Haemangiopericytoma/solitary fibrous tumour of the greater omentum.
A 41-year-old woman was admitted to George Mukhari Academic Hospital, Limpopo Province, South Africa, with complaints of a distended abdomen, early satiety and episodic postprandial vomiting. She had noted gradual enlargement of her abdomen over the past 3 years, attributing it to her 'recent pregnancy. The pregnancy had turned out to be a molar pregnancy, and an intra-abdominal mass had also been present. The molar pregnancy was successfully treated with uterine evacuation, but the patient had not attended for further investigation of the intra-abdominal mass.
On general examination the patient appeared healthy. Abdominal examination revealed a non-tender, nodular, very mobile (from side to side and up and down) mass filling the entire abdominal cavity. She had normocytic, normochromic anaemia, with a haemoglobin concentration of 7.6 g/dL. Other laboratory results were normal, including beta-human chorionic gonadotrophin, carcinoembryonic antigen, carbohydrate antigen 19.9 and alpha-fetoprotein. An abdominal contrast-enhanced computed tomography (CT) scan showed a large abdominopelvic vascular heterogeneous mass with multiple cystic and necrotic areas (Figs 1 and 2). The origin of the mass could not be established on the CT scan. At laparotomy via a midline incision a large, lobular, very vascular mobile mass was found (Fig. 3). It originated from the omentum with attachments to the mesentery of the small bowel and the right lobe of the liver. On the surface of the mass there were multiple grossly enlarged (1-2 cm diameter) pulsating arteries and veins, originating from the right gastroepiploic artery and vein and spreading into the gastrocolonic ligament (Fig. 3). The mass was completely removed and the patient made an uneventful recovery. Use of a Ligasure (Fig. 4) for the dissection made it possible to remove the entire tumour with minimum blood loss in a short time; the conventional 'clip and tie' would have taken much longer and resulted in more blood loss in an already anaemic patient.
The surgical specimen was examined and sections were taken for paraffin embedding, as well as processing using the standard haematoxylin and eosin method.
A soft-tissue mass measuring 30 x 24 x 8 cm was attached to the omentum. On the cut surface the mass was soft and haemorrhagic with no areas of necrosis. Cystic spaces containing yellowish fluid alternated with solid areas. Representative sections were taken from the soft-tissue mass.
Many sections were examined and showed solid proliferation of oval to spindle-shaped cells, interspersed by staghorn-type vascular spaces, lined by endothelial cells. No mitosis was present and nuclear atypia was not observed. There were no foci of tumour necrosis.
Sections prepared by the silver impregnation technique showed pericellular deposition of reticulin coarse fibre.
Immunohistochemical examination showed strong positive immunostaining with vimentin as well as bcl-2 (Figs 5 and 6). CD 34 was confined to the endothelium lining the vessels.
Haemangiopericytoma arising from the omentum is extremely rare. [2-11] The primary treatment is surgery, and an R0 excision is preferable. The role of adjuvant chemotherapy or targeted therapy is not well established when there are no demonstrable metastases, in contiguity, lymphatic or haematogenous.
Malignancy can be expected when the tumour is larger than 5 cm, has a high mitotic index and has areas of necrosis. The tumour in our case measured 30 x 24 x 8 cm, but no mitosis or areas of necrosis were found on histological examination; there were also no demonstrable metastases and no residual tumour after removal. We decided not to give the patient any further adjuvant therapy until local or systemic signs of recurrence can be demonstrated. She will be followed up regularly at the surgical outpatient department, where she will be assessed clinically as well as by abdominal ultrasound. CT and magnetic resonance imaging scans will be done if there is any suspicion of recurrence.
Haemangiopericytoma is characterised microscopically by a solid proliferation of oval to spindle-shaped cells that appear cytologically bland, often with vascular arcades interspersed. In some areas, typical staghorn architecture of thin-walled branching vessels is observed. The tumour may exhibit variable degrees of cellularity, and in more cellular areas vessels therefore tend to be small and collapsed and can only be highlighted by reticulin stains. A few cases of aggressive behaviour and even distant metastases have been described. [12-13]
Microscopic criteria often used to predict biological behaviour in primary tumours include the degree of cellularity, the degree of nuclear atypia and the presence of tumour necrosis. [12-13] The presence of distant metastases is unequivocal evidence of malignancy.
Our patient's tumour had huge veins and arteries (1-2 cm in diameter)(Figs 3 and 4) on the surface, and large vascular spaces deeper in the parenchyma (Figs 1 and 2). There is a possibility that microangiopathic haemolysis of red blood cells had taken place.[14The anaemia could be explained by breakdown of red blood cells, as is found in giant haemangiomas. The platelets were normal, and the patient had no stigmata of a consumption coagulopathy as is found in Kasabach-Merritt syndrome.
It is currently considered that the term haemangiopericytoma should be reserved for neuropathologists, and the term solitary fibrous tumour rather than haemangiopericytoma should be favoured by soft-tissue pathologists. The reason for this change in nomenclature is because the staghorn-branching vascular pattern representative of haemangiopericytoma is found in 15% of all soft-tissue tumuors. According to soft-tissue pathologists, the term solid fibrous tumour better describes a rare heterogeneous group of benign and malignant neoplasms along a morphological continuum. [13,15,16]
We report a case of haemangiopericytoma/solitary fibrous tumour of the omentum. This very rare tumour was treated successfully with complete surgical removal. On histological examination it appeared to be benign, except that the size favours malignancy, tumours larger than 5 cm being considered malignant. Our patient had no demonstrable metastases, so it was decided not to provide any adjuvant therapy. She will be closely followed up and investigated for recurrence, local or systemic, the final arbiter for malignancy.
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J H R Becker, (1) MB ChB, MMed (Surg), FCS (SA), FRCS (Edin and Glasg); M Z Koto, (1) MB ChB, FCS (SA); O Y Matsevych, (1) MD (UA); N M Bida, (2) MB ChB, MMed (Path), FFPath (SA), MRCPath, MBA, MPH, Cert Mol Biol
(1) Department of Surgery, Faculty of Health Sciences, School of Medicine, University of Limpopo (Medunsa Campus), Pretoria, South Africa
(2) Department of Histopathology, Faculty of Health Sciences, School of Medicine, University of Limpopo (Medunsa Campus), Pretoria, South Africa
Corresponding author: J H R Becker (email@example.com, firstname.lastname@example.org)
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|Author:||Becker, J.H.R.; Koto, M.Z.; Matsevych, O.Y.; Bida, N.M.|
|Publication:||South African Journal of Surgery|
|Article Type:||Case study|
|Date:||Nov 1, 2014|
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