Diagnosis and Staging
General concepts to consider in regard to defining lymphomatous involvement by FDG-PET include the following:
- Concordance between PET and CT data is generally high for nodal regions, but may be significantly lower for extranodal sites. In one study specifically analyzing pediatric Hodgkin lymphoma patients, assessment of initial staging comparing PET and CT data demonstrated concordance of approximately 86% overall. Concordance rates were significantly lower for the spleen, lung nodules, bone/bone marrow, and pleural and pericardial effusions.
- Integration of data acquired from PET scans can lead to significant changes in staging. In the previously mentioned study, PET findings resulted in a change in staging in 50% of patients (with a nearly equal number of patients up- and down-staged), and subsequent adjustments in involved-field radiation therapy treatment volumes in 70% of patients (more likely an addition rather than exclusion).
- Staging criteria using PET and CT scan information is protocol dependent, but generally areas of PET positivity that do not correspond to an anatomic lesion by clinical examination or CT scan size criteria should be disregarded in staging.
- A suspected anatomic lesion which is PET-negative should not be considered involved unless proven by biopsy.
FDG-PET has limitations in the pediatric setting. Tracer avidity may be seen in a variety of nonmalignant conditions including thymic rebound commonly observed after completion of lymphoma therapy. FDG-avidity in normal tissues, for example, brown fat of cervical musculature, may confound interpretation of the presence of nodal involvement by lymphoma.
Establishing the Diagnosis of Hodgkin Lymphoma
After a careful physiologic and radiographic evaluation of the patient, the least invasive procedure should be used to establish the diagnosis of lymphoma.
Key issues to consider in choosing the diagnostic approach include the following:
- If possible, the diagnosis should be established by biopsy of one or more peripheral lymph nodes. Aspiration cytology alone is not recommended because of the lack of stromal tissue, the small number of cells present in the specimen, and the difficulty of classifying Hodgkin lymphoma into one of the subtypes.
- An image-guided biopsy may be used to obtain diagnostic tissue from intra-thoracic or intra-abdominal lymph nodes. Based on the involved sites of disease, alternative noninvasive procedures that may be considered include thoracoscopy, mediastinoscopy, and laparoscopy. Thoracotomy or laparotomy is rarely needed to access diagnostic tissue.
- Patients with large mediastinal masses are at risk of cardiac or respiratory arrest during general anesthesia or heavy sedation. After careful planning with anesthesia, peripheral lymph node biopsy or image-guided core-needle biopsy of mediastinal lymph nodes may be feasible using light sedation and local anesthesia before proceeding to more invasive procedures. Care should be taken to keep patients out of a supine position. Most procedures, including CT scans, can be done with the patient on his or her side or prone.
- If airway compromise precludes the performance of a diagnostic operative procedure, preoperative treatment with steroids or localized radiation therapy should be considered. Since preoperative treatment may affect the ability to obtain an accurate tissue diagnosis, a diagnostic biopsy should be obtained as soon as the risks associated with general anesthesia or heavy sedation are alleviated.
- Because bone marrow involvement is relatively rare in pediatric Hodgkin lymphoma patients, bilateral bone marrow biopsy should be performed only in patients with advanced disease (stage III or stage IV) and/or B symptoms.
Ann Arbor Staging Classification for Hodgkin Lymphoma
Stage is determined by anatomic evidence of disease using CT scanning in conjunction with functional imaging. The staging classification used for Hodgkin lymphoma was adopted at the Ann Arbor Conference held in 1971  and revised in 1989. Staging is independent of the imaging modality used.