Angiosarcomas are extremely high grade malignant neoplasms, which account for 2% of all soft tissue sarcomas and of which, primary renal angiosarcomas represent about 1%. Only 24 confirmed cases have been published in the literature so far(1). Angiosarcomas can present with various grades of differentiation, and originate from the endothelium of the blood vessels and lymphatics. They are usually diagnosed as renal cell carcinoma due to a similarity in radiological appearances , and the accurate diagnosis is usually made through histology and immunohistochemical findings. Histologically, the tumors have numerous blood-filled vascular spaces which are lined by plump pleomorphic endothelial cells with CD31 and CD34 staining positivity.

Primary renal angiosarcomas are more frequent in white males, between 60 and 70 years of age.

The patients typically present with macroscopic hematuria (81%), flank pain (38%) and a palpable renal mass (31%).

Patients with renal angiosarcoma have a mean survival of about 8 months with most important prognostic factors being tumor size and the presence or absence of metastasis. The prognosis of renal angiosarcoma is uniformly fatal with widespread metastases, and the World Heath Organization reported a mean survival of 7.7 months (2). Metastases were found mainly in the lungs, liver, and bones. Leggio et al. (3) and (4) reported that the most important factor determining the prognosis of renal angiosarcoma in many studies seemed to be the size of the initial lesion. Tumors <5 cm in diameter have a significantly better prognosis than larger lesions. (5, 6, 7). Angiosarcoma of the kidney is a highly malignant tumor, and there seems to be no standard therapy. Radical nephrectomy is the most effective mode of management.

Imaging findings:

Computed tomography (CT):

A dedicated imaging protocol is needed for optimized evaluation of the renal mass by CT. CT scan dedicated for evaluation of a renal mass typically consists of three imaging series performed during breath hold: precontrast, corticomedullary phase, and late nephrographic/early excretory phase (8, 9, 10 ). Precontrast images are essential for evaluation of the presence of calcifications and provide a baseline density measurement for evaluating the degree and pattern of enhancement in cystic or solid renal masses (10). Cortico-medullary phase (typical scan delay 70–85 seconds after injection) is  superior in the assessment of lesion vascularity, renal vascular anatomy, and tumor involvement of venous structures (10). In addition, it is probably the most informative phase for lesion characterization. A relatively thin slice thickness of 2.5 mm may be obtained through the kidneys. To minimize radiation exposure, a standard slice thickness of 5 mm may be obtained through the rest of the body if such imaging is to be performed in the same setting. The most commonly detected malignancy is renal cell carcinoma (RCC). In contrast to RCC, renal sarcomas are often extremely exophytic, displacing, distorting, or compressing the renal parenchyma without parenchymal invasion; as a result, there is often a smooth interface between the tumor and the renal parenchyma (11, 12). Renal sarcomas that do arise within the renal parenchyma are difficult to distinguish from the more common renal cortical tumors, however. On CT, renal sarcomas are typically large heterogeneous exophytic soft tissue masses with areas of necrosis. In contrast to RCC, renal sarcomas do not tend to invade the renal vein or inferior vena cava (11).

Magnetic Resonance Imaging (MRI)

MRI has many advantages over other modalities in the detection and staging of renal neoplasms, owing to its intrinsic high soft tissue contrast, direct multiplanar imaging capabilities, and availability of a non-nephrotoxic, renally excreted contrast agent . Solid renal tumors are typically isointense or slightly hypointense on T1-weighted images. MR imaging is useful in the detection and differentiation of cystic and solid renal lesions (13) with accuracy comparable or superior to that of CT (14)

Ultrasonography (US)

US is an important problem-solving tool for evaluation of renal masses. One of the most important roles of ultrasound is in the characterization of renal lesions as cystic or solid. Because the diagnosis of a simple renal cyst denotes benignity, strict criteria need to be adhered to. The lesion must be completely anechoic, have a thin imperceptible wall, have posterior enhancement, have a round or oval shape, and be avascular. Rarely, a benign cyst can become complex in the setting of hemorrhage or infection and could mimic a solid lesion. Cysts that do not fulfill all of the criteria of a simple cyst are complex, and the possibility of a cystic renal carcinoma may need to be considered depending on a cyst's radiographic features. Presence of internal vascularity within a septa or a mural nodule raises suspicion for malignancy.  Correlation with other imaging modalities, such as CT and MRI, is recommended for confirmation of an enhancing septa or nodule which makes it suspicious for a malignancy.

Summary

CT is the imaging modality of choice for evaluation of renal tumor. When a proper technique is used, CT provides high accuracy in detection of a renal mass. Certain imaging features and enhancement patterns on CT may help distinguish different subtypes of renal tumors. In addition, CT provides useful diagnostic information for treatment planning and follow-up. MR imaging and ultrasound function as valuable problem-solving tools.