The Incidence, Volume, Absorption, and Timing of Supratentorial Pneumocephalus During Posterior Fossa Neurosurgery Conducted in the Sitting Position

Comparison of Postoperative Seizures Between Burr-Hole Evacuation and Craniotomy in Patients With Nonacute Subdural Hematomas: A Bi-Institutional Propensity Score-Matched Analysis

BACKGROUND AND OBJECTIVES

Postoperative seizures are a common complication after surgical drainage of nonacute chronic subdural hematomas (SDHs). The literature increasingly supports the use of prophylactic antiepileptic drugs for craniotomy, a procedure that is often associated with larger collections and worse clinical status at admission. This study aimed to compare the incidence of postoperative seizures in patients treated with burr-hole drainage and those treated with craniotomy through propensity score matching (PSM).

METHODS

A retrospective cohort analysis was conducted on patients with surgical drainage of nonacute SDHs (burr-holes and craniotomies) between January 2017 to December 2021 at 2 academic institutions in the United States. PSM was performed by controlling for age, subdural thickness, subacute component, and preoperative Glasgow Coma Scale. Seizure rates and accompanying abnormalities on electroencephalographic tracing were evaluated postmatching.

RESULTS

A total of 467 patients with 510 nonacute SDHs underwent 474 procedures, with 242 burr-hole evacuations (51.0%) and 232 craniotomies (49.0%). PSM resulted in 62 matched pairs. After matching, univariate analysis revealed that burr-hole evacuations exhibited lower rates of seizures (1.6% vs 11.3%; P = .03) and abnormal electroencephalographic findings (0.0% vs 4.8%; P = .03) compared with craniotomies. No significant differences were observed in postoperative Glasgow Coma Scale (P = .77) and length of hospital stay (P = .61).

CONCLUSION

Burr-hole evacuation demonstrated significantly lower seizure rates than craniotomy using a propensity score-matched analysis controlling for significant variables.

Semisitting position for cerebello-pontine angle surgery: Analysis of complications and how to avoid it

OBJECTIVE

To analyze the primary complications related to semisitting position in patients undergoing cerebelo-pontine angle surgery.

METHODS

Retrospective data analysis from patients undergoing elective tumoral cerebelo-pontine angle surgery in a semisitting position. The incidence, severity, occurrence moment, treatment, duration, and outcomes of venous air embolism (VAE), pneumocephalus, postural hypotension, and other complications were recorded. Neurointensive care unit (NICU), length of stay (LOS), hospital LOS, and modified Rankin scale scores were calculated six months after surgery.

RESULTS

Fifty patients were operated on. Eleven (22%) presented VAE (mean duration 8±4.5min): five (10%) during tumor resection, and four (8%) during dural opening. Ten (20%) were resolved by covering the surgical bed, air bubbles aspiration, jugular compression, and one (2%) tilted to a steep Trendelenburg position. One (2%) had intraoperative hemodynamic instability. The only variable associated with VAE was meningioma at histopathology OR=4.58, p=0.001. NICU was higher in patients with VAE (5.5±1.06 vs. 1.9±0.20 days, p=0.01). There were no differences in the Rankin scale. All patients presented postoperative pneumocephalus with a good level of consciousness, except one (2%) who required evacuation. Seven patients (14%) showed postural hypotension, three (6%) after positioning, and one (2%) after developing a VAE; all were reversed with usual vasoactive drugs. No other position-related complications or mortality were registered in this series.

CONCLUSIONS

The semisitting position is a safe option with the knowledge, prevention, detection, and early solution of all the possible complications. The development of VAE rarely implies hemodynamic instability or greater disability after surgery. Postoperative pneumocephalus is very common and rarely requires evacuation. Excellent cooperation between anesthesia, nursing, neurophysiology, and neurosurgery teams is essential to manage complications.

Intracranial Air Absorption through Arachnoid Granulation: New Considerations from Transsphenoidal Surgery and Implications for Neurofluid Dynamics

Postsurgery intracranial air usually diminishes, presumably merging with cerebrospinal fluid (CSF) and venous circulation. Our study presents two transsphenoidal surgery cases, highlighting potential air absorption by arachnoid granulation (AG)-an underexplored phenomenon. AG has long been deemed pivotal for CSF absorption, but recent perspectives suggest a significant role in waste clearance, neuroinflammation, and neuroimmunity. These cases may stimulate renewed research on the multifaceted role of AG in neurofluid dynamics and potentially elucidate further AG functions.

