Diagnostic Tools for Sinonasal Disease and Role of Office Imaging
Luke Rudmik
Timothy L. Smith
Due to the breadth of sinonasal pathologies, several diagnostic tools are available during rhinologic evaluation. Diagnostic evaluation always begins with a thorough history and physical exam. The importance of a complete history and physical cannot be over emphasized, as it narrows the differential diagnosis and focuses subsequent diagnostic tests. An incomplete history and exam may result in needless investigations and, worst-case scenario, lead to a misdiagnosis with a delay in treatment. A formal discussion on the rhinologic history and physical exam is beyond the scope of this chapter but should be performed on all patients. This chapter discusses the various rhinologic investigations used to evaluate patients with sinonasal pathology.
RIGID SINONASAL ENDOSCOPY
Rigid sinonasal endoscopy remains one of the most useful diagnostic tools used during the evaluation of sinonasal disease. Recent advancements in endoscopic technology have provided high-definition image detail with improved magnification. Most otolaryngologists will perform inoffice rigid sinonasal endoscopy using a 4 mm 30-degree endoscope; however, a smaller 2.7 mm diameter endoscope and 0, 45, and 70-degree scopes are available, depending on surgeon preference. Utilizing a rigid, rather than flexible, endoscope enables the physician to scope with one hand and perform procedures, such as suctioning or debriding, with the other hand.
To improve patient comfort and optimize visualization, the procedure often begins with the application of a topical anesthetic and decongestant. Application can be achieved with either cotton pledgets or nebulized spray and commonly involves a mixture of 4% Xylocaine and xylometazoline.
A systematic approach to the endoscopic exam will provide a thorough evaluation and minimize missed information. A common approach to rigid sinonasal endoscopy involves a three-pass technique (Table 28.1). The first pass involves passing the scope medial to the inferior turbinate, along the floor of nose. Structures visualized include the inferior turbinate, inferior portion of the middle turbinate, nasopharynx, and eustachian tube. The second pass places the scope medial to the middle turbinate to visualize the sphenoethmoidal recess. The relationship of the septum to the middle turbinate may impair this step. A classification by Schaitkin et al. (1) describes the endoscopic turbinoseptal (TS) relationship following nasal decongesting: TS1—medial and lateral aspect of middle turbinate is visualized; TS2—anterior attachment of middle turbinate partially obscured by septum; TS3—anterior attachment of middle turbinate completely obscured by septum; and TS4—septum contacting the lateral nasal wall (Fig. 28.1). Patients with TS2, 3, and 4 often require a septoplasty for access during endoscopic sinus surgery (ESS). The third pass visualizes lateral to the middle turbinate, within the middle meatus. Anatomic abnormalities such as choncha bullosa and accessory fontanelles can be visualized. Noting the presence of the mucosal inflammation, mucopurulence, mucus recirculation, crusting, masses, or polyps are important information, which can guide the ordering of subsequent diagnostic tests (Fig. 28.2).
A thorough and complete endoscopic exam is critical in the evaluation of a patient with sinonasal disease. The objective information provided can improve diagnosis, guide therapy, and monitor therapeutic response during follow-up. A systematic approach, as mentioned above, can improve diagnostic yield and consistency.
RADIOLOGIC INVESTIGATIONS
Radiographic imaging of the paranasal sinuses has evolved over the last century. Early options were limited to plain films (roentgenographs), which were fraught with inaccuracy and provided minimal diagnostic yield. Several
technologic innovations over the last 15 to 20 years have given otolaryngologists several new imaging modalities, which have subsequently advanced our understanding of sinonasal disease and improved patient care. Current options primarily include high-resolution computed tomography (CT) and magnetic resonance imaging (MRI). Although the majority of sinonasal pathology can be diagnosed with a thorough history, physical exam, and rigid sinonasal endoscopy, radiographic imaging has become a standard adjunct in the workup of sinonasal disease. The primary role of radiologic imaging is to improve the diagnosis, define extent of regional disease, and aid in surgical planning.
technologic innovations over the last 15 to 20 years have given otolaryngologists several new imaging modalities, which have subsequently advanced our understanding of sinonasal disease and improved patient care. Current options primarily include high-resolution computed tomography (CT) and magnetic resonance imaging (MRI). Although the majority of sinonasal pathology can be diagnosed with a thorough history, physical exam, and rigid sinonasal endoscopy, radiographic imaging has become a standard adjunct in the workup of sinonasal disease. The primary role of radiologic imaging is to improve the diagnosis, define extent of regional disease, and aid in surgical planning.
