Saturday, July 16, 2011

FDG-PET and Peripheral T-Cell Lymphomas

T-cell neoplasms are broadly divided by the World Health Organization into precursor T-cell neoplasms and peripheral T-cell neoplasms. Peripheral T-cell neoplasms are further divided into peripheral T-cell leukemias and peripheral T-cell lymphomas. The latter is the subject of this post.

Peripheral T-cell lymphomas are uncommon neoplasma that make up about 10%-25% of all cases of non-Hodgkin lymphoma, although the prevalence has geographic variability. T-cell lymphomas tend to have a poorer prognosis than B-cell lymphomas, but vary in their behavior, from indolent to aggressive.

Peripheral T-cell lymphomas can be subdivided into primary nodal disease and primary systemic (extranodal) disease. The main clinicopathologic presentations of peripheral T-cell lymphomas include:

  • Extranodal NK/T-cell lymphoma, nasal type: Previously known as angiocentric lymphoma and lethal midline granuloma, this is the most common peripheral T-cell lymphoma in Asian patients, and has been associated with the Epstein-Barr virus. The nasal cavity or paranasal sinuses are often involved, with tumor necrosis a common feature, but identical tumors can also be found in the skin, lymph nodes, and viscera, sometimes in isolation.
  • Enteropathy-type T-cell lymphoma: This rare subtype typically occurs in elderly patients with a history of celiac disease or dermatitis herpetiformis. PET scan may reveal FDG-avid lesions in the gastrointestinal tract and mesenteric lymph nodes.
  • Subcutaneous panniculitis-like T-cell lymphoma: Multifocal subcutaneous infiltrates of malignant T lymphocytes are associated with benign histiocytic inflammatory cells. CT may show poorly defined subcutaneous lesions ranging in size from a few centimeters to large confluent infiltration. The omental fat can also be involved. The lesions are FDG-avid. Inflammatory disorders of the subcutaneous tissues, such as erythema nodosum and erythema induratum, and inflammatory or infectious panniculitis can have a similar appearance.
  • Mycosis fungoides (shown above)/Sézary syndrome: This is a cutaneous T-cell lymphoma that exists in three clinical phases: patches, plaques, and tumors. PET can demonstrate plaques and tumors, but particular attention has to be devoted to the skin. On CT, the appearance varies from cutaneous thickening to exophytic soft-tissue masses (see above image). FDG-avid adenopathy can be seen in some patients.

    Sézary syndrome is the leukemic variant of mycosis fungoides, with characteristic Sézary cells found in the peripheral blood. Patients present with diffuse erythroderma; however, PET may not always show diffusely increased cutaneous FDG uptake. When present, diffusely increased cutaneous FDG uptake is similar to the appearance of nonattenuation-correction PET emission images. Patients typically have FDG-avid lymphadenopathy; however, low-grade FDG uptake in lymph nodes may represent benign dermatopathic lymphadenitis (reactive enlargement of lymph nodes draining areas of disrupted skin) and be mistaken for positive nodal disease.
  • Anaplastic large cell lymphoma, primary cutaneous type: Part of the spectrum of disease that includes lymphomatoid papulosis (benign). Patients typically present with persistent cutaneous nodules 1 cm – 2 cm in size, and, in ~10% of cases, extracutaneous disease.
  • Hepatosplenic T-cell lymphoma: This is a rare, recently described subtype with an aggressive course and poor prognosis. Patients have hepatosplenomegaly without lymphadenopathy and significant cytopenia.
  • Anaplastic large cell lymphoma, primary systemic type: The majority have FDG activity in the lymph nodes. Patients may also have foci of cutaneous or subcutaneous FDG uptake, as well as visceral disease. Expression of anaplastic lymphoma kinase (ALK) protein suggests a better prognosis than the other peripheral T-cell lymphomas. However, no obvious association has been found between expression of this protein and FDG avidity of tumors.
  • Angioimmunoblastic T-cell lymphoma: This is a distinct subtype that presents with lymphadenopathy, hepatosplenomegaly, skin rash, and constitutional symptoms, with evidence of dysregulation of the immune system (hypergammaglobulinemia, Coombs-positive hemolytic anemia, and immunodeficiency). As suggested by the name, patients have FDG-avid adenopathy. Some patients may have visceral involvement, including the spleen. FDG-avid skin lesions are typically not seen.
  • Peripheral T-cell lymphoma, not otherwise specified: No specific clinicopathologic features to permit further classification. The majority have FDG-avid lesions and FDG-avid lymphadenopathy. Patients may also have cutaneous and visceral disease.


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