Primary Omentum Malignant Hemangiopericytoma Present with Acute Abdomen

Introduction

Primary omental malignancies include liposarcoma, hemangiopericytoma, fibrosarcoma, leiomyosarcoma, mesothelioma, desmoid tumor, and malignant fibrous histiocytoma. They are rare, making their diagnosis quite challenging. They are usually found in people in their 50s or 60s.^1,2

In 1942 Stout and Murray described hemangiopericytoma as a distinctive soft tissue neoplasm. Hemangiopericytoma is a type of tumor thought to come from Zimmerman pericytes displaying signs of myoid or myofibroblast differentiation.^3–5 The World Health Organization has classified hemangiopericytoma as a solitary fibrous tumor (SFT) that occurs outside the pleura as either benign or malignant with an overall incidence of 0.6%. While there have been twenty documented instances of hemangiopericytoma, the literature only mentions four cases of hemangiopericytoma.^2,6

Case Presentation

A woman aged 38 arrived at the emergency department of our hospital with symptoms including abdominal pain, constipation, vomiting, and abdominal distension. These symptoms had started three days earlier. However, the patient had a history of abdominal discomfort and distension due to swelling that began in the epigastric area five years earlier. As the patient lives far away, the patient had been taking pain relievers on her own after going to a peripheral rural clinic for assistance. During our examination the patient was fully conscious but seemed unwell and dehydrated. A mass was discovered across the lower half of her abdomen, causing abdominal distention. The mass measured 20×20 cm in size and was hard, non-pulsatile, and tender to palpation. It disappeared when the patient raised her head against resistance and was mobile. The laboratory result complete blood counted HP 7,5 WBC 14. An abdominal ultrasound revealed a large, pelvic-abdominal, heterogeneous, hypoechoic, and highly vascularized soft tissue mass measuring 20×18×10 cm in size, showing high blood flow on color Doppler study. Multiple tortuous, dilated blood vessels with mild to moderate free fluid were also detected in the peritoneal cavity. After receiving intravenous fluids containing ranger lactate, the patient underwent an abdominal CT scan with IV contrast. The results of the scan revealed a clear, large, well-defined, heterogeneous soft tissue mass lesion measuring 20×16×9 cm, found in the lower abdomen and pelvis. These findings were similar to those of a gastrointestinal stromal tumor (GIST) or desmoid tumor [Figure 1].

Figure 1 Abdominal CT scan with IV contrast, revealing a large, well-defined, heterogeneous soft tissue mass lesion measuring 20×16×9 cm, in the lower abdomen and pelvis.

As the patient had an acute abdomen, we decided on exploration laparotomy. During the surgery, a large mass was discovered that infiltrated the greater omentum, measuring about 20×20×10 cm and weighing 3 kg. The mass was close to and compressing the small bowel loops and was associated with mild ascites. There was also free blood in the peritoneal cavity. The mass, along with the omentum, was completely excised and sent for histopathology, while also ensuring a safe margin was maintained during the excision [Figure 2].

Figure 2 During the surgery, a large mass was discovered that infiltrated the greater omentum.

The patient was discharged four days after the operation with good general condition. However, the histopathology results revealed that the mass under the microscope was a tumor growth formed of a sheet of spindle cells having oval-shaped nuclei and an eosinophilic to clear cytoplasm, with foci of moderate nuclear atypia and foci of necrosis also seen. Also noted was separate omental fatty tissue, showing patchy mild mixed inflammation. Mitotic figures were not encountered, and the examination of the immunoassayed section showed the following: CD34, diffuse positive; CD99, weak positive; CD117 and Dog-1, negative; ki67, low proliferation index less than 1%; and SMA, DESMIN, S-100.STAT6 CD31, D2-40, HMB-45, ER, MDM2CDK4, and Bc12, negative. The result of analysis was that the tumor is a malignant hemangiopericytoma. Therefore, the patient was referred to an oncology center for further follow-up.

Discussion

Primary benign hemangiopericytomas of the omentum make up a fraction less than 2% of all soft tissue tumors, while malignant hemangiopericytomas constitute less than 1% of all hemangiopericytomas.^4,7 There have been only four instances recorded of this condition [Table 1]. In hemangiopericytoma cells it is uncommon to find markers, such as desmin and actin, which makes immunohistochemistry not always a reliable diagnostic tool.⁵ On the other hand, hemangiopericytoma cells express antigens such as CD34 (100%), CD99, and Bcl-2 (70–90%).^1,4,8 STAT6 serves as a reliable immunohistochemical indicator for diagnostic purposes,⁹ but in our case CD34 was present, whereas STAT6 was not present. In order to identify hemangiopericytoma it is essential to conduct an assessment including running necessary laboratory tests and carrying out imaging studies.¹⁰ Magnetic resonance imaging (MRI) is a more effective tool than using a computer tomographic (CT) scan to assess the size of the tumor and how it interacts with tissues. In our case, we proceeded with the surgery after reviewing the CT scan results as the size of the lesion necessitated surgery due to rupture of tumor with intra-peritoneal bleeding regardless of the result of tumor type. Additionally, our hospital is currently experiencing resource constraints, and many patients are unable to afford extra investigations.

Table 1 The Five Cases Recorded with This Condition

The vascular tumor under consideration necessitates a treatment regimen that involves surgical intervention, chemotherapy, and radiotherapy to achieve good outcomes.

The primary method of treatment is en-bloc surgical excision¹¹ When surgery is not feasible, radiotherapy is often the option. According to the literature, there is not support for the use of adjuvant chemotherapy.^10,1213 Before proceeding with surgery, it is advisable to conduct a CT or ultrasound-guided biopsy along with staining for diagnosis and treatment. This aids not only in confirming the diagnosis, but also in comprehending the dimensions and prognosis of the mass.^10,14,15

Conclusion

This report describes a rare case of primary omental malignant hemangiopericytoma with acute abdomen. The surgery to remove the tumor only effected part of management. Early detection is important with this kind of tumor, for early surgical intervention, and to improve the prognosis.