EDUCATION EXHIBIT Failed Endoscopic Sinus Surgery: Spec ... Introduction Sinusitis is a common...

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  • 177EDUCATION EXHIBIT

    Benjamin Y. Huang, MD • Kristen M. Lloyd, MD • John M. DelGaudio, MD • Eric Jablonowski, AS • Patricia A. Hudgins, MD

    Since its introduction over 2 decades ago, functional endoscopic si- nus surgery (FESS) has revolutionized the surgical management of chronic sinusitis. Performed over 200,000 times annually in the United States to treat medically refractory sinusitis, FESS has success rates as high as 98%. When surgical failure occurs, it is typically due to postoperative scarring or unaddressed outflow tract obstruction in the region of the frontal recess. The most common causes of surgical fail- ure in the frontal recess include remnant frontal recess cells, a retained uncinate process, middle turbinate lateralization, osteoneogenesis, scarring or inflammatory mucosal thickening, and recurrent polyposis. Computed tomography (CT) of the paranasal sinuses has become in- dispensable in evaluation of patients with FESS failure, particularly in the frontal recess, a location that can be difficult to visualize at endos- copy. Familiarity with the complex anatomy of the frontal recess and knowledge of the most common causes of surgical failure are essential for proper interpretation of sinus CT images obtained in patients be- ing considered for revision FESS of the frontal sinus. ©RSNA, 2009 • radiographics.rsnajnls.org

    Failed Endoscopic Sinus Surgery: Spec- trum of CT Findings in the Frontal Recess1

    ONlINE-ONly CME

    See www.rsna .org/education /rg_cme.html

    lEARNING OBJECTIVES After reading this article and taking the test, the reader

    will be able to:

    Discuss the anat- ■ omy of the frontal recess and the types of accessory frontal recess cells that may contribute to frontal recess stenosis.

    Describe com- ■ monly performed endoscopic proce- dures used to treat frontal sinusitis and their postoperative CT appearances.

    List common CT ■ findings associated with failed endo- scopic sinus surgery in the frontal recess.

    Abbreviation: FESS = functional endoscopic sinus surgery

    RadioGraphics 2009; 29:177–195 • Published online 10.1148/rg.291085118 • Content Codes: 1From the Department of Radiology, University of North Carolina School of Medicine, 101 Manning Dr, CB 7510, Chapel Hill, NC 27599-7510 (B.Y.H.); and the Departments of Radiology (K.M.L., E.J., P.A.H.) and Otolaryngology (J.M.D., P.A.H.), Emory University School of Medicine, At- lanta, Ga. Presented as an education exhibit at the 2007 RSNA Annual Meeting. Received May 2, 2008; revision requested June 2 and received July 30; accepted August 1. P.A.H. is a shareholder in Amirsys; all other authors have no financial relationships to disclose. Address correspondence to B.Y.H. (e-mail: bhuang@unch.unc.edu).

    ©RSNA, 2009

    See last page

    TEACHING POINTS

    Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at www.rsna.org/rsnarights.

  • 178 January-February 2009 radiographics.rsnajnls.org

    Introduction Sinusitis is a common medical problem in the United States, affecting 14%–16% of adults and accounting for approximately 11.6 million office-based outpatient visits annually (1,2). The current mainstay of treatment for sinusitis con- tinues to be medical therapy, and the majority of patients diagnosed with sinusitis respond ade- quately to a combination of antibiotics, deconges- tants, mucolytics, and steroids (3). However, in a significant proportion of patients with sinusitis, medical management alone is insufficient to re- lieve symptoms, necessitating referrals to rhinolo- gists for consideration of surgical management.

    First described over 2 decades ago (4), func- tional endoscopic sinus surgery (FESS) has be- come the treatment of choice for patients with medically refractory rhinosinusitis. FESS pro- cedures are now performed more than 200,000 times per year in the United States (5), with published success rates of 76%–98% for primary FESS and 65%–78% for revision cases (6). Al- though the majority of patients who undergo FESS for chronic sinusitis experience significant symptomatic relief, up to 23% of patients ulti- mately require revision surgery for continued or recurrent sinus symptoms after initial surgery (7,8).

