A Case of a Chronic Expanding Hematoma Caused by an Epidermal Cyst

Summary:

Chronic expanding hematoma (CEH) is a rare type of hematoma that expands slowly and continuously without compromising coagulation. Its etiology is often unknown. However, we experienced a rare case of CEH, in which an epidermal cyst was thought to be the cause. A 57-year-old man had developed a painless soft-tissue tumor in his left buttock 45 years earlier, which slowly grew to 11 cm in diameter. Preoperative magnetic resonance imaging suggested a large cyst containing several masses. Surgery revealed a hematoma and keratin debris surrounded by a white fibrous cyst wall and a fibrous nodule measuring 4 cm in diameter. On histopathological examination of the white fibrous wall, an epidermal component was observed contralateral to the superficial punctum, but the epidermal component was absent from most of the wall, including the fibrous nodule. Based on a pathological examination, the CEH was suggested to have been caused by partial rupturing and inflammation of an epidermal cyst. To the best of our knowledge, there are no reports of epidermal cysts causing CEH. In addition, the large fibrous nodule protruding from the CEH cyst wall was considered to be rare. This was considered to be a rare CEH that may have originated from an epidermal cyst.

Epidermal cysts are common keratin-filled epithelial tissue-lined cystic lesions, which may occur anywhere, although they most frequently affect the head and face. They arise in the dermis or subcutaneous tissue as a movable nodule with a central punctum.¹

On the other hand, chronic expanding hematoma (CEH) is a rare type of hematoma that slowly and continuously enlarges.² The specific mechanism underlying its enlargement is not completely understood. A typical CEH is a simple oval hematoma caused by trauma or surgery adjacent to a fascia in a lower extremity or buttock. We encountered a CEH containing keratin debris and a large fibrous nodule (diameter: 4 cm). Based on a pathological examination, the CEH was considered to have been caused by partial rupturing and inflammation of an epidermal cyst.

PATIENT

The case was a 57-year-old man who, according to his description, had developed a painless soft-tissue tumor about 2 cm in diameter on his left buttock for about 45 years, which had grown gradually. There was no history of related surgery or trauma. He had not been taking anticoagulants drugs. A blood examination revealed no anemia, platelet count 29 × 10⁴ per µL, prothrombin time (PT) of 14.2 seconds (9.8–12.1), a PT-international normalized ratio of 1.13 (0.90–1.15), and an activated partial thromboplastin time of 28.6 seconds (24–32). A physical examination showed a mass of 11 cm in diameter with capillaries and a central punctum expanding on the surface of his left buttock. Magnetic resonance imaging (MRI) revealed a fluid-containing cystic lesion (diameter: 11 cm) with smooth edges and sharp boundaries in the left buttock (Fig. 1). There were at least three solid lesions within the cystic lesion (Fig. 2). Although this was an atypical finding, a benign epidermal cyst was suspected and resected under general anesthesia. The entire mass was excised without rupturing. The cystic tumor showed a thin white fibrous wall, containing relatively serous dark brown fluid and keratin-like debris. Two of the three solid areas seen within the cystic tumor on MRI were keratin residues; the third was a fibrous nodule, 4 cm in diameter, attached to the wall, and protruding medially (Fig. 3 〇). For the flap-like wound after tumor resection, quilting sutures were applied to the subcutaneous layer, and a negative pressure suction drain was used so as not to create a dead space. It healed uneventfully, and the patient did not have any problems with sitting.

Fig. 1.

Preoperative image. A mass (diameter: 11 cm) containing capillaries was expanding, and a central punctum had formed on the surface of the left buttock.

Fig. 2.

MRI T2-weighted image. A cyst with a diameter of 11 cm was seen. The fluid contents showed high signal intensity. There were at least three solid lesions inside the cyst. ○ and △ are explained in the legends of Figures 3 and 4.

Fig. 3.

Interior of the cyst with a thin white fibrous wall. In the subsequent pathological examination, a small area of epithelial components was observed in the cyst near the surface punctum (△). A fibrous nodule of 4 cm in diameter was seen on the opposite side (○).

