Inflammatory myofibroblastic tumour - A rare cause of right iliac fossa mass

Clinical History

40-year-old male patient with complaints of pain in the right iliac fossa for 2 weeks. No history of vomiting or altered bowel habits. History of low grade fever.
On examination, diffuse tenderness in the right iliac fossa with a mass was felt. Clinical diagnosis of appendicular mass was made.

Imaging Findings

Abdominal Ultrasonography revealed a well defined heterogenous mass lesion in the right iliac fossa with no significant vascularity on Doppler evaluation. Probe tenderness was present.

Further contrast enhanced CT of the abdomen was done which showed a mass lesion involving the omentum in the right iliac fossa measuring 6 x 4 x 6 cm just beneath the anterior abdominal wall with surrounding inflammatory changes in the form of fat stranding. Plain images showed hyperdense areas suggestive of haemorrhage. Minimal post contrast enhancement was seen. The caecum, terminal ileum and appendix were all separately visualised and appeared normal.

The patient underwent surgery and the mass lesion in right iliac fossa was resected and sent for histopathological examination. A pathological differential diagnosis of inflammatory myofibroblastic tumour/ gastrointestinal stromal tumour (GIST) was suggested. Further immunohistochemistry study was performed which was negative for CD 117 confirming the lesion as an IMT.

Discussion

Inflammatory myofibroblastic tumour (IMT) is a rare chronic inflammatory lesion of unclear pathogenesis. This condition was first observed by Brunn in 1939 and was named so by Umiker in 1954. It is also known as inflammatory pseudotumour, plasma cell granuloma, pseudotumour and inflammatory fibrosarcoma [1, 2]. It affects individuals of all ages with no sex predilection. Inflammatory myofibroblastic tumour is most commonly seen in the lung and the orbit. Other rare sites of IMT include the mesentery, omentum, retroperitoneum, gastrointestinal and genitourinary tracts. [3, 4]

The aetiology of inflammatory myofibroblastic tumour is unclear - whether it is a post inflammatory process or true neoplasm remains controversial. However, most common aetiologic factors are sequelae of occult infection, minor trauma or prior surgery. [5, 1, 3]

Imaging characteristics are usually nonspecific. It is usually a slow growing circumscribed mass lesion. On ultrasonography, they appear as well defined mass lesions with heterogenous echotexture and no significant vascularity on Doppler evaluation. [1, 3]

On CT, they usually appear as well defined mass lesions with heterogeneous attenuation. On post contrast images, they display a spectrum of enhancement patterns, ranging from non enhancing to heterogeneously enhancing and peripherally enhancing lesions. Few of them may show central necrotic areas and calcifications. [1, 3]

Diagnosis is usually made by exclusion and characteristic microscopic features like abundant inflammatory cells and myofibroblastic spindle cells. [1, 2, 5]

Differential diagnoses in the abdomen include benign fibrous mesenteric tumours such as desmoids, GIST, lymphoma, metastatic disease and soft tissue sarcoma in adults. Histopathological findings of IMT and GIST are similar- immunohistochemistry helps in the differentiation as GIST are CD 117 positive. In children, the most common differential for this condition is embryonal rhabdomyosarcoma. [1]

Even though there are no characteristic imaging findings, one has to keep in mind the possibility of inflammatory myofibroblastic tumour as a differential diagnosis for omental lesions and lesions in the right iliac fossa. CT is helpful to exclude pathologies of the caecum, terminal ileum and appendix and localise the lesion to the omentum.

Surgical resection is the treatment of choice for most cases. [6]

Differential Diagnosis List

Final Diagnosis

Inflammatory myofibroblastic tumour of the omentum (right iliac fossa)

URL:	https://eurorad.org/case/9919
DOI:	10.1594/EURORAD/CASE.9919
ISSN:	1563-4086