be predictive of the clinical outcomes.

  A 4-year-old girl presented with severe nocturnal neck pain 2 months after mycoplasmosis. Her neck pain gradually worsened, and it often disturbed her sleep. She visited our hospital one month after onset. She had no relevant medical or family history. Although neurological examinations revealed no abnormal findings, cervical magnetic resonance imaging (MRI) showed slightly high signal intensity at the dens in the T2-weighted and diffusion-weighted images. The cervical computed tomography (CT) scan showed osteolytic changes in the dens and C2 vertebral bodies. Laboratory examination revealed inflammatory changes and increased mycoplasma antibody titers. We performed an open biopsy and diagnosed pyogenic spondylitis based on laboratory and pathological findings, which showed non-specific inflammatory changes. After receiving antibiotics for 8 weeks, her symptoms improved, and she was discharged with a neck collar. However, she developed polyuria and polydipsia one week after discharge and was diagnosed with diabetes insipidus. Head MRI revealed a well-enhanced thickened pituitary stalk. We diagnosed her with Langerhans cell histiocytosis (LCH) based on positive immunostaining for CD1a in the specimen from C2. She was transferred to the children's hospital, and chemotherapy was initiated. Two years after treatment, she improved, except for the diabetes insipidus.

  LCH is a relatively rare entity characterized by abnormal proliferation and tissue accumulation of dendritic cells with features similar to epidermal Langerhans cells in various organs. Although LCH can be diagnosed by immunostaining, it is difficult to suspect LCH from the clinical course and images of a single-system single-site type of LCH, such as the spine. It is important to keep LCH in mind as a differential diagnosis for spinal lesions in children.

  Spinal atypical meningiomas in pediatric patients are very rare, and no consensus exists regarding their characteristics, treatment, and prognosis. We report a case of this type of tumor in a 16-year-old boy who had experienced a gradual decline in muscle strength for several years and developed sudden quadriplegia after falling down the stairs. Computed tomography (CT) and magnetic resonance imaging (MRI) showed a homogeneously enhanced tumor with calcifications inside the spinal canal at C2 level, and the tumor was firmly compressing the spinal cord. Intraoperative findings revealed that the tumor was highly calcified, but there was no spinal cord invasion. Since it was an emergency, tumor resection was performed after initial preservation of adjacent roots, access to the attachment site ventrolaterally after debulking, and precise dissection through a well-defined plane from the medulla, achieving Simpson grade II resection. Histopathological examination revealed that most of the findings were consistent with meningothelial meningioma; however, some features of atypical meningioma were present, and the MIB-1 index was 11.2%. Therefore, the lesion was considered an atypical meningioma. Two years after the surgery, there was no recurrence. Because of its pathological grade and no excision of the attachment dura, careful follow-up is required.

  Headaches often occur after a lumbar puncture, and it is considered to be caused by cerebrospinal fluid leakage from the puncture site. A 24-year-old woman presented to our hospital with a headache and fever and underwent a lumbar puncture to investigate meningitis. She complained of severe headache and back pain after the procedure. Here, we report a case of extensive cerebrospinal fluid retention in the thoracic epidural space confirmed through magnetic resonance imaging (MRI).

  A 24-year-old woman with fever (body temperature, approximately 39℃) and headache presented to our hospital and was admitted to the neurosurgery outpatient clinic for the diagnosis of meningitis. Lumbar puncture was performed using a 22-G spinal needle. The cerebrospinal fluid was drained in one puncture, and approximately 5ml of cerebrospinal fluid was collected. The procedure ended without complications. However, she had severe orthostatic headache and back pain the next day ; therefore head MRI and spinal MRI were performed. Head MRI showed mild-enhancement of the dura mater, whereas spinal cord MRI showed a large amount of cerebrospinal fluid retention at the dorsal epidural area of the spinal cord in the thoracic spine but not in the lumbar spine. Her symptoms improved with infusion and rest alone, and a blood patch was not necessary. Two weeks later, MRI was performed, and it was confirmed that cerebrospinal fluid retention had resolved. After the lumbar puncture, MRI of the area surrounding the puncture site, as well as the cervical and thoracic vertebrae, is useful for diagnosing cases of cerebrospinal leakage.

  Extradural spinal meningiomas (EDSMs) are extremely rare, and most literature on these lesions have been case reports and short case series. We report a case of cervical EDSM in a 76-year-old woman with right hemiparesis due to a previous cerebral infarction. She had fallen and sustained a Th12 vertebral compression fracture 2 months before admission and had since been bedridden. Around the same time, she became aware of weakness in her left upper and lower limbs, but magnetic resonance imaging (MRI) did not reveal any new structural lesions in the brain. Although she had continued rehabilitation for 3 months, her weakness gradually worsened. Eventually, she developed tetraplegia following severe neck pain approximately a month before admission. On admission, she was nearly completely tetraplegic and had severe pain across the neck that radiated to the left upper limb. She complained of numbness below Th1 ; her pinprick and light touch sensations had reduced to 2—3/10 in the left lower extremity. Her neurosurgical cervical spine score was 1 : 1 : 1 : A, and the Japanese Orthopaedic Association cervical score was 2.

  MRI revealed a left-dominant extradural mass extending from the C3 to C5 vertebral level and compressing the spinal cord anterolaterally. Computed tomography at C4 showed an enlargement near the left neural foramen, which was overlooked preoperatively.

  Based on the provisional diagnosis of an extradural hematoma, laminectomy was performed from C3 to C5. The surface of the dura was found to be covered by a sheet-like yellowish-white mass that adhered around the left C3/4 intervertebral foramen. Histopathological examination revealed meningothelial meningioma. The postoperative course was uneventful, but the neurological symptoms did not change after the procedure.

  EDSMs are thought to arise from the nerve root sheath ; it has been reported that recurrence and regrowth are likely due to difficulties with removing the tumor completely. EDSM radiologic findings also overlap with those of several other types of common extradural spinal masses, including metastatic tumors and schwannomas. In this case, the urgent need for decompression necessitates treatment without sufficient preoperative information, which can happen in an emergency. Therefore, in describing this rare case, we also wish to highlight the pitfalls in the differential diagnosis of EDSM.

  Fracture of the anterior arch of the atlas is a rare complication of foramen magnum decompression (FMD) for Chiari malformation. We report a case of a fracture of the anterior arch of the atlas after FMD. A 42-year-old woman was referred to our hospital from a nearby clinic where Chiari malformation and syringomyelia were incidentally detected during head magnetic resonance imaging (MRI) examination for headache. We performed FMD and tonsillectomy for the Chiari malformation. The patient had an uneventful postoperative course and was in good condition when discharged. She developed neck pain without any preceding incident approximately 7 months after surgery. Subsequently, she experienced neck pain during flexion, extension, and sneezing. Neck computed tomography (CT) performed at a nearby clinic revealed a fracture of the anterior arch of the atlas, and she was referred to our hospital once again. Although neck radiography did not confirm an instability of the craniocervical junction, the neck pain progressed ; thus, posterior atlantoaxial fusion was performed. Due to the thinning of the C2 vertebral pedicles, part of the C2 vertebral arch was removed during FMD, and pars screws were inserted into the C2 vertebra with lateral mass screws inserted into the C1 vertebra. The subsequent postoperative course was uneventful. Three cases have been reported in the literature, and the mechanism of injury (e.g., trauma) was not confirmed in all of them. Posterior fusion was used in 2 cases, external immobilization with a halo vest was used in 1 case, and fracture healing was achieved with a good prognosis in all three cases. When neck pain develops a few months after FMD, fracture of the anterior arch of the atlas should be suspected and preferably confirmed using CT.