TABLE 28.1 RIGID SINONASAL ENDOSCOPY 3-PASS TECHNIQUE | ||||||||
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 Figure 28.1 Endoscopic appearance of various septal deviations. A: TS1 view, (B) TS2 view, (C) TS3 view. |
Plain Films (Roentgenographs)
Plain films have been the traditional sinus imaging modality; however, they have been made obsolete with the emergence of CT and MRI. The four most common sinus plain film views include: Waters’, Caldwell, Lateral, and Submentovertex. The radiation exposure from these four views is 40 to 60 mSv (2). Although limited, these views were able to assess the size and opacification of the sinuses, as well as identify septal deviations (3).
The major limitations of plain films are their inability to provide accurate diagnostic information pertaining to the status of the ostiomeatal complex (OMC), surrounding soft tissue, and anatomic variations of the sinuses. Although demonstration of an air-fluid level may be helpful during the workup of acute rhinosinusitis, several studies have demonstrated limited accuracy rates (70% and 75%) (4,5)
when compared to a CT scan. With the advent of ESS, detailed preoperative anatomic assessment is necessary to optimize surgical dissection and minimize complications. Due to significant tissue and bony overlap, plain films cannot provide detailed anatomic information. Currently, the only indication for plain films of the sinuses is the inability to obtain other imaging modalities such as CT or MRI.
when compared to a CT scan. With the advent of ESS, detailed preoperative anatomic assessment is necessary to optimize surgical dissection and minimize complications. Due to significant tissue and bony overlap, plain films cannot provide detailed anatomic information. Currently, the only indication for plain films of the sinuses is the inability to obtain other imaging modalities such as CT or MRI.
 Figure 28.2 Endoscopic appearance of sinonasal pathology. A: Left septal spur, (B) acute bacterial rhinosinusitis, (C) missed ostium sequence, (D) inverting Papilloma, (E) choncha bullosa. |
Computed Tomography
The emergence of high-resolution CT imaging has advanced our understanding of sinonasal anatomy and physiology, and was fundamental to the rise of ESS (6). The major advantage of CT imaging is the excellent anatomic bony detail it provides. As a result, it has become the gold standard imaging modality for inflammatory diseases of the paranasal sinuses and is essential for preoperative planning.
Imaging the sinuses in the coronal plane is preferred since it provides excellent detail of the OMC; however, significant neck extension during image acquisition makes this position difficult. Therefore, current sinus CT protocols acquire thin axial slice thicknesses, usually less than 3 mm (ideally 1 mm), which permits high-resolution multiplanar reconstruction in the coronal and sagittal planes. Slice thickness of 1 mm is often required for accurate image-guidance compatibility. Intravenous contrast is not used in standard sinus CT protocols; however, it may be utilized during cases when there is a suspected complication of inflammatory disease (such as abscess or thrombosis) or during the evaluation of a sinonasal neoplasm. New multidetector CT scanners allow for acquisition of up to 64 slices with one rotation of the tube. This significantly reduces acquisition times and minimizes motion artifact. Although the radiation dose from a high-resolution CT scan of the sinuses may vary depending on scanning protocol, most yield a dose of 0.96 mSv (7).
