Xenon-Enhanced Dynamic Dual-Energy CT Is Able to Quantify Sinus Ventilation Using Laminar and Pulsating Air-/Gas Flow Before and After Surgery: A Pilot Study in a Cadaver Model

Background

Chronic rhinosinusitis is a common disease with a significant impact on the quality of life. Topical drug delivery to the paranasal sinuses is not efficient to prevent sinus surgery or expensive biologic treatment in a lot of cases as the affected mucosa is not reached. More efficient approaches for topical drug delivery are, therefore, necessary. In the current study, dual-energy CT (DECT) imaging was used to examine sinus ventilation before and after sinus surgery using a pulsating xenon gas ventilator in a cadaver head.

Methods

Xenon gas was administered to the nasal cavity of a cadaver head with a laminar flow of 7 L/min and with pulsating xenon-flow (45 Hz frequency, 25 mbar amplitude). Nasal cavity and paranasal sinuses were imaged by DECT. This procedure was repeated after functional endoscopic sinus surgery (FESS). Based on the enhancement levels in the different sinuses, regional xenon concentrations were calculated.

Results

Xenon-related enhancement could not be detected in most of the sinuses during laminar gas flow. By superimposing laminar flow with pulsation, DECT imaging revealed a xenon wash-in and wash-out in the sinuses. After FESS, xenon enhancement was immediately seen in all sinuses and reached higher concentrations than before surgery.

Conclusion

Xenon-enhanced DECT can be used to visualize and quantify sinus ventilation. Pulsating air-/gas flow was superior to laminar flow for the administration of xenon to the paranasal sinuses. FESS leads to successful ventilation of all paranasal sinuses.

Effects of Oxymetazoline on the Ventilation of Paranasal Sinuses in Healthy Subjects

Background

Impairment of sinus ostial function is considered an important factor in the pathophysiology of sinus disease. The use of the decongestants such as α2-agonists is thought to improve sinus ostial function. Previous studies have shown an effect of α2-agonists on maxillary sinus ostial function only when administered in nasal bellows, but not as a nasal spray or nasal drops. The effect of decongestants on ventilation of the frontal and posterior ethmoidal and sphenoidal sinuses has not been studied to date.

Methods

In this study, the 133-xenon washout method was used to determine ventilation for all paranasal sinuses before and after administration of oxymetazoline as nasal drops in eight subjects and from nasal bellows in nine healthy subjects.

Results

No significant effect of oxymetazoline on sinus ventilation was seen in either group.

Conclusions

The results indicate that α2-agonists do not have any effect on sinus ventilation in healthy subjects. However, one cannot exclude that decongestants improve sinus ventilation in patients suffering from sinus disease and this requires further studies.

Physical and computational modeling of ventilation of the maxillary sinus

Objective. Sinus ventilation is often associated with sinusitis, a common condition causing significant pain and reduced quality of life. Clinical implications of the diverse anatomy of ostia connecting sinus to nose and the efficacy of surgical intervention in chronic sinusitis are poorly understood. This study aimed to measure sinus ventilation and explore variables in physical and mathematical models.

Study Design. γ-Scintigraphy of krypton 81m (81mKr) was carried out in a stylized physical model of a human maxillary sinus. Computational simulations matched this model for validation and extrapolated to combinations of variables not possible experimentally for evaluation of transport mechanisms.

Setting. Research laboratory in Department of Aeronautics. Imperial College London, and Department of Nuclear Medicine, Hammersmith Hospital, London.

Methods. 81mKr distribution was measured with both single- and double-ostia sinuses. Computational simulations matched and extended the physical measurements and enabled separate identification and evaluation of transport mechanisms.

Results. The presence of an additional ostium resulted in a 50-fold increase in the effective volume flow rate of gas replacement in the sinus. In the case of a single ostium, doubling the ostial diameter doubled the effective volume flow rate of gas exchange.

Conclusion. γ-Scintigraphy of 81mKr enables quantitative assessment of effective volume flow rate in physical model sinuses. These flow rates obtained experimentally for single- and double-ostium sinuses match the computational predictions of matching geometries. The increased ventilation seen with an additional ostium or increased ostial diameters may not be clinically beneficial, because it could reduce nitric oxide concentration in the sinus.

The effect of maxillary sinus antrostomy size on xenon ventilation in the sheep model

OBJECTIVE

A major goal of maxillary antrostomy is to increase sinus ventilation. Limited data exist regarding the effect of maxillary antrostomy size on sinus ventilation. We sought to quantify the effect of uncinectomy, small antrostomy, and large antrostomy on maxillary sinus ventilation using xenon-enhanced CT in the sheep model. MATERIALS, STUDY DESIGN, AND METHODS: A xenon-oxygen-air mixture was delivered to 8 fresh cadaveric sheep heads while repeated CT scans were performed through the maxillary sinuses. Baseline and postoperative studies were performed after an endoscopic uncinectomy, small antrostomy, or large antrostomy was created. Images were analyzed to measure the density of the xenon gas in the maxillary sinus as a function of time, generating a time constant.

RESULTS

The time constants for both small antrostomy and large antrostomy were significantly different compared to baseline ( P = 0.003 for both). The time constant comparison between small antrostomy and large antrostomy was not significant ( P = 0.948).

CONCLUSIONS

A small antrostomy produces a statistically significant increase in maxillary sinus ventilation over baseline. No significant further ventilation increase is obtained by creating a large antrostomy in the sheep model. This lends credence to the use of small antrostomies to improve maxillary sinus ventilation in human sinus surgery.