    In patients presenting with sinusitis after FESS, the frontal sinus outflow tract is the re- gion where disease recurrence is most likely to occur (9). In addition, most medically refractory disease of the frontal sinuses can be attributed to obstruction at the level of the frontal recess (10). The frontal recess is a notoriously difficult area to treat with endoscopy owing to its anterior location and its tight confines between the orbit and anterior skull base. Furthermore, the frontal recess has a significant predilection for stenosis after FESS (11). The prevalence of frontal si- nusitis after FESS has not been established, but published series have reported persistent frontal sinusitis symptoms at short-term follow-up in 2%–11% of post-FESS patients (12) and long- term failure rates of 15%–20% (11), with up to 11% of these patients ultimately requiring revi- sion surgery (12,13).

    Frontal sinusitis after FESS can pose a num- ber of challenges to the sinus surgeon, not the least of which is elucidating the cause of surgical

    failure. Evaluation of patients in whom FESS has failed typically includes computed tomog- raphy (CT) of the paranasal sinuses to identify potential causes of sinus outflow tract stenosis. Radiologists tasked with interpreting these scans need to be familiar with the complex anatomy of the frontal recess and the processes that may contribute to surgical failure in order to generate accurate and meaningful reports for the referring rhinologists.

    The goal of this article is to review several of the most salient issues related to CT evaluation of patients with recurrent frontal sinus disease after FESS. Specific topics discussed include scanning technique, with a focus on the utility of multiplanar reformation; anatomy of the frontal recess and its many variants, including frontal re- cess cells; common endoscopic procedures used to treat disease in the frontal sinus and frontal re- cess; and common entities contributing to failure of FESS.

    CT Technique Timing is critical when imaging patients with chronic sinusitis. The presence of mucosal thick- ening is a nonspecific finding and can be seen in 90% of individuals in the presence of simple viral upper respiratory tract infections. Furthermore, changes due to simple cases of acute maxillary sinusitis may be evident for 4–6 weeks. Therefore, CT of the paranasal sinuses should not be per- formed until 4–6 weeks after initiation of medical therapy, and scanning should be delayed in pa- tients with acute upper respiratory infections (9).

    Before the widespread availability of spiral and, more recently, multidetector CT, direct coronal scanning was preferred because the coronal plane best demonstrates the anterior os- tiomeatal unit and skull base and has traditionally been thought to replicate most closely the actual view of the endoscopist. Recently, direct coronal scanning has fallen out of favor because modern multidetector CT scanners are capable of acquir- ing sections only a few tenths of a millimeter in thickness, allowing data to be acquired axially and then reconstructed with exquisite detail in any plane. Advantages of axial scanning include improved patient comfort during scanning and avoidance of artifacts created by dental restora- tions (which frequently plague scans acquired coronally). Furthermore, raw data from thin-sec- tion axial scanning are now commonly used for intraoperative stereotactic guidance systems.

    Teaching Point

  • RG ■ Volume 29 • Number 1 Huang et al 179

    The use of multiplanar reformation (sagittal and coronal) has been shown to improve pre- operative understanding of the frontal recess. Specifically, review of sagittal images significantly improves one’s ability to identify and measure the frontal recess (14) and is critical in assessment of obstructing anterior ethmoid cells (14,15). Kew et al (14) found that preoperative review of both sagittal and coronal reformatted images together significantly altered surgical planning in over one-half of cases when compared with review of coronal scans alone.

    We advocate thin-collimation contiguous heli- cal scanning with a maximum section thickness of no greater than 1 mm. Scans should be recon- structed in the axial, coronal, and sagittal planes by using both soft-tissue and high-resolution- algorithm bone windows with a reconstruction thickness of 3 mm or less. If available, transfer of raw data to a workstation is also extremely beneficial because it allows end users to further adjust parameters such as image brightness, con- trast, section thickness, and section plane, which can be particularly useful for teasing out complex bony anatomy.

    Anatomy of the Frontal Recess and Common Variants

    Familiarity with the complex and highly vari- able anatomy of the frontal recess is critical to its evaluation at CT. Along with the regions of the ethmoid infundibulum–middle meatus and the

    sphenoethmoidal recess, the frontal recess rep- resents one of the three anatomic “tight spots” that are implicated as sites of obstruction leading to sinusitis. At its most basic level, the frontal recess can be conceptualized as an inverted fun- nel within the anterior ethmoid complex through which the frontal sinus drains. The tip or ap