Pulmonary Pathology Online
Pathology of Pulmonary B-Cell Non-Hodgkin's Lymphoma of MALT Origin
Although the lung is frequently involved by disseminated lymphoma, isolated pulmonary lymphoma is rare, accounting for less than 1% of all extranodal localized disease.
Three broad categories of lymphoma of the lung require recognition:
-In rare instances, large B cell type lymphoma can present primarily in the lung ;
-A second variant is by T cell lymphoma presenting as an angiocentric process.
- However, the most common histologic subtype is represented by low-grade mucosa-associated lymphoid tissue (MALT) lymphoma, often in the past considered as a pseudotumor because of its long indolent natural history.
In 1963, Salzstein distinguished pulmonary lymphoma from "pseudolymphoma". Pseudolymphoma was regarded as a reactive condition similar to pseudolymphomas seen at other sites.
Most cases are now thought to be neoplastic from onset and arise from pulmonary MALT.
Age and sex:
Patients present in their fifth to seventh decades. It is slightly more common in male.
In low-grade disease, the commonest presentation is an asymptomic mass on routine chest x-ray.
High-grade lymphomas are however, nearly always symptomatic.
Constitutional symptoms include weight loss, fever and night sweats.
Previous or synchronous MALT lymphoma at other extranodal sites may be present.
Unlike gastric lymphomas where there is a clinical association with previous Helicobacter pylori infection, there is no consistent clinical association with pulmonary counterparts.
Some cases of pulmonary lymphomas have been described in patients with autoimmune disorders, some with fibrosing alveolitis.
Surgical lung biopsies and resection have been the commonest diagnostic procedures.
Identification of gene rearrangements using the polymerase chain reaction has successfully proven monoclonality in bronchoalveolar lavage fluid and both bronchoscopic and transbronchial biopsies, in situations where previous diagnoses had been classified as equivocal.
Low-grade tumours are composed of centrocyte-like, lymphocyte-like or monocytoid cells.
These are all thought to be variations of the same neoplastic cell.
Features of plasmacytoid differentiation are often seen in the smalll lymphocytes, and Russell or Dutcher bodies may be present.
A distinguishing feature of the lymphoid cell population is the presence of a rim of clear cytoplasm surrounding the nucleus of the cells, resembling that of centrocytes or monocytoid B-cells.
In resection specimens, and to a lesser extent in open lung biopsies, a characteristic pattern of spread along bronchovascular bundles and interlobular septa is seen.
Subsequent expansion and destruction of the alveolar walls and filling of the alveolar spaces give rise to nodules that coalesce centrally, often with hyaline sclerosis towards their centers.
Reactive follicles with well-formed germinal centers may be seen in 70% of cases
Other features of MALT lymphomas, such as lymphoepothelial lesions, are often seen.
This pattern of spread is not seen in high-grade tumours, in which the infiltrate is more diffuse and destructive.
Giant lamellar bodies may be rarely noted.
Necrosis is almost always limited to the high-grade tumors.
The neoplastic cells are of B-cell phenotype with a variable reactive T-cell population in the background.
Light chain restriction is observed in 30-70% of cases.
Amplification of the immunoglobulin heavy chain gene with the polymerase chain reaction has shows monoclonality in 60% of low-grade lymphomas, but only occasionally in high-grade disease.
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