The Significance of Growing Bone Islands

Abstract

LITTLE INFORMATION concerning the etiology and significance of compact bone islands is available in the radiological literature or standard reference texts. This may simply reflect the ease with which these small structures may be differentiated from other bony abnormalities. Indeed the major importance of recognizing bone islands lies in the need to distinguish them from significant pathological processes. The concept that bone islands may grow in size and density, simulating osteoblastic metastases, has not received significant support. It is the purpose of this paper to focus on this concept, and to present evidence that bone islands may increase strikingly in size over a period of years. Material Case histories were gathered from the material of the in-patient and out-patient services of a 1,000-bed general medical and surgical facility where the vast majority of patients were male. Out of a large number of examinations performed over approximately five years time, the cases were culled by scrutiny of films during interpretation and careful comparison with previous examinations whenever obtainable. In no way does the material reflect the incidence of growing bone islands. In 6 cases, unequivocal evidence of growth of bone islands was detected. The intervals over which expansion in size and density occurred varied from two to fourteen years. In one case, which is presented, the pathologic diagnosis of the true nature of the bone island was also available. Three of the others for which histological proof was lacking were chosen to serve as additional illustrations. As the legends accompanying the illustrations indicate, these last-named patients were being followed for a variety of clinical problems. Case Report Case I: A 64-year-old male was subjected to a transurethral resection of the prostate in 1956 for benign prostatic hypertrophy. He was admitted to the hospital in 1961 because of a urethral stricture. Films obtained during the course of intravenous pyelography showed a few focal areas of sclerosis in the iliac bones and sacrum. On comparison with the films dating back to 1956, these appeared unchanged, except for the lesion near the right iliac crest (Fig. 1). This had increased from 9 mm in diameter in 1956 to 14 mm in 1961. Nevertheless, it was thought to represent a benign bone island. Because of its easy accessibility and the clinician's concern that an osteoblastic metastasis be excluded, the lesion was removed. Gross and microscopic sections confirmed the diagnosis of benign bone island (Fig. 2). Discussion In 1905, Stieda observed that roentgen-ograms demonstrated small, circumscribed, dense, oval shadows inside the cancellous structure of short bones or the epiphyses of long bones (8). Because of their frequency, it was felt they were not pathological but were variants of normal.