Description
Mucosa-associated lymphoid tissue lymphoma (MALToma) is a type of non-Hodgkin’s B-cell lymphoma that arises from the marginal zone of lymphoid tissue. It is usually low-grade and extranodal, often affecting the stomach. MALToma is often associated with chronic inflammation, particularly Helicobacter pylori infection in gastric cases.
Pathogenesis
MALTomas are usually associated with chronic inflammation or autoimmune diseases. In gastric MALTomas, chronic infection with H. pylori leads to the formation of MALT and subsequent transformation into lymphoma. Translocations, such as the t(11;18) involving the API2 and MALT1 genes, have been identified in a subset of cases.
Subtypes
MALTomas can occur at various sites, the most common being the stomach. Other sites include the lung, thyroid, salivary gland, ocular adnexa, and skin.
Epidemiology, Risk Factors & Associations
- MALToma accounts for about 5-8% of all B-cell lymphomas.
- Associated with H. pylori infection in gastric MALTomas (85-90%).
- Autoimmune diseases like Sjogren’s syndrome and Hashimoto’s thyroiditis are also risk factors.
Clinical Features
- Symptoms are variable, depending on the site of the tumour.
- Gastric MALTomas may present with nonspecific abdominal discomfort or dyspepsia.
Complications
- Local invasion and distant metastasis are possible in advanced disease.
Pathological Features
Histopathology
- Macroscopic: MALTomas are often superficial and show a diffuse or nodular growth pattern.
- Microscopic: Characterised by the proliferation of small B-lymphocytes, plasma cells, and scattered larger B-cells (centrocyte-like cells).
Radiological Features
General Features
- Typically demonstrates a mass or thickening at the site of the tumour.
- May show a diffuse or nodular pattern of involvement.
- Often associated with features of the underlying chronic inflammatory condition.
CT
- Non-contrast: May show mass or thickening at the site of the MALToma.
- Contrast-enhanced: Usually shows moderate enhancement.
MRI
- T1: Tumour is usually iso- to hypointense compared to muscle.
- T2: Typically hyperintense.
- T1 C+: Shows enhancement.
PET FDG
- MALTomas usually show FDG uptake.
Grading and Staging
Staging is typically based on the Ann Arbor staging system used for non-Hodgkin lymphomas.
Diagnosis
Diagnosis involves a combination of endoscopic or image-guided biopsy, histopathology, immunophenotyping, and often molecular genetic studies.
Differential Diagnosis
- Other lymphomas: Diffuse large B-cell lymphoma may also present as a mass with similar imaging features but is typically more aggressive.
- Gastritis or peptic ulcer disease: These can mimic the findings of gastric MALToma.
Management
- Localised disease is often treated with eradication therapy for H. pylori in gastric cases.
- Radiation therapy, chemotherapy, and immunotherapy can be used for more advanced or refractory disease.