Hemangiopericytomas constitute a small subset of soft tissue sarcomas. They were first named by Stout and Murray in 1942, and described as distinct vascular soft tissue tumors characterized by groups of endothelial-lined tubes and sprouts, featuring Zimmerman's pericytes [2, 3]. Only recently, evolving histopathological concepts and the new 2006 WHO classification of soft tissue sarcomas abandoned this previous vision of a pericyte-derived tumor in favor of a fibroblastic cell origin, integrating this lesion into the family of solitary fibrous tumors .
These neoplasms primarily affect adults aged between 20 and 70 years old, with the median age in the 40 s and 50 s. Males and females are affected equally [3–6]. The most common anatomic locations are the lower limbs, axilla, retroperitoneum, pelvic fossa, and head and neck, although hemangiopericytomas have also been described in many other locations such as the lung, breast, peritoneum, liver, pancreas, stomach, greater omentum, mediastinum, bone, inguinal region, uterus, ovary, and vagina . Hemangiopericytomas rarely originate in the spleen as a primary tumor (only ten cases have been described in the international literature), and this presentation was first reported by Guadalajara Jurado et al. in 1989 [8–16]. Splenic hemangiopericytoma is typically asymptomatic and results in splenomegaly. There may be single or multifocal lesions. Given their hypervascular nature, expansive growth, change in the structure of the vessel walls, erosion and necrosis, these lesions can bleed.
Macroscopically, the tumor appears soft and rubbery, and is encapsulated. The average size of such tumors is 6.5 cm . Microscopically, hemangiopericytomas are characterized by well-developed, branching, "stag-horn," thick-walled vessels surrounded by a connective tissue sheath, moderate-to-high cellularity, and a monotonous appearance under light microscopy examination . Imaging studies show a rounded, sharply outlined mass of homogenous density. The typical ultrasonographic picture is a mass with clearly defined margins and a heterogeneous echo pattern that is highly vascularized on color Doppler .
On computed tomography, the lesion appears as a well-demarcated, highly vascularized soft tissue mass that can displace adjacent organs . Cystic areas of low attenuation, consistent with necrosis, calcifications, which are frequent in large lesions, and invasion of surrounding structures can be present and are suggestive of a malignant form. Despite improvements in imaging techniques, the differential diagnosis and management of splenic hemangiopericytoma are problematic because of the rarity of the disease. Staging studies include chest, abdominal, and pelvic computed tomography.
The difficulty of predicting the prognosis and clinical behavior of hemangiopericytomas has been repeatedly stressed in the literature. Certain characteristics of the tumor, such as large size (>5 cm), a high number of mitotic figures (>4 mitoses/10 high-powered field), cellular atypia, presence of necrosis, and/or hemorrhage can help to differentiate the malignant form from the benign form [3, 5]. The reported rate of metastasis varies significantly from 10 to 60% [3, 5, 6, 18, 19]. The pattern of malignant spread is principally hematogenous to the lung, bone, and liver, while lymphatic metastases are uncommon.
Surgical resection, ideally with negative microscopic margins, is the treatment of choice. Local recurrences have been reported in one-third of patients . Oncological treatment standards are hampered by organotropic hemangiopericytomas that mimic benign forms or require emergency operations for bleeding. Radiotherapy reduces local recurrences, as shown for other soft tissue sarcomas, while the role of adjuvant chemotherapy is controversial. The management of local recurrences and metastatic disease is challenging, because no clearly effective therapy exists. In particular, hemangiopericytoma originating in the abdomen behaves aggressively and a careful, life-long follow-up is required for patients because recurrence and metastases can develop after an extended disease-free period.
Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.