A histopathological examination showed that the cyst wall was composed of a fibrous stroma and had encased clumps of old red blood cells. A small area of epithelial components was observed in the tumor near the punctum (Fig. 4). The 4-cm nodule was also composed of a fibrous stroma. [See figure, Supplemental Digital Content 1, which displays hematoxylin and eosin staining (magnification: 10×). Edge of the fibrous nodule measuring 4 cm in diameter. This region was composed of fibrous stroma. No epidermal components were found. http://links.lww.com/PRSGO/C653]. There were no obvious areas of vasodilation in the fibrous wall that could have caused bleeding. We diagnosed the tumor as a CEH.

Fig. 4.

Hematoxylin and eosin staining (magnification: 10×). △ site in Figure 2: Skin surface near the punctum (upper-most portion) and the cyst wall. Within the cyst wall, epidermal cells and keratin debris were seen.

DISCUSSION

We initially suspected that the tumor was a large epidermal cyst because it grew over a very long period, and the surface punctum was in an appropriate position. Although the incidence of sarcoma has been reported to be low (1% of all malignancies),³ we performed MRI to rule it out and to rule out a hemangioma or a synovial cyst derived from the ischium. A blood examination revealed a slightly prolonged PT (14.2 seconds). There was no other disease, including liver disease. Recently, CEH was shown to be a cause of disseminated intravascular coagulation.⁴ Although the patient did not have anemia and his platelet count was normal, slightly prolonged PT could be attributed to CEH. Unfortunately, no posttreatment blood samples were taken.

The tumor contained serous dark brown fluid within a cyst wall composed of fibrous stroma and slowly expanded. On histological examination, clumps of old red blood cells were found in the cyst wall. Based on this finding, we diagnosed the tumor as a CEH. On the other hand, in the fibrous cyst wall, an epithelial component was observed on the opposite side to the punctum, and preoperative MRI showed what was subsequently revealed to be keratin debris at this site (Fig. 2 △). Based on these observations, we consider that the CEH was derived from an epidermal cyst.

Moreover, the CEH was accompanied by a large fibrous nodule, measuring 4 cm in diameter, in the fibrous wall. A case of an epidermal cyst in the gluteal region that exhibited similar fibrous wall thickening and luminal ulceration has been reported.⁵ In the latter case, the thickened fibrous wall was presumed to have originated from a keratin granuloma. The size of the lesion was not mentioned. We consider that our case was caused by the same very common mechanism.^1,6,7 However, our fibrous nodule was large, and there have not been any reports of similar cases; so, we consider such lesions to be rare.

In the present case, no large blood vessels were found during the surgical or pathological examinations, and hence, it is not known where the bleeding originated from, but it is suspected that it occurred from the ulcered cystic wall. It is now speculated that the patient’s hematoma formed in four stages.

In the first stage, an epidermal cyst developed. In the second stage, partial rupturing of the epidermal cyst occurred, and keratin-induced inflammation occurred in the ulcerated cyst wall, forming a large keratin granuloma. In general, such lesions often break through the epidermis and are discharged to the outside. However, it was thought that the skin did not break in this case. In the third stage, the large keratin granuloma was replaced by stroma over time. In the fourth stage, keratin excretion from the remaining epidermal cells continued to cause inflammation, and the continued bleeding from the ulcerated cyst wall caused the CEH.

Because the hematoma occurred near the ischial bone in the left buttock, it was considered that chronic stimulation from sitting caused each stage to progress. It is not known when the partial rupturing and hematoma formation occurred because the patient was unaware of them.

To the best of our knowledge, there are no reports of epidermal cysts causing CEH. In addition, the large fibrous nodule protruding from the fibrous cyst wall was also considered to be rare. This rare CEH was considered to have originated from an epidermal cyst.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.

ACKNOWLEDGMENTS

This report was based on the course of treatment of the patient in accordance with the Declaration of Helsinki. The treatment for this patient is within the scope of medical insurance coverage in Japan and does not include experimental elements.

Supplementary Material

gox-11-e5116-s001.pdf ^{(2.2MB, pdf)}