CERVICAL ADENOPATHY: REACTIVE AND INFECTIOUS
- Reactive adenopathy is a common finding on imaging studies and in young children can be considered “physiologic.”
- Reactive adenopathy may be distinguished from lymphoproliferative, metastatic, and infectious adenopathy with imaging in many cases based on the distribution and morphology of the pathologic nodes.
- Causative pathology for the adenopathy may be seen on the study.
- Reactive adenopathy may evolve to more specific expressions of the disease process, such as suppurative adenopathy in pyogenic infections.
- Reactive adenopathy and that due to lymphoproliferative disease may not be distinguishable on any imaging study, and follow-up, at least by clinical examination, is essential to exclude a malignant etiology.
- The imaging study may provide clues as to the etiology of infectious adenopathy.
- The imaging study may show extranodal complications of infectious adenopathy.
Reactive nodes range from incidental findings to a feature that is useful in the differential diagnosis to a situation that must be distinguished from significant treatable pathology. At times, such adenopathy must initially be distinguished from malignant adenopathy (Chapter 157) and that due to benign systemic diseases (Chapter 159) as well as other lateral compartment masses such as infected branchial apparatus cysts (Chapter 153).
The primary presentation of reactive adenopathy is most often a perceived “solitary” neck mass of uncertain etiology or generalized palpable lymph node prominence without associated signs or symptoms or other physical findings. More often, physical examination will reveal multiple abnormal nodes—either unilateral or bilateral—depending on the etiology.
Tenderness and fever may be present and are much more likely in infectious and noninfectious inflammatory conditions (Chapters 13, 16, 17–20, and 159). For infectious adenopathy, an inciting condition such as pharyngitis or skin infection may be a prominent part of the presentation.
The anatomy of interest is discussed in detail in Chapter 149 and reviewed with a focus on metastatic adenopathy in Chapter 157 and with regard to its application in evaluating neck masses of uncertain etiology or due to an “unknown primary.”
The techniques for computed tomography (CT) and magnetic resonance (MR) studies of the infrahyoid neck for various clinical situations, including lymphadenopathies, are presented in Appendixes A and B. Standard ultrasound imaging and flow-related techniques are used with transducers appropriate for the depth of penetration required. The rationale for these protocols is presented specifically in Chapter 149.
The approach with radionuclide studies depends on the specific aim of the examination. Most current usage is limited to known or suspected cancer evaluation with fluorine-18 2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET). The use of FDG-PET should be very limited, if used at all, in conditions that are likely to be inflammatory since the diagnosis will be established by a combination of the clinical setting, imaging, and tissue sampling of the nodes or aspiration when necessary. Reactive and infectious nodes are likely to be hypermetabolic regardless of the etiology because the process will activate immune-competent cells in the nodes, by definition making the cells hypermetabolic and therefore fluorine-18 2-fluoro-2-deoxy-D-glucose (FDG) avid. Reactive nodes are a common source of false-positive findings in patients with head and neck cancer.
PATHOPHYSIOLOGY AND PATTERNS OF DISEASE
Reactive nodes generally will enlarge and retain an otherwise normal architecture (Fig. 158.1). The vascular pedicle typically will enlarge, and flow will be increased via the hilar vascular pedicle. The capsule of the lymph node may also manifest the physiologic hypervascularity of the node. Measurable CT, MR, and ultrasound parameters will manifest variable degrees of hypervascularity as increased blood flow by whatever parameter chosen1–7 (Fig. 158.2).
Infectious nodes may undergo focal and diffuse architectural changes. In pyogenic infections, this will reflect a cellulitic type or “presuppurative” phase followed by various degrees of liquefaction that tends to be central but may be more peripheral within the node (Fig. 158.2). Depending on the virulence of the infection, host factors, and treatment status, there will be capsular reactive changes and perinodal inflammatory changes (Figs. 158.2–158.7). At some point, the suppurative node becomes equivalent to an abscess, or purulent material can rupture from the node and produce a true deep neck abscess (Fig. 158.3G,H). Later-stage or healing changes may include dystrophic calcification (Fig. 158.6). Viral infections will result in typically reactive-appearing nodes with little, if any, capsular or perinodal findings suggestive of infection (Fig. 158.1). Lower-grade or partially treated infectious adenopathy may show a hybrid reactive-suppurative appearance (Figs. 158.7–158.9).