The semi-sitting position in patients with indwelling CSF shunts: perioperative management and avoidance of complications

OBJECTIVE

Posterior fossa or midline tumors are often associated with hydrocephalus and primary tumor removal with or without perioperative placement of an external ventricular drain (EVD) is commonly accepted as first-line treatment. Shunting prior to posterior fossa surgery (PFS) is mostly reserved for symptomatic cases or special circumstances. There are limited data regarding the anticipated risk for symptomatic pneumocephalus and the perioperative management using the semi-sitting position (SSP) in such a scenario. Here, we therefore assessed the safety of performing PFS in a consecutive series of patients over a period of 15 years to allow the elaboration of recommendations for perioperative management.

METHODS

According to specific inclusion and exclusion criteria a total of 13 patients who underwent 17 operations was identified. Supratentorial pneumocephalus was evaluated with semiautomatic-volumetric segmentation. The volume of pneumocephalus was evaluated according to age and ventricular size.

RESULTS

Ten of the 13 patients had a programmable valve (preoperative valve setting range 6-14 cmH20; mean 7.5 cmH20) while 3 patients had non programmable valves. A variable amount of supratentorial air collection was evident in all patients postoperatively (range 3.2-331 ml; mean 122.32 ml). Positive predictors for the volume of postoperative pneumocephalus were higher age and a preoperative Evans ratio > 0.3. In our series, we encountered no cases of tension pneumocephalus necessitating an air replacement procedure as well as no obstruction, disconnection, infection or hardware malfunction of the shunt system.

CONCLUSIONS

Our findings indicate that a CSF shunt in situ is not a contraindication for performing PFS in the semi-sitting position and it does not increase the pre-existing risk for postoperative tension pneumocephalus. In cases of primary shunting for hydrocephalus associated with posterior fossa tumors a programmable valve set at a medium opening pressure with a gravitational device is a valid option when PFS in the semi-sitting position is opted. In patients with an indwelling shunt diversion system special caution is indicated in order to prevent and detect overdrainage especially in not adjustable valves or shunts without antisiphon devices.

Puerto Rico Recurrence Scale: Predicting chronic subdural hematoma recurrence risk after initial surgical drainage

Background:

Chronic subdural hematoma (CSDH) commonly affects older individuals and is associated with a relatively high rate of recurrence after surgery. Many studies have created grading systems to identify patients at high risk of CSDH recurrence after the initial surgery. However, no system has been adopted widely. The authors present the first CSDH grading system created from a population-based single-center data set.

Methods:

A single-center Puerto Rican population-based retrospective analysis was performed on consecutive patients treated for a CSDH at a designated institution from July 1, 2017 to December 31, 2019. Univariate and multivariate analyses were used to create a CSDH recurrence grading scale. Retrospective validation was conducted on this sample population.

Results:

The study included 428 patients. Preoperative midline shift, postoperative midline shift, and size of postoperative subdural space differed between the recurrence and nonrecurrence groups (P = 0.03, 0.002, and 0.002, respectively). A multivariate analysis was used to create a 10-point grading scale comprising four independent variables. Recurrence rates progressively increased from the low-risk (0–3 points) to high-risk (8–10 points) groups (2.9% vs. 20.3%; P < 0.001).

Conclusion:

A 10-point grading scale for CSDH recurrence was developed with four components: preoperative midline shift (≤1 and >1 cm), laterality (bilateral, unilateral-right, and unilateral-left), size of postoperative subdural space (≤1.6 and >1.6 cm), and pneumocephalus (present or absent). Patients who scored higher on the scale had a higher risk of recurrence. This CSDH grading scale has implications for Puerto Rico and the general population as the elderly population increases worldwide.

