Imaging of incidentally discovered ossifying fibromyxoid tumour of retroperitonuem with histopathological correlation: a rare case report

Clinical History

A 35-year-old male patient came to the Surgery Out Patient Department with pain in the left iliac region and increasing during micturition and one episode of haematuria. No fever, malaise, weight loss. Vital signs were stable. No evidence of any palpable mass per abdomen. No tenderness, guarding, rigidity. External genitalia were normal.

Imaging Findings

On ultrasound there was left sided hydro-ureteronephrosis, with a 10-12 mm calculus in the left vesico-ureteric junction. Complete course of the ureter was suboptimally visualized. Therefore the patient was scheduled for CT.
CT findings other than the left VUJ calculus and hydroureteronephrosis showed a well-defined rounded mass lesion in the left hypogastrium retroperitoneally in the para-aortic region. Contrast study showed inhomogeneous enhancement with central non-enhancing focus within. Delayed study showed persistent enhancing areas. Few specks of calcification were also seen within. A diagnosis of mesenchymal retroperitoneal tumour was made.
Patient underwent ureteroscopic lithotripsy to relieve the hydronephrosis. Later the retroperitoneal lesion was resected under laparoscopic guidance.
Grossly the tumour was well encapsulated and had distinct margins with the adjacent structures. However, there was a small pedicle-shaped attachment to the psoas muscle inferiorly, with vascular channels which were ligated before resection. The specimen was sent for histopathological and immunohistochemistry which established the final diagnosis.

Discussion

Ossifying fibromyxoid tumour (OFMT) is a rare soft tissue tumour with an atypical presentation in the retro-peritoneum with only a single case report published by Teilchl Motoyama et al. [1]
The majority of cases of OFMT show non aggressive behaviour both in clinical and histo-pathological analysis. [2]

Enzinger et al found in their study that 70% of cases in OFMT will show positive Vimentin and S-100 protein positive. [2]. Both of these protein markers were positive in our specimen.

The cells of this lesion may express leu7, neuron specific enolase and glial fibrillary acidic proteins well. [3]

Imaging findings of this mass lesion are not properly defined in standard literature due to the rarity of OFMT. Plain Radiograph KUB may show an ill-defined soft tissue opacity with radiodense foci within.
Erosion or periosteal reaction of the underlying bone is infrequently seen. CT scans will clearly show peripheral or intralesional ossification. [4]
Specific gene translocation is classical for OFMT. A recent fluorescence in situ hybridization (FISH) study revealed INI-1 tumour suppressor gene deletion in 71% of cases. [5]
PHF1 (at 6p21) is routinely rearranged in OFMT, including all the atypical and aggressive variants. [6]
These tests are not advised routinely and only used to confirm the biopsy diagnosis with certainty and rule out more devastating pathologies encountered in the region.
Surgical excision followed by clinical and imaging follow-up is considered to be correct management until further guidelines are established. [7] No recurrence of the lesion is seen in our case after 18 months of post-surgical monitoring.

LEARNING POINTS:
OFMT is a rare soft tissue tumour and can be possibly seen in the retro-peritoneum. And in imaging, if a lesion with central or peripheral calcification and typical delayed persistent contrast enhancement is seen, ossifying fibromyxoid tumour should also be considered when all the more common tumours are excluded.
Mostly they are benign and compliant to surgery and have a good outcome.
Biopsy with IHC is confirmative when this is suspected.

Differential Diagnosis List

Final Diagnosis

Ossifying fibromyxoid tumour of the retroperitoneum

URL:	https://www.eurorad.org/case/13859
DOI:	10.1594/EURORAD/CASE.13859
ISSN:	1563-4086