Four-cut sinus computed tomographic scanning in screening for sinus disease.

Objective: We sought to calculate the sensitivity, specificity, negative predictive value, and positive predictive value of a limited sinus computed tomographic (CT) scan for sinus disease.

Methods: We conducted a retrospective case series. Inclusion criteria included a sinus CT scan obtained between April 1999 and November 2000. From the complete sinus CT scan, the limited series were obtained by blocking from view all the other cuts and leaving the radiologist only four slices to read (midfrontal, anterior maxillary sinuses, posterior maxillary sinuses, and midsphenoidal). The complete CT scan was the "gold standard."

Results: Fifty-one patients were eligible. We observed 81.3% sensitivity, 89.5% specificity, a 73.9% negative predictive value, and a 92.9% positive predictive value for the limited CT scan for the detection of sinus disease. This sensitivity and specificity were higher than reported in the literature for plain films.

Conclusion: The limited sinus CT scan is superior to plain radiographs but is not as good as the full CT scan in the evaluation of sinusitis.

Key Words: four-cut computed tomography, sensitivity, sinus disease, specificity

**********

Sinusitis is a common disease; its prevalence is approximately 50 million in the United States. (1) Plain radiographic films are frequently used in clinical practice for the evaluation of nasal and paranasal sinus disease even though this radiologic examination lacks accuracy. (2) A sinus computed tomographic (CT) scan has been shown to be superior to radiographs in evaluating paranasal sinuses. (2) McAlister et al (3) compared plain radiographs and CT scans in 70 infants and children with recurrent sinusitis. In their study, a discrepancy was seen in 74% of patients; 46% of patients with a normal radiographic result had abnormal findings on the CT scan, and 34% of patients with an abnormal radiograph had normal findings on the CT scan. Burke et al (4) studied 30 adult patients comparing sinus radiographs with CT scans in acute sinusitis. They found that radiographs had a sensitivity of 48 to 67% and a specificity of 75 to 100% depending on the reader.

Complete sinus CT scan is considered the "gold standard" for evaluating paranasal sinus disease. However, this modality is expensive and exposes the patient to a high dose of radiation, especially for the radiosensitive orbital lens. (5) A four-cut miniseries sinus CT scan could be a reasonable alternative to both plain films and a complete sinus CT scan. A four-cut CT scan uses 80% less radiation than a complete CT scan, (5) and it is cheaper than a CT scan. Wippold et al (6) studied 25 adult patients with clinical history and findings suggestive of sinusitis (200 sinus compartments total, 8 for each patient); the limited CT scan agreed with the complete CT scan in 82% of the 200 sinus compartments studied. Goodman et al (7) studied 44 patients and found that the sensitivity and specificity of limited sinus CT scans are 93.3 and 89.3%, respectively.

The primary objective of this study was to calculate the sensitivity, specificity, negative predictive value, and positive predictive value of a four-cut sinus CT scan, with the gold standard being the complete sinus CT scan. Depending on the sensitivity and specificity of the miniseries CT scan compared with the complete CT scan and the reported values for plain radiographs, the miniseries could be the initial test of choice for workup of clinically suspected sinusitis.

Methods

We conducted a retrospective case series. TriHealth Institutional Review Board approval was obtained before data collection. Inclusion criteria included a sinus CT scan obtained at Good Samaritan Hospital in Cincinnati, OH, between April 1999 and November 2000. All CT scans during the study period were obtained with a third-generation scanner, Siemens type, Somatom plus Spiral (24 s) or Somatom plus Spiral (40 s) (Siemens AG, Munich, Germany). On the CT scanner table, the patient assumed a supine position with his or her neck extended. Contiguous noncontrast coronal 2-mm slices were obtained extending from the anterior frontal sinuses to 2 cm posterior to the posterior wall of the frontal sinuses; in addition, contiguous 5-mm slices to the posterior wall of the sphenoid sinus were performed. All slices were parallel and formed a 90-degree angle with a plane passing through the hard palate.

For each patient, we produced a four-cut miniseries sinus CT scan from the original complete sinus CT scan. The four cuts that were selected included one cut through the midfrontal sinuses, one cut through the anterior maxillary sinuses (showing anterior ethmoid also), one cut through the posterior maxillary sinuses (shows posterior ethmoid also), and a fourth cut at the midsphenoid level. The radiologist that read the original sinus CT scan during the inclusion period was then asked to read the miniseries CT. All other views were blocked from the radiologist. The time period between the radiologist reading the complete CT scan and the miniseries CT scan was at least 12 months and as long as 30 months. For each of the seven sinuses on the miniseries CT scan (right frontal, left frontal, right ethmoidal, left ethmoidal, right maxillary, left maxillary, and sphenoid), the radiologist was asked to read the findings as either normal, mild mucosal thickening, moderate/severe mucosal thickening, air fluid level, or complete opacification. This has been the standard terminology for grading sinus CT scan findings at this institution for several years. The radiologist was also asked to give an overall impression of the miniseries as normal or abnormal.

