Calcifying fibrous pseudotumor is a rare, benign, tumorlike lesion that is composed of fibrous tissue with diffuse deposits of calcium and infiltration of inflammatory cells. We report the case of a girl who had such a lesion in the shoulder girdle. Histopathological examination revealed circulatory disturbances, including narrowing of the feeding artery with thickening of the wall, hyalinization of collagen fibers around the capillaries, and thrombi in the capillaries.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Department of Orthopaedic Surgery, Yamagata University School of Medicine, 990-26 Iida-Nishi 2-2-2, Yamagata, Japan.
‡Second Department of Pathology, Tokyo Woman's Medical College, 162 Shinjuku-ku, Kawada-cho 8-1, Tokyo, Japan.
A thirteen-year-old girl was seen in June 1995 because of a mass in the left shoulder girdle that she had first noticed a month before. The patient had been a pitcher for a softball team but had no history of major traumatic injury. She had slight pain with movement and had not noticed any recent increase in the size of the mass. She had a history of congenital dislocation of the hip, but there was no family history of such dislocation. Physical examination revealed a six by six-centimeter, hard, mobile, tender mass between the eminence of the deltoid and the lateral head of the triceps.
Plain radiographs (Fig. 1-A) and computerized tomography scans (Fig. 1-B) revealed a lobular mass. Magnetic resonance images revealed a well demarcated lobular mass between the deltoid and the lateral head of the triceps; the border between the mass and the surrounding muscles was well marginated in most areas but was poorly defined in some areas. On T1-weighted images, the signal intensity of the mass was equal to that of the surrounding muscles, with irregularly striped areas of low signal intensity that were suggestive of calcification (Fig. 2-A). On T2-weighted images, the mass had low signal intensity with irregularly scattered areas of high signal intensity (Fig. 2-B). On T1-weighted images that were enhanced with gadolinium-diethylenetriamine pentaacetic acid, the mass had high signal intensity with irregular focal areas of low signal intensity (Fig. 2-C). Angiography revealed that the posterior circumflex humeral artery branched into several vessels that entered the tumor and surrounding tissues. Some contrast medium that had entered the mass through the artery remained there, producing so-called tumor-staining. No irregularity of the arterial wall or encasement of the artery was detected.
An open biopsy was performed in July 1995, and a piece of white, solid, fibrous tissue was obtained. Histopathological examination of the specimen revealed cicatricial tissue and diffusely distributed calcifications with no evidence of malignancy.
The mass was excised one week after the biopsy. At the time of the excision, the mass was found to be located between the deltoid and triceps muscles and appeared to be extending into them as well. The posterior circumflex humeral artery was completely surrounded by the mass, and some of its branches were spread over the mass. On gross examination, the lesion was found to be a five by six by seven-centimeter, solid, lobular, well circumscribed, non-encapsulated, gray-white mass. The cut surface was gray-white with a gritty texture and a whorled appearance. There was no evidence of infiltration into the deltoid or the lateral head of the triceps.
Histological examination revealed that the mass contained hyalinized fibrosclerotic tissue that was composed mainly of interwoven bundles of collagen with randomly scattered calcifications and a variety of inflammatory cells (Fig. 3-A). The bundles of collagen were often wrinkled like those of a desmoid tumor (Fig. 3-B) and were sometimes whorled to form spherical collagenous nodules. Elastica-Goldner staining revealed no elastic fibers except around the blood vessels. No amyloid deposition was observed on sections stained with Congo red. Two types of calcification—irregular, amorphous dystrophic calcification (Fig. 4-A) and laminated psammomatous calcification (Fig. 4-B)—were observed. Van Kossa staining also showed these two types of calcification. Ultrastructural studies showed the deposition of calcium along the extracellular collagen fibers (Fig. 4-C). A focus of calcification was also found in the fibrous wall of one of the blood vessels. The infiltrating inflammatory cells were composed chiefly of lymphocytes, plasma cells, mast cells, and eosinophils that formed focal lymphoid aggregates. The capillaries often were circumscribed by multiple layers of hyalinized collagen fibers (Fig. 5-A). The intimal and medial layers of the wall of the posterior circumflex humeral artery were thickened, causing narrowing of the canal in the region of the mass (Fig. 5-B). There were occasional thrombi in the capillaries (Fig. 5-C).
Two and a half years after the excision, the patient had no evidence of recurrence or metastasis.