[Sitting position in neurosurgery: realizing the risks]

The author discusses potential intraoperative complications following neurosurgical interventions in sitting position: venous air embolism and paradoxical air embolism, postural hypotension, pneumocephalus, cervical flexion neuropathy, positional damage to peripheral nerves and others. Naturally, prevention of these complications is also considered, and the most effective approach is surgery in lying position.

Occurrence and management of postoperative pneumocephalus using the semi-sitting position in vestibular schwannoma surgery

Background

The semi-sitting position in neurosurgical procedures is still under debate due to possible complications such as venous air embolism (VAE) or postoperative pneumocephalus (PP). Studies reporting a high frequency of the latter raise the question about the clinical relevance (i.e., the incidence of tension pneumocephalus) and the efficacy of a treatment by an air replacement procedure.

Methods

This retrospective study enrolled 540 patients harboring vestibular schwannomas who underwent posterior fossa surgery in a supine (n = 111) or semi-sitting (n = 429) position. The extent of the PP was evaluated by voxel-based volumetry (VBV) and related to clinical predictive factors (i.e., age, gender, position, duration of surgery, and tumor size).

Results

PP with a mean volume of 32 ± 33 ml (range: 0–179.1 ml) was detected in 517/540 (96%) patients. The semi-sitting position was associated with a significantly higher PP volume than the supine position (40.3 ± 33.0 ml [0–179.1] and 0.8 ± 1.4 [0–10.2], p < 0.001). Tension pneumocephalus was observed in only 14/429 (3.3%) of the semi-sitting cases, while no tension pneumocephalus occurred in the supine position. Positive predictors for PP were higher age, male gender, and longer surgery duration, while large (T4) tumor size was established as a negative predictor. Air exchange via a twist-drill was only necessary in 14 cases with an intracranial air volume > 60 ml. Air replacement procedures did not add any complications or prolong the ICU stay.

Conclusion

Although pneumocephalus is frequently observed following posterior fossa surgery in semi-sitting position, relevant clinical symptoms (i.e., a tension pneumocephalus) occur in only very few cases. These cases are well-treated by an air evacuation procedure. This study indicates that the risk of postoperative pneumocephalus is not a contraindication for semi-sitting positioning.

Significance of intracranial gas on post-mortem computed tomography in traumatic cases in the context of medico-legal opinions

The detection of intracranial gas (ICG) in people who died due to trauma became possible once postmortem computed tomography (PMCT) became available in addition to traditional post-mortem examinations. The aim of this study was to determine the importance of ICG in the context of medico-legal opinions. We assessed 159 cases of trauma-induced death. Cadavers with pronounced signs of decomposition, open skull fractures, and after neurosurgical operations were excluded. Both PMCT findings and data from autopsy reports were analyzed. ICG was found in 38.99% (n = 62) of the cadavers, 96.77% (n = 60) of which presented with pneumocephalus (PNC) and 40.23% (n = 25) with intravascular gas (IVG). There was a strong correlation between ICG and skull fractures/brain injuries, as well as chest injuries, especially lung injuries. In 13 cases, ICG presented without skull fractures; three of these cases died as a result of stab and incised wounds to the neck and chest. The mean time between trauma and death was significantly longer in the non-ICG group than the ICG group at 2.94 days (0–48 days) and 0.01 day (0–1 day), respectively (p < 0.0001). The presence of ICG is a result of severe neck and chest injuries, including stab and incised wounds. The victims die in a very short amount of time after suffering trauma resulting in ICG. The ability to demonstrate ICG on PMCT scans can be of significance in forming medico-legal opinions.

A prospective randomized clinical trial to evaluate the impact of intraoperative ventilation with high oxygen content on the extent of postoperative pneumocephalus in patients undergoing craniotomies

Purpose of the article: To determine whether intraoperative ventilation with pure oxygen during the last stage of surgery reduces the occurrence and volume of postoperative pneumocephalus when compared to conventional air/oxygen mixture in patients undergoing craniotomy.

MATERIAL AND METHODS

prospective randomized single-blinded study to compare the rate of occurrence and volume of postoperative pneumocephalus in patients undergoing craniotomy receiving intraoperative ventilation with pure oxygen (Group B) versus a conventional air/oxygen 1:1 mixture (Group A) during the last stage of surgery. This trial was registered in ClinicalTrials.gov #NCT02722928, protocol number 2015H0032.