The radiologist did not have information regarding the patient's symptoms and had no access to the previous complete sinus CT scan reading. The primary investigator then collected data from the original complete CT scan report. Results from each of the seven sinuses were recorded using the same standard terminology (normal, mild mucosal thickening, moderate/severe mucosal thickening, air fluid level, or complete opacification). An overall impression of normal versus abnormal for the complete CT scan was also recorded. The original interpretation of the complete sinus CT scan was considered the gold standard.

We then compared the results of the miniseries CT scan to the complete CT scan. We calculated the sensitivity, specificity, negative predictive value, and positive predictive for each sinus separately and for the overall miniseries CT scan. Data analysis was conducted using BMDP New System (Statistical Solutions, Saugus, MA) statistical software.

Results

There were 90 patients who met the inclusion criteria. Thirty-five of the patients' CT scans were off-site from the hospital and unavailable. Four patients were excluded because the radiologist that read the original CT scan was no longer with the institution. The remaining 51 patients were eligible for the study. The study population had an average age of 40.7 years (range, 11-70 yr). There were 35 female patients (average age, 37.4 yr) and 16 male patients (average age, 47.9 yr). The sensitivity, specificity, negative predictive value, and positive predictive value for each of the seven sinuses and the overall reading of the miniseries CT scan are reported in Table 1. Considering each sinus separately, the lowest sensitivities were for the left maxillary sinus and right ethmoidal sinus (48 and 50%, respectively); the lowest specificities were for the ethmoidal sinuses (78 and 84%, respectively), whereas the specificity of all other sinuses was above 90%.

Discussion

Sinusitis is a common problem encountered by family practitioners and internists in the outpatient setting. By Kern's (8) definition, acute sinusitis is an infection in a paranasal sinus lasting less than 3 weeks, whereas subacute sinusitis is an infection lasting from 3 weeks to 3 months.

The four-cut sinus CT scan or miniseries is a widely available CT scan of the sinuses that could be obtained from any CT scan machine. The only difference with the full CT scan is the fewer number of cuts (four slices instead of an average of 25 slices).

The signs and symptoms of acute and chronic sinusitis can be nonspecific, and imaging tests are sometimes ordered to help the clinician make a diagnosis. Plain films are commonly used to confirm or rule out sinusitis even though many studies have shown their low sensitivity and specificity. (2-4) The reported sensitivity and specificity of plain films based on a meta-analysis was 54 and 64%, respectively. (7) The miniseries CT scan is an alternative to plain films in the evaluation of paranasal sinus disease. Our data show that four-cut sinus CT scanning is a better test compared with plain films because of its higher sensitivity and specificity (81% and 89%). The specificity for our miniseries CT scan was similar to the results found by Goodman et al, (7) but the sensitivity in our study was lower. Their study showed overall sensitivity of 93.3% and specificity of 89.3% for a four-cut miniseries CT scan using the same gold standard.

From the clinician's perspective, a suspicion of sinusitis is frequently treated symptomatically or empirically with antibiotics, but sometimes the clinician opts for imaging tests; in that case, our results suggest that the miniseries CT is a good test to rule in disease because of its high specificity and positive predictive value but a less valuable test to rule out disease because of the lower sensitivity and negative predictive value.

This study has several limitations that need to be contemplated when considering our results. First, the study was performed in a single institution. Second, to eliminate an interreader variability, we asked the same radiologist who read the original CT scan to read the miniseries. Even though there was at least 12 months between the two readings, some recall bias may have occurred. Finally, in our institution, we routinely provide the radiologist with clinical information about the patient, which was not done for the reading of the miniseries. This difference could have led to different interpretations of the scanned images.

Future research could include other imaging modalities, especially magnetic resonance imaging; in particular, a limited series magnetic resonance imaging scan in diagnosing sinus disease could offer the advantage of no radiation and more accurate imaging of soft tissues. A larger, prospective study comparing complete and miniseries CT scanning for sinus disease should be conducted to better calculate the specificity and sensitivity of this diagnostic test. If repeat studies indicate that the sensitivity is similar to our results (81%), most clinicians would likely opt for the gold standard, especially when ruling out disease is clinically important.

