Contrast-enhanced ultrasound (CEUS) revealed a hypoechoic mass of 9.8 × 8 × 11 cm with an irregular and heterogeneous structure and abundant vascularization. Having not excluded in our differential diagnosis an abscess formation, paracentesis was performed which revealed pus with abundant pyospheres and a negative culture. A wide drainage procedure was decided on, and sticky material was encountered along with extensive bleeding from the tumor site. Biopsy material was sent for pathological examination. Postoperatively, there was no clinical and biochemical improvement and our patient remained distressed, despite the use of wide spectrum intravenous antibiotics.

Abdominal CT scan was performed, and the report led to the diagnosis of a paraspinal abscess formation (fig. ​(fig.1).1). Under ultrasound guidance, percutaneous drainage was attempted unsuccessfully due to the thick consistency of the tumor content. A repeat ultrasound examination showed pronounced vascularization inside an ill-defined structure with contrast material oozing from the paracentesis site, thus a sarcoma was suspected by the radiologists.

At that time, we obtained the biopsy results that showed malignant fibrous histiocytoma of inflammatory type. Immunohistochemistry revealed positive reactivity to CD68 and vimentin and negative reactivity to CKAE1, CKAE3, EMA, CD45, CD15, CD30, S100, HMB45, MELAN-A, actin, desmin, MVOD1, CD34, CD99, chromogranin, and synaptophysin (fig. ​(fig.2).2). Our patient was scheduled for magnetic resonance imaging, which showed a large heterogeneous space-occupying lesion with lobular peripheral architecture at the anatomical site of the right sacrospinalis muscle, with signs of malignant infiltration of the right iliac bone (fig. ​(fig.33).

After an oncological consultation meeting, the tumor was considered inoperable and the patient was scheduled for neoadjuvant radiotherapy. Unfortunately, excessive bleeding occurred that required multiple transfusions. Finally, our patient died 5 months after the initial presentation of the disease.

Patients with retroperitoneal tumors develop constitutional symptoms including malaise, weight loss, anorexia, and abdominal discomfort. Apart from these symptoms, patients suffering from inflammatory MFH tumors present with fever, leukocytosis with neutrophilic or eosinophilic predomination and elevated serum C-reactive protein [5]. Thus, it is not unusual to consider an abscess formation in the differential diagnosis, as in our case. Some studies have documented that inflammatory MFHs have eosinophilic and neutrophilic chemotactic activity, which could potentially explain the blood chemistry profile and the abundant neutrophil infiltration of the tumor [6]. There are an increasing number of reports that implicate an association of accidental or surgical trauma and the pathogenesis of MFH [7]. This hypothesis applies to our case, since our patient had reported a recent fall at the site of the tumor. We believe that trauma plays an important role in the development of MFH, but further studies are needed for clarification.

Imaging modalities are helpful in providing data about the size, location, vasculature, extension of the tumor, and in designing preoperatively the extent of the surgical excision. Inflammatory MFH quite often present as well-defined lesions, with hypoechoic features, with or without intralesional calcifications at abdominal real-time ultrasound scanning [8]. Computer tomography scanning with intravenous contrast agents shows muscle density patterns, and, as occurred in our case, these tumors are mostly hypervascular with an early wash-out venous phase [9], even though less frequently, these tumors might be hypovascular due to tissue necrosis and hemorrhage [10]. Magnetic resonance imaging has not proved helpful in distinguishing between benign and malignant lesions. De Schepper et al. [11] found that the signs that had the greatest specificity and sensitivity for malignancy included ‘absence of low signal intensity on T2’, ‘signal inhomogeneity on T1’, and ‘mean diameter of the lesion greater than 33 mm’. Kalayanarooj [12] concluded that features that favor malignancy with statistical significance were heterogeneous signal on T2-weighted, perilesional edema or invasion, and necrosis in the masses. Definitive diagnosis can be made only by biopsy, which should be taken at multiple sites to avoid misdiagnosis [4].