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© 1996 The Journal of Bone and Joint Surgery, Inc. Osteoma of the Long Bones and the Spine. A Study of Eleven Patients and a Review of the Literature*  , CLEVELAND, OHIOInvestigation performed at the Departments of Orthopaedics and Pathology, University Hospitals of Cleveland, Cleveland
The clinical features, radiographic and histopathological findings, treatment, and results are described for eleven patients who were managed for an extracranial osteoma at our medical center between 1980 and 1993. Ten of the patients were initially seen because of dull, aching bone pain that had been present for two weeks to thirty years. Radiographs demonstrated single or multiple homogeneous, well defined, radiodense foci with smooth round or lobulated margins. The histopathological features consistently included uniformly dense, compact, cortical-like, mature lamellar bone. The preoperative diagnosis was unclear for all patients, and osteoma was rarely considered in the differential diagnosis. For four patients, a tentative diagnosis of osteosarcoma was made, and a wide excision was carried out in two of these patients. Marginal excision with less than three millimeters of normal tissue around the lesion was performed in most patients. None of the osteomas recurred, and ten patients had relief of the pain. Awareness of the clinical, radiographic, and histopathological features of osteoma, as described, is valuable for making a differential diagnosis and for distinguishing osteomas from other lesions.
Osteomas are rare, slow-growing lesions composed of compact bone12 that occur almost exclusively in the skull8,14, most often in the inner and outer table of the calvarium or in the bones of the face or mandible2,4,6,7,18,19. The prevalence has been estimated to be 4.2 (0.42 per cent) of 1000 patients who have had sinus radiographs18. Although these lesions may cause sinusitis or exophthalmus when they arise from the wall of the nasal sinuses or the orbit, cranial osteomas often cause no symptoms and are discovered incidentally. Primary extracranial osteomas are extremely rare, with a prevalence of 0.03 per cent of 1000 patients who have a biopsy of a primary bone tumor14. Most of these extracranial lesions are multiple, and—when associated with colonic polyps, fibromatoses, and cutaneous cysts—they constitute Gardner syndrome. There have been only a few reports of non-syndromal extracranial osteomas in the long bones4,6,7,13,18-20 or the pelvis5,15. In the current report, we describe the findings in eleven patients who had an extracranial osteoma and we compare the clinical presentation, the histological features, and the treatment regimens with those reported previously2,6-8,10,11,18,19.
Between 1980 and 1993, eleven patients were diagnosed with and managed for an extracranial osteoma at University Hospitals of Cleveland. Data on age, gender, symptoms, location of the lesion, treatment regimen, and clinical course were compiled for each patient from the medical records. We also reviewed the radiographic and histopathological features of the lesions.
Radiographic Appearance
Histopathological Appearance
Follow-up
Age and Gender
Symptoms
Location of the Lesion
History of Trauma
Preoperative Diagnosis, Treatment, and Outcome For four patients (Cases 2, 8, 9, and 11), a diagnosis of osteosarcoma was considered. Two of these patients (Cases 8 and 9) had a wide en bloc resection; both subsequently had complete relief of pain. The other two patients had an incisional biopsy. In the first patient (Case 2), dense lesions were noted in the humeral head and the glenoid (Fig. 3-A and 3-B). Computerized tomography revealed a dense mass protruding posteriorly into the surrounding soft tissue and the joint space (Fig. 3-C). A bone scan showed increased uptake in the humeral head, and a biopsy of a specimen from the humeral head revealed an osteoma. The symptoms persisted for one-half year after the biopsy. Then, because of constant pain attributed to the osteoma protruding into the joint space, the humeral head was resected and a hemiarthroplasty was performed. Gross examination of the humeral head revealed a bone mass measuring 2.2 by 1.4 by 1.4 centimeters and extending to the articular surface. The histopathological findings were similar to those of the previous biopsy and confirmed the diagnosis of an osteoma (Fig. 1-A). Approximately one year later, the hemiarthroplasty was revised because of loosening, and the symptoms resolved. The second patient (Case 11) who had an incisional biopsy had no additional treatment after that procedure; the injury of the knee healed and