Chronic expanding hematoma showing fluid-fluid level.

Sir,

Chronic expanding hematoma is a rare hematoma, which increases in size for more than 1 month,[1] and only two cases showing a fluid–fluid level has been reported. Here, we present a case of chronic expanding hematoma showing a fluid–fluid level on magnetic resonance imaging (MRI) and review of the literature.

A 72-year-old Japanese woman noticed a subcutaneous mass on her left buttock 2 months before. The mass increased gradually, and she felt discomfort when sitting. She had a medical history of chronic renal failure and angina pectoris, having been treated with dialysis and anticoagulant medication of warfarin at 1.75 mg/day and aspirin at 100 mg/day. Prothrombin time-international normalized ratio (PT-INR) was 1.31. Other blood coagulation test results were within normal limits. She did not remember any history of trauma at the site. Physical examination showed a well-circumscribed, hard subcutaneous mass without fluctuation in the ischium region, measuring 6 cm [Figure 1a]. MRI was performed in a prone position. On a T2-weighted sequence, well-circumscribed cystic lesions with two locules were found in the subcutis of her buttocks, and did not adhere to the gluteus maximus. A fluid–fluid level was clearly observed inside the cyst [Figure 1b]. On a T1-weighted sequence, the cyst's central portion showed heterogenous high to intermediate signal intensities. The lesions had an outer rind showing a low signal intensity on T1- and T2-weighted sequences. Complete surgical excision was performed under general anesthesia. The resected lesion resembled a well-circumscribed cyst with a fibrous, hard pseudocapsule and two locules [Figure 1c]. Histopathological examination revealed a cystic structure with a fibrous pseudocapsule, which contained red blood cells [Figure 1d]. No neoplasm findings were observed. We diagnosed this patient with chronic expanding hematoma, and no recurrence has been observed with the continuation of anticoagulant medication.

Figure 1

(a) A well-circumscribed subcutaneous mass, measuring 6 cm, on patient's left buttock; (b) T2-weighted magnetic resonance imaging. A fluid–fluid level was clearly observed; (c) the resected mass. A cystic mass with pseudocapsule; (d) histopathological findings (hematoxylin and eosin, low magnification). A pseudocapsule containing red blood cells with a fibrous wall

The etiology of chronic expanding hematoma remains unclear. It was suggested that the increase of osmotic pressure through deposition of blood breakdown products and its irritant effect should cause permeability change of adjacent vessels.[2] Although our patient took anticoagulant treatment, it has been reported that one third of patients with chronic expanding hematoma had no history of surgery, trauma, or coagulopathy.[3] Coagulation abnormality including anticoagulant treatment does not seem to be essential for chronic expanding hematoma formation.

A fluid–fluid level is formed when substances of differing densities are contained within a cystic structure. It is observed in a wide range of soft tissue tumors,[4] however, it is extremely rare as for chronic expanding hematoma and is speculated to result from the sedimentation of cellular blood components.[4] Only two cases of chronic expanding hematoma showing a fluid–fluid level on MRI were reported in the English literature.[45] We reviewed both cases including our case [Table 1]. The age, gender, size, and duration varied, and anticoagulant treatment was received only by the present case. All affected sites were thought to be easily stimulated, being the only common feature. Intermittent stimulation of chronic expanding hematoma may cause old hematoma and fresh bleeding, which leads to the finding of fluid–fluid level.

Table 1

Chronic expanding hematoma showing fluid-fluid level on MRI: Review of the literature