Diagnosis and Staging
Criteria for lymphomatous involvement by CT
Defining strict CT size criteria for the establishment of lymphomatous nodal involvement is complicated by a number of factors, such as overlap between benign reactive hyperplasia and malignant lymphadenopathy and obliquity of node orientation to the scan plane. Additional difficulties more specific to children include greater variability of normal nodal size with body region and age and the frequent occurrence of reactive hyperplasia.
General concepts to consider in regard to defining lymphomatous involvement by CT include the following:
- Contiguous nodal clustering or matting is highly suggestive of lymphomatous involvement.
- Any focal mass lesion large enough to characterize in a visceral organ is considered lymphomatous involvement unless the imaging characteristics indicate an alternative etiology.
- North American protocols have used a consistent size criteria: A measurable lesion by CT is defined as one that can be accurately measured in two orthogonal dimensions, which typically requires a lesion at least 1 cm in diameter for extranodal sites; lymph nodes are considered abnormal if the long axis is 1.5 cm or greater or between 1.1 cm and 1.5 cm with a short axis of at least 1.0 cm.
- Criteria for nodal involvement may vary by cooperative group or protocol. For example, in the Society for Paediatric Oncology and Haematology (Gesellschaft für Pädiatrische Onkologie und Hämatologie [GPOH]) completed study (GPOH-HD-2002), nodal involvement was defined if the node was greater than 2 cm in largest diameter. The node was not involved if it was less than 1 cm and was considered questionably involved if it was between 1 cm and 2 cm. Involvement decision was then based on all further clinical evidence available.
The recommended functional imaging procedure for initial staging is now PET.[4,5] In PET scanning, uptake of the radioactive glucose analog, 18-fluoro-2-deoxyglucose (FDG) correlates with proliferative activity in tumors undergoing anaerobic glycolysis. PET-CT, which integrates functional and anatomic tumor characteristics, is often used for staging and monitoring of pediatric patients with Hodgkin lymphoma. Residual or persistent FDG avidity has been correlated with prognosis and the need for additional therapy in posttreatment evaluation.[6,7,8,9]