Introduction : The benefits of a sitting position for neurosurgery involving the posterior fossa remain controversial. The main concern is the risk of venous air embolism (VAE). A recent study showed that the rate of VAE was higher when the head was elevated to 45° than when it was elevated to 30°. However, the degree of head elevation that causes clinically important VAE is unclear. The purpose of this study was to estimate the head elevation angle at which the probability of VAE is 50% by using EtCO 2 monitoring to detect of VAE. Methods : The anesthesia records of 23 patients who underwent neurosurgery in a sitting position were reviewed retrospectively. Intraoperative ventilation was set to maintain EtCO 2 at approximately 38-42 mmHg. The head elevation angle in each case was determined from a photograph taken by the anesthesiologist or brain surgeon. Nineteen of the 23 cases had photographs available that contained a horizontal reference in the background. Seven cases were treated as VAE during the operation. Six of these cases met the criteria for VAE in this study. Data analysis was performed on a total of 18 patients. The angle between the line connecting the hip joint and the shoulder joint and the horizontal reference was obtained by ImageJ software. Logistic regression was performed using the Python programming language to determine the head elevation angle at which the probability of air embolism was 50%. Results : The decision boundary in the logistic regression was 35.7°. This head elevation angle was the boundary where the probability of VAE was 50%. Conclusion : The angle of head elevation that caused clinically important VAE was estimated to be 35.7°.

We describe a rare case of asymptomatic inflammatory endotracheal polyp resolved by antibiotic treatment. Histological examination of biopsy specimens showed an inflammatory polyp consisting of fibrovascular stroma and sparse lymphocyte infiltration. The size of the polyp was unchanged during 3 months without any treatment and its etiology was unclear. Although a bacterial organism was never proven, the polyp decreased remarkably under treatment with an oral antibiotic (ciprofloxacin) and did not recur for 6 months. Antibiotic treatment may be of value for inflammatory tracheobronchial polyps in cases of unclear etiology.

We report a rare case of squamous cell carcinoma located in the middle mediastinum as a solitary mass. Histologically, lymphatic tissues remained together with nests of squamous cell carcinoma which were occupying the greater part of the mass. Examinations of the whole body failed to detect a primary site of the squamous cell carcinoma. It is considered that the carcinoma cells reflect metastasis from a primary-unknown carcinoma (most likely TO lung squamous cell carcinoma) or that they originated from benign epithelial inclusions in a mediastinal lymph node.

The semi-sitting position is well known to neurosurgeons. However, there are few reports of microvascular decompression surgery for glossopharyngeal neuralgia performed using the semi-sitting position. The semi-sitting position is not widely adopted in Japan, but it is considered to be a very useful neurosurgical position. Microvascular decompression surgery for glossopharyngeal neuralgia is a relatively rare procedure, and the semi-sitting position is very effective, considering the possibility of intraoperative cardiac arrest and postoperative complications of lower cranial nerve palsy. This report describes two cases of glossopharyngeal neuralgia operated in the semi-sitting position. Microvascular decompression was performed on both patients, and postoperative pain controls were good and no complications were observed. We show that the use of the semi-sitting position to perform microvascular decompression for glossopharyngeal neuralgia provides an excellent surgical view of the brainstem.

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