Bone Cysts

Abstract

IN the differential diagnosis of the pathologic conditions affecting organs or tissues, there is often one condition around which center most of the difficulties of the problem. In the mammary gland, cystic mastitis or fibro-epithelial degeneration, because of its clinical varieties and unknown possibilities, seems to occupy this position. In bone, osteitis fibrosa, occupying a mid-position between neoplasm and inflammation, causes, at times, a good deal of confusion. Because of the frequent presence of cyst formation in this disease, perhaps the subject of bone cyst formation has been associated more often in our minds with osteitis fibrosa than with any other one pathologic condition of bone. It is important, however, to remember when we are facing the problem of differential diagnosis the various conditions of bone in which cyst formation occurs. (1) As degeneration product of a solid tumor, (2) As a parasitic cyst, (3) As the end-product of an infectious osteomyelitis, (4) As the product of rarefying process in bone, e.g., arthritis deformans, in osteoporosis, and in osteomalacia, (5) Rickets, (6) Callus cysts, (7) Osteitis fibrosa. After a consideration of all of these causes of bone cyst, there remains the genuine simple bone cyst, which, perhaps, has nothing to do with any of the conditions named. This simple cyst is found most frequently in youth; is usually a single cavity, although at times divided by septa; has a smooth wall provided with a definite limiting membrane, and contains a yellowish, slimy, and occasionally a blood-tinged fluid. It is most frequently found in the metaphyseal region of the shaft of the long bones. A cyst conforming to this description is always a benign lesion. The following case, seen clinically over a period of twenty-five years, can fairly be classified as a genuine simple bone cyst. The patient, a girl of 5 years, gave a history of injury, with an immediate swelling which gradually increased in size. This history, however, could be interpreted in two ways, either as an etiologic factor, or—and this seemed more likely—an injury to an existing condition. She presented a swelling of the upper end of the ulna, which was neither painful nor tender. Pressure over this area resulted in a parchment crackling, characteristic of bodies with thin, more or less elastic walls, such as is felt most clearly on indenting a tennis ball. When this was first seen it presented an appearance as shown in Figure 1. For a time there was a steady increase in size and then a gradual decrease, extending over a period of years, until, at the present writing, there is a barely perceptible difference in the ulna of the two forearms. The radiograph, however, reveals that the bone at the site of the cyst is still very slightly larger than the opposite one (Figs. 2-A and 2-B), the trabecular markings somewhat coarser, and an area about the size of a small pea, which resembles a small cavity, is seen.