CEH is a type of hematoma that is most commonly caused by trauma, and has certain other etiologies such as hemorrhagic disorder. Hematomas are often reabsorbed, and gradually decrease in size. However, in rare cases, they may develop slowly and expand progressively over a period of time. In certain cases, CEH may persist and increase in size for more than 1 month after the initial hemorrhagic event [1
]. Hematomas in the skeletal muscles or surrounding tissue may develop as a result of a direct shearing force that splits the subcutaneous fat from the underlying fascia, thus potentially creating a large space, which may then fill with blood. Labadie et al. [3
] reported that blood and erythrocyte degradation products, hemoglobin, leukocytes, platelets, and fibrin exert an irritant effect on the surrounding tissue. These factors are believed to induce a mild inflammatory response, which increases vascular wall permeability and bleeding from dilated capillaries in the granulation tissue beneath the capsular wall, thus resulting in the subsequent growth of the hematoma. However, no trigger such as trauma or anticoagulant therapy was identified in the present case.
Careful examination of a PubMed database search of articles published from 1970 to 2012 using the key words “chronic expanding hematoma” yielded 204 cases of CEH. Of these 204 cases, 79 cases were detected in the brain and spine; 59 were detected in the thorax; 56 were detected in subcutaneous tissues and muscles of the arms and legs; and 10 were detected in the abdomen, of which 7 were located in the retroperitoneal space (Table ) [1
]. None of the cases listed above presented with hydronephrosis. In the present case, the unusual size of the retroperitoneal lesion may have resulted in compression of the left ureter and kidney.
Reported cases of retropritoneal chronic expanding hematomas
CEH may be difficult to differentiate from soft tissue tumors (such as hemangiopericytomas and cavernous hemangiomas), sarcomas, actinomycosis, and inflammatory pseudotumors [7
]. Weiss et al. [8
] reported that hematomas are associated with approximately 5% of malignant fibrous histiocytomas.
Various imaging modalities have been used for the diagnosis of CEH. It has been stated that a dynamic CT scanning can detect a rim enhancement in the arterial phase in such cases, because granulation tissue with vascular channels is distributed within the hematoma capsule [2
]. In the present case, enhanced CT revealed a partly enhanced rim. Although MRI is inferior to CT in identifying calcification or spatial resolution, MRI is more sensitive than CT in the diagnosis of hematomas. The signal within the lesion on MRI can vary with the passage of time, indicating time-related changes in hemoglobin levels. High signal intensity on T1-weighted images are attributable to the presence of methemoglobin within the hematoma. A few soft tissue tumors such as lipomas, liposarcomas, and hemangiomas also yield enhanced high signal intensity on T1-weighted images. However, it can be difficult to differentiate hematomas from malignant soft tissue tumors based on clinical and radiological findings because of the time-related changes in MRI signals [10
]. Liu et al. reported that CEH should be considered in the differential diagnosis for soft tissue masses that exhibit internal hemorrhage and fibrous pseudocapsule during unenhanced T1- and T2-weighted MRI. If the contrast enhancement is patchy within the lesion, a diagnosis of hemorrhagic sarcomas should be considered [11
]. In the present case, high signal intensity was predominantly observed on both T1-and T2-weighted images, except for an area of low signal intensity that represented a wall of collagenous fibrous tissue on the peripheral rim. A T2-weighted image of MRI in the present case showed a “mosaic sign,” which meant that the lesion involved repeated bleeding because it contained a mosaic of various signal intensities representing fresh and old blood [12
]. These atypical MRI findings indicated the presence of CEH.
The optimal treatment option for CEH is complete excision of the hematoma together with its fibrous capsule. Aspiration of the liquid or drainage could result in serious bleeding or recurrence [9
]. However, hematomas are often difficult to remove because of adhesion to the surrounding tissue and abundant neovascularization beneath the capsule. By using CT in particular, the presence of new capillaries and granulation tissue can be easily identified if contrast material is used [9
In the present case, the left kidney was hydronephrotic. Therefore, a double J-stent was placed in the left ureter to aid in identifying and preventing injury to the left ureter. The double J-stent was removed 2 months postoperatively, and the hydronephrosis in the left kidney had resolved. To our knowledge, a hematoma of a comparable size as the one reported in the present case, accompanied with left hydronephrosis, has never been reported in the literature. Moreover, in the present case, the etiology of CEH was unclear and could not be determined during surgery. Although no recurrence was evident at the 2-year follow-up, it is essential to further follow-up the patient carefully.