Intestinal inflammatory pseudotumour with regional lymph node involvement: identification of a new bacterium as the aetiological agent

Abstract

Inflammatory pseudotumours are the morphological expression of diverse processes such as reactive/reparative, infective, and neoplastic. This paper reports an example of intestinal inflammatory pseudotumour, with identification of a newly characterized bacterium in the lesion. The patient presented with intestinal obstruction. Laparotomy revealed a tumour in the terminal ileum causing stricture, and multiple enlarged regional lymph nodes. Histologically, the tumour and lymph nodes were composed of plump spindle cells disposed in a vague storiform pattern, and associated with lymphocytes and plasma cells. Immunohistochemical studies showed that most of the spindle cells were histiocytes (CD68 positive), prompting a search for a bacterial aetiology, akin to mycobacterial spindle cell pseudotumour. All histochemical stains for micro-organisms were unrewarding. Ultrastructural studies, however, revealed abundant bacteria within the spindle histiocytes. Polymerase chain reaction, using conserved oligonucleotide primers complementary to the 16S rRNA genes of eubacteria, was employed to amplify 16S rRNA gene fragments directly from the involved lymph node tissue. Phylogenetic analysis of the amplified DNA sequences revealed an organism with 99% sequence conformity to Pseudomonas veronii, a bacterium which has hitherto not been implicated in human infection. The importance of searching for an infective agent in inflammatory pseudotumour in the appropriate setting is re-emphasized.