Trachea: Benign and Malignant Tumors
- Computed tomography and magnetic resonance imaging are critical to the treatment planning for tracheal tumors.
- Magnetic resonance is superior to computed tomography for demonstrating the relationship of tumor to the tracheal wall, hypopharynx, esophagus, and thyroid gland.
- Computed tomography and magnetic resonance imaging can provide information about the initial airway status and possible cumulative risk of further airway compromise associated with manipulation and treatment of the tumor.
Intrinsic tracheal tumors (Figs. 212.1–212.3) are uncommon, and benign tumors are rare except for papillomas (Figs. 212.4 and 212.5). The trachea is far more commonly secondarily involved by spread of tumors from adjacent sites of origin— most commonly the larynx, hypopharynx, and thyroid gland—than a primary site (Figs. 212.6–212.12). Squamous cell carcinoma (SCCA) is the most common primary tracheal malignancy (Fig. 212.3) followed by adenoid cystic (carcinoid) (Fig. 212.2) and mucoepidermoid carcinoma (Fig. 212.1). Tracheal metastases occur rarely but virtually always occur in the setting of a known primary (Fig. 212.13). Approximately 10% of primary tracheal tumors are benign (Figs. 212.4 and 212.5). The most common benign tumor is by far the squamous papilloma associated with viral exposure (Fig. 212.4). Other benign tumors included pleomorphic adenoma, granular cell tumor, and those of cartilage origin.
Staging and medical decision-making procedures for tracheal tumors include endoscopy with biopsy, contrast-enhanced computed tomography (CECT) or contrast-enhanced magnetic resonance (CEMR) depending on the practice preference, and a chest x-ray. Imaging studies are an essential component of the clinical and diagnostic evaluation, providing unique and often pivotal information that complements the clinical examination. Imaging provides additional information concerning the deep extent and regional spread of disease. Chest computed tomography (CT) and fluorine-18 2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) may provide additional information in selected cases.
This chapter describes the important role of diagnostic imaging in clinical decision making for primary tracheal tumors. Those arising from adjacent organs are summarized and illustrated for completeness but are discussed in dedicated chapters about tumors arising from those other primary sites.
A thorough knowledge of tracheal anatomy and anatomic variations in each of the following areas is required for the evaluation of tracheal tumors. This anatomy is presented in detail with the introductory chapters on the trachea, larynx, hypopharynx, cervical esophagus, and infrahyoid neck in general:
Evaluation of the Trachea and Closely Related Organs Frequently Involved with Contiguous Disease in these Tumors
- Trachea (Chapter 209)
- Larynx, including the laryngeal skeleton and deep tissues spaces, especially those of the subglottis (Chapter 201)
- Hypopharynx (Chapter 215)
- Cervical esophagus and its membranous wall in common with the trachea and both of their relationships to the postcricoid portion of the hypopharynx (Chapter 221)
Evaluation of Spread Beyond the Trachea
- Visceral compartment of the neck and related fasciae (Chapter 149)
Evaluation of Regional Lymph Node Disease
- Detailed knowledge of normal node and perinodal morphology and the common drainage pathways of tracheal cancer, which emphasizes node levels 4 through 6 and the mediastinal groups (Chapters 149 and 157)
Evaluation of Perivascular and Perineural Spread
- Knowledge of the entire course of the vagus and inferior laryngeal neurovascular bundle, including the recurrent laryngeal nerves on both sides (Chapter 201)
Techniques and Relevant Aspects
The trachea is studied in essentially the same manner for tumors as it is for the evaluation of known or suspected laryngeal or thyroid cancer. Study of the trachea for tumors should be continued to the carina so that the entire trachea and contiguous mediastinal node groups are included.
The principles of using these studies are reviewed in Chapters 69, 172, 201, and 206. Specific problem-driven protocols for CT and magnetic resonance imaging (MRI) of the trachea, larynx, hypopharynx, and thyroid gland tumors are presented in Appendixes A and B, respectively.
There is little or no use for ultrasound in studying these tumors.
FDG-PET may be useful in selected cases once a diagnosis of malignancy is established by biopsy. In some cases, it might be used before biopsy or on the basis of anatomic imaging findings to establish a risk profile for malignancy.
Pros and Cons
Evaluation of Submucosal or Other Masses of Uncertain Etiology
Benign masses limited to the trachea and malignant tumors have essentially the same initial presentation. Any presentation, regardless of potential etiology, that is suspicious for a tracheal mass should eventually be studied with CT or MRI as the clinical evaluation directs the workup (Figs. 212.1–212.5 and 212.13). MRI can be used initially, if preferred, but is more likely to be degraded than CT studies and is sometimes rendered nondiagnostic due to motion artifacts. A preferred approach might be to use a supplemental magnetic resonance (MR) study in a localized area of interest, where it might add meaningful incremental data as directed by findings on an initial CT. In this way, the strengths of MRI related to better soft tissue contrast resolution may be exploited to optimally answer questions that aid precise surgical or alternative planning (Fig. 212.1).
Integrity of the Airway
Any imaging study of a diseased trachea must be evaluated for the disease effect on the airway. The anatomic status of the airway, as well as the risk of any acute adverse complication, such as the potential for rapidly progressive airway obstruction either by the mass or a potential airway complication that might arise as a result of biopsy, should be reported (Figs. 212.7 and 212.10). For instance, biopsy of an unanticipated hypervascular mass could lead to an unfortunate amount of hemorrhage and aspiration of blood. More likely, a mass that nearly occludes the airway completely could swell with biopsy and complete the occlusion; imaging might help to anticipate the necessity for at least temporary airway control following the biopsy, so the patient will have an understanding of the odds of that happening (Figs. 212.7 and 212.10). Multiplanar and virtual endoscopic processing of images can help to obviate some endoscopic and bronchoscopy procedures (Fig. 212.4) for at least gross airway assessment, even though such virtual anatomic studies lack dynamic information and only provide indirect functional information, with the latter based on the degree of reduction of airway cross-sectional area.