Calcifying fibrous pseudotumor is a rare, benign, tumorlike lesion that is characterized histologically by fibrotic proliferation, infiltration of inflammatory cells, and dystrophic and psammomatous calcifications1,4,7,12,14. As far as we know, Rosenthal and Abdul-Karim were the first to describe this lesion; in 1988, those authors reported on two patients who had what was termed a "childhood fibrous tumor with psammoma bodies." Fetsch et al., in 1993, reported on ten patients who had what was described as a calcifying fibrous pseudotumor. This lesion has also been found in the epididymis and the pleura1,7,12. In 1985, Lee and Sen reported on a patient who had "dystrophic and psammomatous calcifications in a desmoid tumor," which was pathologically similar to the lesion described here and was probably a calcifying fibrous pseudotumor.
There are several similarities between calcifying fibrous pseudotumors and inflammatory pseudotumors, which are generally considered to be reactive lesions10. Like calcifying fibrous pseudotumors, inflammatory pseudotumors always are characterized by fibrotic proliferation and infiltration of inflammatory cells6,10. The lesion described in the present study demonstrated marked infiltration of mast cells. Mast cells are often found in fibrous tissues, such as those of a neurofibroma, and the infiltration of mast cells supposedly is associated with the formation of fibrous tissue. Calcification often is observed even in inflammatory pseudotumors10. Matsubara et al. identified three types of inflammatory pseudotumors of the lung: the organizing pneumonia type, the fibrous histiocytoma type, and the lymphoplasmacytic type. Calcification was observed in association with the fibrous histiocytoma type10. Moreover, pulmonary hyalinizing granulomas have been found to be composed entirely of whorled deposits of lamellar collagen bundles and have been associated with ischemic necrosis and occasionally with calcification15. Such granulomas are thought to be the end stage of inflammatory pseudotumors15. In addition, ischemia is thought to be associated with calcification; in the present report, calcification was found more frequently in hyalinized areas of the mass. These findings support the theory that calcifying fibrous pseudotumors have a reactive origin and that they are within the broad spectrum of inflammatory pseudotumors.
Calcifying fibrous pseudotumors generally show two types of calcification. Dystrophic calcification, which presumably results from direct mineralization of extracellular collagen fibers9, is found in the degenerative collagenous tissues of aortic valves showing age-related changes7 as well as in desmoid tumors9. Psammomatous calcification, which originates in the cytoplasm and is formed by the fusion of calcific bodies that extrude from calcified cells3,11, is found in meningiomas2, ovarian serous tumors3, gastric carcinomas11, tumoral calcinosis13, and desmoid tumors9. In the present study, ultrastructural examination of the biopsy specimen revealed the deposition of calcium along the extracellular collagen fibers as well as intracellular calcification in residual bodies.
The lesion described in the present report also was associated with circulatory disturbances, including narrowing of the feeding artery and capillary thrombi. We propose two possible relationships between such disturbances and the etiology of calcifying fibrous pseudotumors. First, narrowing of the feeding artery may cause ischemia or thrombosis, or both, resulting in inflammation and fibrosis in the muscles. Alternatively, enlargement of the tumor may constrict the feeding artery and capillaries, thereby causing thrombosis.
Although the histological features of the lesion described in the present report were characteristic of a calcifying fibrous pseudotumor, it was difficult to differentiate the mass from a desmoid tumor, especially before the biopsy. The appearance of the mass on magnetic resonance images closely resembled that of a desmoid tumor4,5. On T1-weighted magnetic resonance images, both lesions show irregular areas of low signal intensity and irregular enhancement with gadolinium-diethylenetriamine pentaacetic acid5, whereas on T2-weighted images, they both show low signal intensity intermingled with areas of high signal intensity. Furthermore, the borders between both types of lesions and the surrounding muscles are poorly defined in some areas. These similarities make it difficult to distinguish calcifying fibrous pseudotumors from desmoid tumors.
Calcifying fibrous pseudotumors usually can be distinguished from desmoid tumors on the basis of histopathological features such as the presence of calcification and the infiltration of inflammatory cells. However, we are aware of one report in which a desmoid tumor demonstrated dystrophic and psammomatous calcifications9. Moreover, if the biopsy specimen is obtained from a cellular area of a calcifying fibrous pseudotumor, the histological findings may resemble those of a desmoid tumor because calcification is abundant in hyalinized fibrous areas and scarce in cellular areas. Therefore, the demonstration of infiltration of inflammatory cells may be more helpful for distinguishing calcifying fibrous pseudotumors from desmoid tumors.