A sinus CT can provide helpful diagnostic information in a variety of sinonasal pathologies (Table 28.2). In order to optimize diagnostic yield, it is important to develop a systemic approach to the interpretation of a sinus CT. Although most information is obtained from the coronal plane, helpful information can be obtained from the axial and sagittal images (Table 28.3). Interpretation incorporates a combination of defining the extent of local disease, identifying anatomic variations, and when indicated, surgical planning (8). To optimize bony detail while preserving soft tissue definition, some authors have suggested viewing CT images on a width-level ratio of 2,000/200 (9). The bony contours should be assessed for expansion, erosion, and/or thickening. Bony expansion usually suggests a chronic disease process, while erosion implies a more aggressive, acute pathology. Bony thickening often suggests osteitis resulting from chronic inflammation. Mucosal thickening should be assessed for laterality and extent of sinuses involved. The characteristics of sinus opacification should be noted, as heterogeneity may imply a fungal rhinosinusitis.
TABLE 28.2 COMMON INDICATIONS FOR SINUS CT | ||||||||||
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TABLE 28.3 INFORMATION OBTAINED FROM THE DIFFERENT PLANES OF SINUS CT | ||||||||||||||||||||||||||||||
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Magnetic Resonance Imaging
The technique of MRI involves the application of a strong magnetic field to soft tissue, which results in atom magnetization. Once magnetized, a series of radiofrequency fields are applied, which induce the nuclei to emit a magnetic field specific to each tissue. The scanner detects these differences and produces an image. There are three common MRI sequences, which provide important information: T1-weighted, T2-weighted, and T1-weighted with contrast. Fat appears bright on T1 images, while water is bright on T2 images. Intravenous gadolinium provides an excellent contrast medium, which can provide information regarding the vascularity of tissue.
The major advantages of MRI include: improved soft tissue definition, differentiate between secretions and soft tissue, lack of radiation exposure, and multiplanar reconstruction. The major disadvantages of MRI include: the lack of bony definition, long acquisition time in a small confinement, higher costs, and contraindication with any metal implant (e.g., pacemaker, cochlear implant). Since cortical bone and air both fail to provide a magnetic signal,
MRI cannot differentiate between these two entities. The bony contours of the sinuses and the associated intricate bony lamellae are poorly represented.
MRI cannot differentiate between these two entities. The bony contours of the sinuses and the associated intricate bony lamellae are poorly represented.
TABLE 28.4 COMPARISON OF COMMON SINONASAL RADIOLOGIC MODALITIES | ||||||||||||
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Traditionally, MRI was thought to be overly sensitive when evaluating chronic rhinosinusitis (CRS); however, a recent study by Lin et al. (10) demonstrated that MRI and CT Lund-Mackay scores correlated very well (r = 0.837, p < 0.001). Although MRI may be comparable to CT CRS staging, the lack of bony definition makes surgical planning difficult, and thus precludes its routine use in CRS imaging. The most common indications for MRI include evaluation of: (a) sinonasal mass/neoplasm and (b) suspected intracranial complication of acute rhinosinusitis.
MRI is a useful adjunct during the evaluation of select sinonasal pathologies and is rarely indicated in isolation without obtaining a CT scan. The exquisite soft tissue imaging of MRI combined with the detailed bony anatomy of CT make these two radiographic modalities the ideal options in sinonasal pathology evaluation (Table 28.4).
LABORATORY INVESTIGATIONS
Although most patients with sinonasal pathology do not require routine lab testing, there are certain clinical scenarios whereby the information obtained from lab results can be imperative to the diagnosis and subsequent treatment success. A common scenario where lab testing is indicated is during the evaluation of a young patient with sinus disease and any patient with refractory CRS. Lab testing can identify an underlying congenital abnormality, such as cystic fibrosis (CF) or primary immunodeficiency, or acquired illnesses such as atypical infections and systemic inflammatory diseases.
Cystic Fibrosis Testing
The diagnostic criteria for CF requires the presence of clinical symptoms consistent with CF in at least one organ system, and objective evidence of cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction on any of the following three tests: (a) elevated sweat chloride greater than 60 mmol/L (on two occasions), (b) presence of two disease-causing CFTR mutations on DNA testing, or (c) abnormal nasal potential difference (NPD).