RESULTS

One hundred patients were randomized into group 'A' and group 'B'. Seventy patients were included in the final analysis with 39 patients allocated in group 'A' and 31 patients in group 'B'. Median and IQR were used for postoperative penumocephalus volume. Group A: 9.65 [3.61-23.20]; Group B: 7.06 [2.70-20.1]. Our study showed no prophylactic effect on postoperative pneumocephalus volume when using mechanical ventilation with higher oxygen concentrations than the standard FiO₂ during the last stage of surgery in patients undergoing craniotomy (p = .47). No statistical difference was found in SICU LOS between groups (median 1,380 min [group A] versus 1,524 min [group B]; p = .18).

CONCLUSION

The use of intraoperative mechanical ventilation with pure oxygen was not associated with a prophylactic effect on the occurrence and extent of postoperative pneumocephalus in our patient setting. Published literature describing the extent of postoperative pneumocephalus is limited or highly variable among institutions.

Predictors of ventricular tension pneumocephalus after posterior fossa surgery in the sitting position

BACKGROUND

Ventricular pneumocephalus is a rare but potentially life-threatening complication of cranial surgery in the sitting position.

OBJECTIVE

The objective of the study is to assess the incidence and risk factors of postoperative ventricular pneumocephalus.

METHODS

We performed a retrospective chart review of 307 consecutive patients (147 men, 160 women) treated at our institution by intracranial surgery in the sitting position from January 2010 to October 2014. Ventricular air entrapment with lack of arousal or neurologic deterioration requiring external ventriculostomy (EVD) was defined as ventricular tension pneumocephalus (VTP). Demographic variables were recorded along with radiological and clinical data. The occurrence of pneumocephalus was correlated with patient-related and surgical variables.

RESULTS

VTP was observed in 12 cases (3.9%). These patients had higher intraventricular air volumes (48.5 cm³ (CI 95% [29.06-67.86])) compared to asymptomatic patients (7.4 cm³ (CI 95% [5.43-9.48])). Opening of the fourth ventricle was the most potent predictor of VTP (OR = 34.7, CI 95% [4.4-273.5], p = 0.001). In patients undergoing no additional treatment for pneumocephalus, ventricular air volume declined to an average of 41.7% of the initial postoperative volume on postoperative day 3.

CONCLUSIONS

Entrapment of intracranial and particularly ventricular air requiring emergent EVD occurred in 3.9% cases of intracranial surgery in the sitting position. Especially the opening of the fourth ventricle was associated with the development of VTP, which should warrant particularly diligent postoperative observation of these patients. In cases without neurological symptoms, the rate of spontaneous air resorption is sufficiently high to warrant expectant management.

Praying Sitting Position for Pineal Region Surgery: An Efficient Variant of a Classic Position in Neurosurgery

BACKGROUND

The sitting position has lost favor among neurosurgeons partly owing to assumptions of increased complications, such as venous air embolisms and hemodynamic disturbances. Moreover, the surgeon must assume a tiring posture. We describe our protocol for the "praying position" for pineal region surgery; this variant may reduce some of the risks of the sitting position, while providing a more ergonomic surgical position.

METHODS

A retrospective review of 56 pineal lesions operated on using the praying position between January 2008 and October 2015 was performed. The praying position is a steeper sitting position with the upper torso and the head bent forward and downward. The patient's head is tilted about 30° making the tentorium almost horizontal, thus providing a good viewing angle. G-suit trousers or elastic bandages around the lower extremities are always used.

RESULTS

Complete lesion removal was achieved in 52 cases; subtotal removal was achieved in 4. Venous air embolism associated with persistent hemodynamic changes was nonexistent in this series. When venous air embolism was suspected, an immediate reaction based on good teamwork was imperative. No cervical spine cord injury or peripheral nerve damage was reported. The microsurgical time was <45 minutes in most of the cases. Postoperative pneumocephalus was detected in all patients, but no case required surgical treatment.

CONCLUSIONS

A protocolized praying position that includes proper teamwork management may provide a simple, fast, and safe approach for proper placement of the patient for pineal region surgery.

