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Correlation of CT and Intraoperative Findings With Pulmonary Data In Idiopathic Subglottic Stenosis

Tyler S Weaver, BS1; Shannon M Kraft, MD2; Bronwyn E Hamilton, MD,1; Joshua S Schindler, MD1

1Oregon Health & Science University, 2University of Kansas Medical Center

1. Brandenburg JH. Idiopathic Subglottic Stenosis. Trans Am Acad Ophthalmol Otolaryngol. 1972; 76(5):1402-6. 2. Mark EF, Meng F, Kradin RL. Idiopathic Tracheal Stenosis: A Clinicopathologic Study of 63 Cases and Comparison of the Pathology with Chondromalacia. Am J Surg Path 2008;32(8): 1138-1143. 3. Valdez TA and Shapsay SM. Idiopathic subglottic stenosis revisited. Ann Otol Rhinol Laryngol. 2008;111(8):690-5. 4. Koufman JA. The otolaryngologic manifestations of gastroesophageal reflux disease (GERD): a clinical investigation of 225 patients using ambulatory 24-hour pH monitoring and an experimental investigation of the role of acid and pepsin in the development of laryngeal injury. Laryngoscope. 1991;101(4 Pt 2 Suppl 53):1-78. 5. Blumin JH and Johnston N. Evidence of extraesophageal reflux in idiopathic subglottic stenosis. Laryngoscope. 2011;121(6):1266-73 6. Maldonado F, Loiselle A, DePew ZS, Edel ES, Ekbom DC, Malinchoc M, Hagen CE, Alon E and Kasperbauer JL. Idiopathic Subglottic Stenosis: An Evolving Therapeutic Algorithm. Laryngoscope 2013 (epub ahead of print) 7. Damrose EJ. On the development of idiopathic subglottic stenosis. Med Hypoth 2008;71:122-125. 8. Dumoulin E, Stather DR, Gelfand G, Maranda B, Maceachern P, Tremblay A. Idiopathic subglottic stenosis: a familial predisposition. Ann Thorac Surg. 2013 Mar;95(3):1084-6. 9. Naidlich DP and Haartkin TJ. Airway and lung: correlation of CT and fiberoptic bronchoscopy. Radiology 1995;197:1-12. 10. Gluecker T, Lang F, Bessler S, Monnier P, Meuli R, Schnyder P, Duvoisin B. 2D and 3D imaging correlated to rigid endoscopy in complex laryngo-tracheal stenosis. Eur Radiol. 2001;11:50-54. 11. Hyatt RE. Evaluation of major airway lesions using the flow volume loop. Ann Otol Rhinol Laryngol 1975; 84:635-642. 12. Nouraei SAR, Winterborne C, Nouraei M, et al. Quantifiying the physiology of Laryngotracheal stenosis: Changes in pulmonary dynamics in response to graded extrathoracic resistive loading. Laryngoscope. 2007; 117: 581-589. 13. Taha MS, Mostafa BE, Fahmy M, Ghaffar MK, Ghany EA. Spiral CT virtual bronchoscopy with multiplanar reformatting in the evaluation of post-intubation tracheal stenosis: comparison between endoscopic, radiological and surgical findings. Eur Arch Otorhinolaryngol. 2009;266:863-866. 14. Carretta A, Melloni G, Ciriaco P, Libretti L, Casiraghi M, Bandiera A, Zannini P. Preoperative assessment in patients with postintubation tracheal stenosis : Rigid and flexible bronchoscopy versus spiral CT scan with multiplanar reconstructions.Surg Endosc. 2006 Jun;20(6):905-8. 15. Miller RD and Hyatt RE. Obstructing lesions of the larynx and trachea: clinical and physiologic characteristics. Mayo Clin Proc 1969; 44(3): 145-161.

References

• To assess the accuracy of computed tomography (CT) measurements of idiopathic subglottic stenosis (iSGS)

• To evaluate for correlations between CT findings and pulmonary function tests (PFT)

Objective Patient Data

• From 2006-2012, 25 patients were newly diagnosed with iSGS • 15 obtained preoperative CT scans • 12 of the 15 patients obtained PFTs

• Median age 63 years (IQR 52-73) and body mass index (BMI) 30.5 (IQR 23.9-34.2).

Intraoperative vs CT Measurements • CT measured values for stenosis did not correlate with intraoperative

measurements (p=0.72, p=0.77, respectively) • CT underestimated the distance distance of the lesion from the true vocal folds

in 6/15 cases. • CT overestimated the length of the stenosis in 11/15 cases. PFTs and CT Measurements • Median cross sectional area of the patent airway was 65.7 mm2 (IQR 48.8-89.9

mm2), percent stenosis was 58.6% (IQR 49.9-69.7) • Spearman correlation test showed no correlation between RB measurements or

CT measurements with PFTs

• Sub-analysis of 4 patients with cross sectional area <50 mm2 also demonstrated no correlation between anatomic measures and PFT values.

