MRI of primary non-Hodgkin's lymphoma of the palatine tonsil.

Non-Hodgkin's lymphoma (NHL) arising primarily in the palatine tonsil is uncommon. The aims of the study were to describe the appearances on MRI and to identify the features that help to distinguish NHL from other tonsillar tumours. The clinical records and MR images of eight patients with primary NHL of the palatine tonsil were reviewed. Patients had a short duration of symptoms (mean 1 month). Systemic symptoms (fever, weight loss or night sweats) occurred in two patients. Tumours were round or lobulated and ranged in size from 30 mm to 70 mm. The signal intensity on T2 weighted, T1 weighted and T1 weighted contrast enhanced images was homogeneous and similar to that of normal tonsil in six patients. Two large tumours were mildly heterogeneous and one of these showed small foci of necrosis. NHL of the tonsil displaced rather than invaded local structures in seven patients and locally invaded the soft palate in only one patient. Lymphadenopathy was present in five patients and the nodes were of similar signal intensity to the primary tumour. There was involvement of the ipsilateral upper internal jugular chain in all cases of lymphadenopathy. The posterior triangle was involved in two patients, the periparotid node in one patient and the retro-oropharyngeal region in one patient. The presence of a large tumour without deep invasion together with homogeneous non-necrotic nodes suggests the diagnosis of NHL. As NHL frequently has similar signal intensity to normal tonsil, MRI may not be able to detect lymphomatous involvement in the non-enlarged tonsil.