Pneumocephalus-Induced Oculomotor Nerve Palsy After Atlanto-Occipital Decompression With Dural Plasty

BACKGROUND

Pneumocephalus after posterior fossa craniotomy is very common. However, cranial nerve dysfunction secondary to pneumocephalus is a very rare phenomenon.

PATIENT PRESENTATION

This case reports a patient who suffers from Chiari I malformation with syringomyelia in cervical spinal cord and develops unilateral oculomotor nerve palsy after atlanto-occipital decompression with dural plasty.

CONCLUSIONS

Cranial nerve dysfunction caused by pneumocephalus after craniotomy is rare and easily misdiagnosed. Timely head computed tomography or magnetic resonance imaging examination can exclude other causes and reveal the anatomic sites of pneumocephalus. Conservative treatment is available in most patients while sometimes it is necessary to drain the air.

Venous air embolism in the sitting position in cranial neurosurgery: incidence and severity according to the used monitoring

BACKGROUND

There is an ongoing debate about the sitting position (SP) in neurosurgical patients. The SP provides a number of advantages as well as severe complications such as commonly concerning venous air embolism (VAE). The best monitoring system for the detection of VAE is still controversial.

METHODS

In this retrospective analysis we compared 208 patients. Transesophageal echocardiography (TEE) or transthoracic Doppler (TTD) were used as monitoring devices to detect VAE; 101 cases were monitored with TEE and 107 with TTD.

RESULTS

The overall incidence of VAE was 23% (TTD: 10%; TEE: 37%), but the incidence of clinically relevant VAE (drop in end-tidal carbon dioxide above 3 mmHg) was higher in the TTD group (9 out of 17 VAE, 53%) compared to the TEE group (19 out of 62 VAE, 31%). None of the patients with recorded VAE had clinically significant sequelae.

CONCLUSIONS

In this small sample we found more VAE events in the TEE group, but the incidence of clinically relevant VAE was rare and comparable to other data. There is no consensus in the definition of clinically relevant VAE.

Carbon dioxide field flooding reduces the hemodynamic effects of venous air embolism occurring in the sitting position

PURPOSE

Although the utility of the sitting position is undisputed for biomechanical and ergonomic reasons, it has been debated in recent years for its risks, particularly venous air embolism (VAE). In order to reduce the hemodynamic effect of VAE, we changed the composition of the surgical field air partially replacing nitrogen with carbon dioxide (CO2) that better dissolves in human tissues.

METHODS

First, we tested our method on a test dummy in the sitting position. Infrared CO2 sensors were placed close to the wound opening and on the facial mask of the surgeon. An oxygen sensor was connected to a computer for data recording (ALTAIR(®), MSA Safety). This model showed that 10 L/min CO2 flow provides efficient air displacement, maintaining safety for the surgeon. We reproduced the above-described surgical field environment in ten consecutive cases of posterior fossa surgery performed in the sitting position. A homogeneous group of ten patients operated in the sitting position with standard setting environment was used for control. We intraoperatively monitored VAE with trans-esophageal echocardiography (TEE), end-tidal CO2 (ETCO2), CO2 arterial pressure (PaCO2), and hemodynamic changes.

RESULTS

Although the percentage of VAE was 70% in both groups, hemodynamic effects occurred in 10% of cases in the study group and in 40% of cases in the control group.

CONCLUSIONS

Our preliminary study shows that a CO2-enriched sitting position surgical microenvironment significantly reduces the hemodynamic effects of VAE, more likely because arterial CO2 emboli are more soluble and consequently much better tolerated than air emboli.

Normobaric hyperoxia for treatment of pneumocephalus after posterior fossa surgery in the semisitting position: a prospective randomized controlled trial

Background

Supratentorial pneumocephalus after posterior fossa surgery in the semisitting position may lead to decreased alertness and other symptoms. We here aimed to prove the efficacy of normobaric hyperoxia on the absorption of postoperative pneumocephalus according to a standardized treatment protocol.