Introduction

• Retrospective chart review at single academic institution • Exclusion criteria: History of airway surgery, airway trauma,

tracheotomy, positive c-ANCA or ACE level or intubation in last year

• All patients underwent standard microdirect laryngoscopy with bronchoscopy with measurement of stenosis

• Head & Neck Radiologist blinded to intraoperative measurements performed all radiographic measurements

• Descriptive data reported as median with Interquartile Range (IQR)

• Spearman’s Correlation test used to identify relationships between anatomic (RB and CT) data and physiologic (PFT) data

Methods and Materials

Intraoperative vs CT Measurements • Using RB as the presumptive gold standard

• CT measured distance below the cords = 81% accurate • CT measured length of stenosis = 58% accurate

• As a retrospective study, CT protocols were not standardized, only 1/3 of CTs used 1mm slices, which would affect accuracy of radiographic measures.

• CT cannot distinguish between stenosis and secretions, which may explain why CT measures of stenosis were overestimated.

• Alternatively, the lack of correlation between RB and CT may reflect inaccuracy attributable to the “gold standard.” • Previous studies looking at post-intubation subglottic

stenosis vary in their reports of RB and CT accuracy in subglottic involvement and length of stenosis when comparing each to resected stenosis specimens.13, 14

PFTs and CT Measurements • According to Poiseulle’s law, decreased cross-sectional area and

length of stenosis (to a lesser degree) should correlate with worsening PFT measures

• Unable to demonstrate relationship in this study, although we

have found certain parameters (FEV1/PEF, PEF, PIF, FIF50%) change in iSGS patients after dilations (unpublished observations)

• Is there no correlation, or is the issue with the inherent flaws in our ability to measure stenosis or changes in airflow?

• Computed Tomography: • Non-standardized protocols • Errors in measure due to thicker slices or narrowing not

attributable to stenosis • Pulmonary Function Tests

• Dependent on patient effort • May not be adequately sensitive to detect mild stenosis • Trachea must be narrowed to 8 mm (~ 80% stenosis) or 50

mm2 to create detectable changes of the flow15

• To account for this, we did a sub-analysis of patients with a stenosis with a cross-sectional area less than 50mm2, but the numbers were small (n=4) and no correlation could be demonstrated.

• Future Directions -- Computational Fluid Dynamics (CFD) • Navier-Stokes equations solve for pressure drops and flow

changes across stenosis using CT generated airway model • Will be of interest to see if correlate with physiologic tests for

flow like PFTs.

Discussion

• While we could not demonstrate a correlation between structural and functional data in this study, CT and PFTs both provide important supplemental information in the work-up of iSGS.

• Future studies should focus on standardizing protocols for both tests to increase both accuracy and sensitivity.

Conclusions

• iSGS first described in 1972 by Brandenburg1. • Non-specific inflammatory process—diagnosis of exclusion • Stenosis at level of cricoid and 1st and 2nd tracheal rings1 • Affects primarily females from 30-50 years old2

• Possible etiologies include estrogen,3 laryngopharyngeal reflux,4,5 seronegative polyangiitis with granulomatosis,6 trauma from chronic cough7 or heredity factors8.

• Work-up of iSGS frequently includes CT and PFT data prior to definitive rigid bronchoscopy (RB). • Computed Tomography (CT): • Well-tolerated • Can “see” past high grade stenosis to evaluate the distal

airway • Provides structural information as to the intraluminal and

extraluminal contributions to the obstruction9,10. • Pulmonary Function Tests: • Physiologic test that quantifies airflow • Hyatt’s classic description of the flow-volume loop can

describe level of obstruction (variable intra-thoracic, variable extra-thoracic and fixed)11

• Can assess both degree of stenosis and quantify the results of interventions12.

• RB is still considered the gold standard.

Results

Figure 1. Direct bronchoscopy view of iSGS.

Figure 2. Axial and sagittal CT view of iSGS.

Figure 3. Intraoperative vs CT measurements of stenosis.

FEV1 FVC

FEV1/

FVC PEF PIF

FEV1/

PEF

FIF

50%

AP Radius 0.72 0.59 0.79 0.68 0.26 0.11 0.41

Transverse Radius 0.50 0.78 0.28 0.98 0.38 0.57 0.59

Cross Sectional Area 0.90 0.85 0.65 0.64 0.16 0.18 0.32

% Stenosis 0.99 0.82 0.80 0.67 0.20 0.26 0.31

Figure 4. Poiseuille’s law. Q = flow, P = pressure, r = radius, η = viscosity, l = length

Median IQR

Distance Below TVC CT 13.6 mm 10.8-16.0

OR 14 mm 12-16

Length of Stenosis CT 18.1 mm 15.1-19.4

OR 10 mm 8.5-16.5

Cross-Sectional Area CT 65.7 mm2 48.8-89.8

OR NR NR

Percent Stenosis CT 58.6% 49.9-69.7

OR NR NR

Table 1. Intraoperative vs CT measures of stenosis.

Table 2. Correlation of CT measurements with PFT data (p value reported).