The sweat chloride test remains the primary test used for laboratory confirmation of CF. Sweating is induced by a technique called pilocarpine iontophoresis. It involves placing a pilocarpine-soaked gauze on the skin and applying a gentle electrical current. The current draws pilocarpine into the skin and induces sweat gland secretion. The sweat is then collected and the chloride concentration is quantified (11). For infants older than 6 months, children, and adults, there are three groups of results: (a) Normal (CF very unlikely): ≤39 mmol/L, (b) Intermediate (Possible CF): 40 to 59 mmol/L, and (c) Abnormal (diagnosis of CF): ≥60 mmol/L. The accuracy of sweat chloride testing is operator-dependent and should be performed at experienced labs (12). Patients with an intermediate sweat chloride result should receive DNA analysis, using the multimutation method, to identify a CFTR gene mutation. Approximately 20% of patients with an intermediate sweat test will have an identifiable CFTR mutation on DNA analysis (13). If two CFTR mutations are not identified, then the sweat chloride test should be repeated. A false positive sweat test can occur in any of the following: (a) lab error, (b) malnutrition, (c) dehydration, (d) adrenal insufficiency, (e) hypothyroidism, (f) hypoparathyroidism, (g) mucopolysaccharidosis, and (h) nephrogenic diabetes insipidus. The two most common causes of a false negative sweat test are: (a) lab error and (b) skin edema.
Multimutation genetic testing involves screening at least 23 CF-causing CFTR mutations (14). This panel identifies approximately 90% of CF causing mutations. Molecular analysis should be ordered in cases with an intermediate sweat chloride test. An expanded CFTR mutation panel, deletion evaluation, and/or direct gene sequencing is available for cases when a genetic screen failed to identify
two CF-causing mutations and a repeat sweat test was intermediate (40 to 59 mmol/L).
two CF-causing mutations and a repeat sweat test was intermediate (40 to 59 mmol/L).
The NPD measures CFTR function within the nasal respiratory epithelium. The technique involves the following three measurements of the potential difference across the nasal epithelium: (a) basal state, (b) after nasal perfusion with amiloride (blocks sodium transport—the major component of the NPD), and (c) after nasal perfusion with a chloride-free solution containing isoproterenol (a camp agonist—stimulates CFTR chloride transport). Patients with CF will demonstrate a high basal state potential difference, a large decline with amiloride, and minimal response to isoproterenol. Although not widely available, measuring the NPD is useful in cases where the sweat test and genetic analysis results are inconclusive but atypical CF is suspected due to clinical presentation in one or more organs.
Other rare tests for CF include pancreatic function analysis, such a 72-hour stool collection for fecal fat analysis. Pulmonary function tests and bronchoalveolar lavages can be helpful to define the extent of pulmonary disease.
Primary Immunodeficiency Testing
Immunologic testing can evaluate both the cellular and humoral immune systems. Immune dysfunction is common in patients with refractory CRS (15), therefore, knowledge of the available immune testing options is important.
Humoral immunity testing involves both quantifying immunoglobulin (Ig) levels and assessing for a functional immunoglobulin deficiency. Measurements of serum IgG, IgA, and IgM along with IgG subclasses are helpful to quantify a humoral deficiency. The significance of an IgG subclass deficiency remains controversial, while current recommendations state that it is not significant unless it is associated with an impaired specific antibody response. A functional immunoglobulin deficiency is evaluated by assessing the antibody response following administration of an unconjugated polysaccharide vaccine, such as pneumovax. For adults, a functional immunoglobulin deficiency is diagnosed if there was a lower than fourfold increase in antibody titers to 70% of the serotypes tested (16).
Cellular immunity is mediated by T cells and deficiencies with this system often result in severe infections. The complete blood count (CBC) is useful to identify a lymphopenia and other hematologic defects. Flow cytometry uses cell surface markers to evaluate lymphocyte subpopulations and provide subset quantitative information. The cutaneous delayed-type hypersensitivity test is an in vivo test measuring the recall response to an intradermal injection of an antigen, which the patient has previously been exposed.