Methods and Findings

We enrolled 44 patients with postoperative supratentorial pneumocephalus (> 30 ml) after posterior fossa surgery in a semisitting position. After randomisation procedure, patients received either normobaric hyperoxia at FiO₂ 100% over an endotracheal tube for 3 hours (treatment arm) or room air (control arm). Routine cranial CT scans were performed immediately (CT1) and 24 hours (CT2) after completion of surgery and were rated without knowledge of the therapy arm. Two co-primary endpoints were assessed: (i) mean change of pneumocephalus volume, and (ii) air resorption rate in 24 hours. Secondary endpoints were subjective alertness (Stanford Sleepiness Scale) postoperatively and attention (Stroop test), which were evaluated preoperatively and 24 hours after surgery. The mean change in pneumocephalus volume was higher in patients in the treatment arm as compared to patients in the control arm (p = 0.001). The air resorption rate was higher in patients in the treatment arm as compared to patients in the control arm (p = 0.0015). Differences were more pronounced in patients aged 52 years and older. No difference between patients in treatment arm and control arm was observed for the Stroop test. The distribution of scores in the Stanford Sleepiness Scale differed in the treatment arm as compared to the control arm, and there was a difference in mean values (p = 0.015).

Conclusions

Administration of normobaric hyperoxia at FiO₂ 100% via an endotracheal tube for 3 hours is safe and efficacious in the treatment of pneumocephalus after posterior fossa surgery in the semisitting position. Largest benefit was found in elderly patients and particularly in older men.

Trial Registration

German Clinical Trials Register DRKS00006273

[Near infrared spectroscopy (NIRS) in a neurocritical patient with an air embolisism and pneumocephalus]

The pneumocephalus is commonly encountered after neurosurgical procedures. The collections are usually small with benign behavior, and they respond to a conservative therapy. However, there is a high percentage of cases that may behave like a space-occupying lesion. A high index of suspicion is necessary to make the diagnosis and prompt treatment of these cases. Monitoring Near infra-red spectrometry (NIRS) monitoring could help to complete the diagnosis and treatment in these cases. A venous air embolism is a common complication in neurosurgical procedures that are performed in a sitting position, where this monitoring has also been shown to be useful. In the case presented, NIRS monitoring, along with clinical and analytical data, was used for the diagnosis of the two complications.

[Controversies in neuroanaesthesia: positioning in neurosurgery]

Positioning of the neurosurgical patient has several features such as the existence of specific positions (i.e: sitting, prone hyperlordotic, crouching ou kneeling positions) or the range of facilities for the same surgical indications. The last point, a source of controversy, is the subject of this review. Current indications for the sitting position, positioning for lumbar spine surgery and prevention of eye injuries are successively addressed.

Spontaneous intraparenchymal otogenic pneumocephalus: A case report and review of literature

Background:

Pneumocephalus is commonly associated with head and facial trauma, ear infection, or surgical interventions. Spontaneous pneumocephalus caused by a primary defect at the temporal bone level without association with pathological conditions is very rare. Few cases have been published with purely intraparenchymal involvement. We describe a rare case of spontaneous pneumocephalus arising from the mastoid cells with intraparenchymal location and present an extensive review of the existing literature.

Case Description:

A 57-year-old woman presented a brief episode of sudden otalgia in her left ear that was followed by a motor aphasia. Imaging revealed a left temporal intraparenchymal pneumocephalus in a close relationship with a highly pneumatized temporal bone. Left temporal craniotomy and decompression were performed. Further subtemporal exploration confirmed a dural defect and other osseous defects in the tegmen tympani, which were both consequently closed watertight.

Conclusion:

Although extremely rare, a spontaneous intraparenchymal pneumocephalus with mastoidal origin should be considered as a possible diagnosis in patients with suggestive otological symptoms and other non-specific neurological manifestations. Surgery is indicated to repair bone and dural defects.

[Questionnaire on the anaesthesiology treatment of patients subjected to posterior fossa neurosurgery]

OBJECTIVES

To find out, by means of a questionnaire, the procedures used by Spanish anaesthetists in peri-operative management of patients subjected to neurosurgery of the posterior cranial fossa.