the patient became asymptomatic. Two patients (Cases 1 and 5) had a preoperative diagnosis of an osteoid osteoma; both were managed successfully with an excisional biopsy. One of these patients (Case 5) was a twenty-four-year-old man who had had pain in the right thigh for a year. A radiograph showed a medullary sclerotic lesion with no nidus in the mid-part of the femoral canal (Fig. 2-A). Computerized tomography demonstrated a sclerotic lesion attached to the endosteal surface (Fig. 2-B). A bone scan revealed mildly increased uptake in the area of the lesion. An osteoid osteoma was suspected, and an en bloc resection was performed. A radiograph of the specimen also failed to demonstrate a nidus (Fig. 2-C). Histopathological examination revealed a medullary osteoma. Postoperatively, the patient had complete relief of pain. One patient (Case 6) had a preoperative diagnosis of medullary osteosclerosis, and burring of the canal was performed. The symptoms resolved. In the remaining four patients (Cases 3, 4, 7, and 10), all of whom had a spinal lesion, a benign process was assumed but no definite preoperative diagnosis was made. Three of these patients (Cases 3, 4, and 7) had a subtotal or marginal excision. (The excision was considered marginal when there was a border of normal tissue of less than three millimeters.) Two patients (Cases 3 and 4) initially had substantial relief of pain, although both occasionally needed analgesics postoperatively. The latter of these two patients had had low-back pain and sciatica on the left side for eighteen years. A dense lesion that had grown considerably during that period was noted in the left ala of the sacrum (Figs. 4-A and 4-B). Computerized tomography showed mild encroachment of the lesion into the left sacral foramen. Left foraminal stenosis of the fourth and fifth lumbar vertebrae was also diagnosed. A decompression laminectomy with removal of the osteoma and a posterolateral arthrodesis from the fourth lumbar to the first sacral vertebra was performed. Initially, the patient did well, but a non-union subsequently developed at the site of the arthrodesis and she had persistent pain that was treated successfully by a neurosurgeon. The third patient (Case 7) did not have relief of the pain. The fourth patient (Case 10) had three consecutive operations before the pain was relieved. It is noteworthy that, during the follow-up period, none of the osteomas recurred.
Illustrative Case Report Physical examination revealed a well developed woman in moderate distress. The cervical spine had a normal range of motion (a maximum of 60 degrees of extension, lateral rotation, and forward flexion). There was slight tenderness to palpation over the mid-cervical portion of the spine posteriorly, but no mass could be felt. Neurologically, she had weakness (grade 4 of 5) of the left deltoid and the external rotators of the shoulder. A loss of sensation to pinprick was noted over the distribution of the sixth cervical dermatome (over the left deltoid region and in the left arm and forearm). Deep tendon reflexes were symmetrical, without abnormal reflexes. Radiographs revealed an extremely dense lesion involving the bodies and posterior elements of the fourth and fifth cervical vertebrae and, to a lesser extent, the superior facet of the sixth cervical vertebra on the left (Figs. 5-A and 5-B). Computerized tomography showed expansion of the mass posteriorly into the soft tissues surrounding the vertebrae and mild encroachment into the spinal canal (Fig. 5-C). Review of a computerized tomography scan made twelve years earlier revealed that this lesion had already been present. No noticeable changes between the two studies were noted. An angiogram revealed anterior displacement of the vertebral artery, but the artery was completely patent. Magnetic resonance imaging showed that the tumor occupied the facet joint, the pedicles, and the laminae at the fourth, fifth, and sixth cervical levels and had expanded posteriorly into the soft tissues (Fig. 5-D). Operative decompression was performed through a midline posterior approach; this was followed by a posterior spinal arthrodesis from the second to the sixth cervical level with use of a bone graft from the iliac crest. Histopathological examination of the resected lesion revealed a juxtacortical osteoma (Fig. 1-B). Immediately after the operation, the patient did extremely well and was free from pain; however, moderate neck pain developed gradually, about a year later, with no neurological deficit. Radiographs revealed a solid fusion and no sign of recurrence of the tumor. Relief of pain was satisfactory with use of analgesics.