Conclusion

The four-cut sinus CT scan is superior to plain radiographs but is not as good as the gold standard, full CT scan, in the evaluation of sinusitis, especially for ruling out disease. Although neither one is optimal, given similar cost, the four-cut sinus CT scan is recommended over plain films because of its higher sensitivity and specificity.

Table 1. Results (a)

Gold Standard                  Test Assay       TP  TN  FP  FN

Complete right frontal    Mini right frontal     6  42  1    2
Complete left frontal     Mini left frontal      4  42  2    3
Complete right ethmoidal  Mini right ethmoidal   9  26  7    9
Complete left ethmoidal   Mini left ethmoidal    7  33  6    5
Complete right maxillary  Mini right maxillary  12  31  2    6
Complete left maxillary   Mini left maxillary   12  24  2   13
Complete sphenoidal       Minisphenoidal         6  40  2    3
Complete overall          Miniseries overall    26  17  2    6

Gold Standard          Sensitivity     Specificity   PPV    NPV

Complete right frontal    75              97.67     85.71  95.45
Complete left frontal     57.14           95.45     66.67  93.33
Complete right ethmoidal  50              78.79     56.25  74.29
Complete left ethmoidal   58.33           84.62     53.85  86.84
Complete right maxillary  66.67           93.94     85.71  83.78
Complete left maxillary   48              92.31     85.71  64.86
Complete sphenoidal       66.67           95.24     75     93.02
Complete overall          81.25           89.47     92.86  73.91

(a) TP, true positive; TN, true negative; FP, false positive; FN, false
negative; PPV, positive predictive value; NPV, negative predictive
value.

Acknowledgments

We acknowledge the following radiologists for their expertise and assistance with the project: Dr. Charles T. McConnell, Dr. Elizabeth S. Alexander, Dr. James M. Meranus, Dr. Francis J. Schlueter, Dr. Roger Vithalani, and Dr. David Huelsman.

From the Departments of Internal Medicine and Radiology, Good Samaritan Hospital; the Department of Epidemiology, Bethesda Family Medicine Residency Program; and the E. Kenneth Hatton, MD, Institute for Research and Education, Cincinnati, OH.

We received no financial support for this project.

Reprint requests to Scott E. Woods, MD, MPH, MEd, Bethesda Family Medicine Residency Program, 4411 Montgomery Road, Suite 200, Cincinnati, OH 45212. Email: [e-mail]

Accepted June 25, 2003.

Copyright [C] 2004 by The Southern Medical Association 0038-4348/04/9701-0018

References

(1.) Witte RJ, Heurter JV, Orton DF, et al. Limited axial CT of the paranasal sinuses in screening for sinusitis. AJR Am J Roentgenol 1996;167:1313-1315.

(2.) Davidson TM, Brahme FJ, Gallagher ME. Radiographic evaluation for nasal dysfunction: Computed tomography versus plain films. Head Neck 1989;11:405-409.

(3.) McAlister WH, Lusk R, Muntz HR. Comparison of plain radiographs and coronal CT scans in infants and children with recurrent sinusitis. AJR Am J Roentgenol 1989;153:1259-1264.

(4.) Burke TF, Guertler AT, Timmons JH. Comparison of sinus x-rays with computed tomography scans in acute sinusitis. Acad Emerg Med 1994;1:235-239.

(5.) Gross GW, McGeady SJ, Kerut T, et al. Limited-slice CT in the evaluation of paranasal sinus disease in children. AJR Am J Roentgenol 1991;156:367-369.

(6.) Wippold FJ II, Levitt RG, Evens RG, et al. Limited coronal CT: An alternative screening examination for sinonasal inflammatory disease. Allergy Proc 1995;16:165-169.

(7.) Goodman GM, Martin DS, Klein J, et al. Comparison of a screening coronal CT versus a contiguous coronal CT for the evaluation of patients with presumptive sinusitis. Ann Allergy Asthma Immunol 1995;74:178-182.

(8.) Kern EB. Sinusitis. J Allergy Clin Immunol 1984;73:25-31.

RELATED ARTICLE: Key Points

* A miniseries computed tomographic (CT) scan has a sensitivity of 81% and a specificity of 89% for detecting sinus disease compared with a complete CT scan.

* Given similar cost, the four-cut sinus CT scan is the recommended diagnostic test over plain radiographs because of its higher sensitivity and specificity.

Jean-Pierre S. Awaida, MD, Scott E. Woods, MD, MPH, MED, Meg Doerzbacher, RN, MSN, Yury Gonzales, MD, and Timothy J. Miller, MD

Even if you are on the right track, you'll get run over if you just sit there.

--Will Rogers