MATERIAL AND METHODS

A closed-question type questionnaire was sent to Anaesthesiology Departments with a Neurosurgery Department on the participation of anaesthetists in the peri-operative treatment of patients subjected posterior fossa surgery.

RESULTS

The questionnaire was completed by 42 (57.5%) of the 73 national public hospitals with a Neurosurgery Department. The posterior fossa surgery was performed in the sitting position in 36 hospitals, although it was less frequently used than the lateral decubitus or prone decubitus position. There was little specific neurological monitoring, as well as little use of precordial and/or transcranial Doppler for detecting vascular air embolism. Nitrous oxide was used in less than 10% of the centres, and 15% avoided neuromuscular block when neurophysiological monitoring was used during the surgery. Cardiovascular problems were mentioned as being the most frequent in 29% of the centres, while in the post-operative period the most common complications were, cranial nerve déficit, airway oedema (23%), and post-operative vomiting (47%).

CONCLUSIONS

The results obtained from the questionnaire showed that the sitting position was less used than the prone position in posterior fossa surgery, and that neurophysiological monitoring is during surgery is hardly used.

Spontaneous otogenic pneumocephalus presenting with occipital subcutaneous emphysema as primary symptom: could tension gas cause the destruction of cranial bones?

The authors report, to the best of their knowledge, the first case of a spontaneous tension pneumocephalus with subcutaneous emphysema. Hyperpneumatization of the cranium and mechanical compression contributed jointly to the formation of a fistula, and air pressure caused a subsequent disruption of the suture and air leakage into the subcutaneous space. A minimally invasive otological procedure proved efficacious for resolution.

The impact of subdural air collection on intraoperative motor and somatosensory evoked potentials: fact or myth?

BACKGROUND

Surgery in the semi-sitting position is susceptible to changes in motor (MEP) and somatosensory evoked potentials (SEPs), which are not related to neurological impairment. These changes have been suggested to be caused by the insulating effect of subdural air collection. This study sought to investigate the correlation of MEP and SEP final-to-baseline amplitude ratios to postoperative volumetry of frontoparietal subdural air collection.

METHODS

Median nerve SEP and hand MEP findings of 47 patients operated on in the semi-sitting position were compared with 7 patients operated on in the supine position. Computed tomography was routinely performed on the 1st postoperative day in all patients, and subdural air volumetry was calculated. Final-to-baseline MEP and SEP amplitude ratios were calculated and correlated to subdural air volumetry.

FINDINGS

SEP changed in 12 patients, and MEP changed in 7 patients. Postoperative subdural air collections were significantly different between the groups (semi-sitting group, mean 31.2 cm(3); supine group, mean 2 cm3; p = 0.000). For the SEP ratios, a moderate negative correlation with subdural volumetry was found in the semi-sitting group (p = 0.044). Conversely, there was no correlation in the subset of patients with SEP attenuation (p = 0.846). As concerns the MEP ratios, no correlation was demonstrated in any group (semi-sitting, p = 0.967; supine, p = 0.193).

CONCLUSIONS

Although SEP amplitude reductions were associated with large subdural air collections, this was not observed in the subset of patients with SEP attenuation and for the MEP monitoring, suggesting other pathophysiological mechanisms, such as brain shift, for the artificial amplitude reduction.

Head computed tomography interpretation in trauma: a primer

Noncontrast computed tomography (CT) provides important diagnostic information for patients with traumatic brain injury. A systematic approach to image interpretation optimizes detection of pathologic air, fractures, hemorrhagic lesions, brain parenchymal injury, and abnormal cerebrospinal fluid spaces. Bone and brain windows should be reviewed to enhance injury detection. Findings of midline shift and mass effect should be noted as well as findings of increased intracranial pressure such as hydrocephalus and cerebral edema, because these may immediately influence management. Compared with CT, magnetic resonance imaging may provide more sensitive detection of diffuse axonal injury but has no proven improvement in clinical outcomes. This article discusses key CT interpretation skills and reviews important traumatic brain injuries that can be discerned on head CT. It focuses on imaging findings that may deserve immediate surgical intervention. In addition, the article reviews the limits of noncontrast CT and discusses some advanced imaging modalities that may reveal subtle injury patterns not seen with CT scan.