Extracranial osteoma is a rare benign tumor that usually occurs in the skull. Only occasionally have these lesions been reported in extracranial locations. The mean age of the eleven patients in our series was forty years, with a range of fourteen to sixty-eight years. A similarly wide-ranging age distribution has been noted previously8. Some authors have reported on more adolescents and young adults1,7,19, while others have noted a predilection for the tumor to develop in the fourth and fifth decades of life18. Our series included seven female and four male patients, but too few extracranial osteomas have been documented to justify a conclusion about distribution according to gender. A preponderance for the female gender (3:1) was also observed by Huvos, but Campanacci, as well as Resnick and Niwayama, reported a predilection for the male gender. Schajowicz noted that juxtacortical osteomas were more common in male patients while medullary osteomas were more common in female patients. In contrast to previous reports7,8,19, all but one of our patients were symptomatic and had dull, aching pain at the time of the initial presentation. Local pain in four patients was accompanied by radicular symptoms that, in part, were due to local nerve-root pressure. Intracranial osteomas usually cause no symptoms2. In the minority of patients, the lesion, depending on its location, may result in a sensation of pressure, interfere with sinus drainage, encroach on the orbital contents, prohibit normal dental formation, or extend into the cranial cavity. Extracranial osteomas similarly have been reported to produce no symptoms2,7,14; these lesions are usually detected on radiographs as incidental findings or present on clinical examination as a painless, enlarging mass13. Rarely, symptoms from direct pressure on adjacent structures such as a joint space5 or nerves3 have been reported. Our series included osteomas in the tibia, femur, fibula, humerus, and spine. Although extracranial osteomas have a predilection for the tibia3,4,7,19 and have been observed in the femur4,7,16,19, ulna16,18, clavicle13,19, fourth metacarpal20, and pelvis5, no osteoma in the spine has ever been reported, to our knowledge. Radiographically, four of our patients had a juxtacortical osteoma and seven, a medullary osteoma7,19. As evidenced in our series, juxtacortical osteomas are uniform, extremely dense, well circumscribed lesions. The borders are usually lobulated19, and the size usually ranges from one to four centimeters and does not exceed ten centimeters7,10. Little or no reactive new-bone formation is observed at the interface with underlying normal bone6,7,20. Medullary osteomas, while radiographically similar to juxtacortical osteomas, are usually smaller and arise on or immediately adjacent to the endosteum. The histopathological criteria for the diagnosis of a cranial osteoma have been described previously in detail2,4,6,10,11,14,18 and apply equally to lesions in extracranial sites4,7. These lesions typically are characterized by dense, compact lamellar bone; numerous narrow haversian canals of varying size, arranged in a haphazard orientation7; and areas showing mosaic patterns. The lesions in our patients had a histopathological appearance similar to that of osteomas of the skull. The growth potential of osteoma remains unclear. For two of our patients, we were able to compare radiographs made many years previously with preoperative studies made with newer imaging modalities. In one of these patients (Case 3), who had a juxtacortical osteoma of the cervical spine, computerized tomography scans made twelve years apart revealed no major changes. In the other patient (Case 4), who had a medullary osteoma of the sacrum, radiographs demonstrated a much larger lesion than had been seen eighteen years before; the lesion had begun to encroach on the sacral foramen. Histopathological examination of both osteomas did not demonstrate any difference in the degree of cellularity. The differential diagnosis of juxtacortical extracranial osteoma includes osteochondroma and, occasionally, parosteal osteosarcoma. Osteochondroma can usually be excluded on the basis of its irregular shape and its metaphyseal location7. An osteochondroma with an ossified cartilaginous cap might be confused grossly with an osteoma, but the cartilaginous cells of an osteochondroma can usually be appreciated histopathologically. The preoperative distinction between osteoma and parosteal osteosarcoma can be difficult. Patients who have a parosteal osteosarcoma are in the same age-group (the second to the fifth decade of life) as those who have an osteoma, and they also may have an insidious onset of pain, swelling, and a palpable mass. Radiographically, a parosteal osteosarcoma is usually seen as a large, radiodense, oval mass with smooth lobulated or regular margins, attached to the bone's external cortex, which may be thickened. Bone scans may show increased uptake in both a parosteal osteosarcoma and a juxtacortical osteoma. This similar clinicoradiographic picture makes it hard to differentiate an osteoma from a parosteal osteosarcoma, and indeed a preoperative diagnosis of osteosarcoma in two of our patients (Cases 8 and 9) led to a wide excisional biopsy. Occasionally, parosteal osteosarcoma presents with additional radiographic features that are not characteristic of juxtacortical osteoma; a cleavage plane may separate the tumor from the underlying bone, a finding that has not been reported in association with osteoma, to our knowledge. Ossification in parosteal osteosarcoma may be homogeneous and proceeds from the base of the lesion to its periphery. However, parosteal osteosarcomas sometimes contain distinctive radiolucent or cystic areas that are well demonstrated on computerized tomography scans. Parosteal osteosarcomas are almost always located in the metaphysis of the long bones, whereas juxtacortical oteomas are usually found along the diaphysis. The differential diagnosis of medullary extracranial osteoma includes medullary osteosclerosis and a bone island (enostosis). Like medullary osteoma, medullary osteosclerosis is most commonly found in the tibia, is associated with mild-to-moderate pain, and is characterized radiographically by sclerosis in the medullary canal1. In contrast to medullary osteoma, which typically has smooth, defined borders, medullary osteosclerosis has less distinct margins; the dense medullary bone gradually blends with the normal bone. The histopathological features of medullary osteosclerosis, however, are entirely different, especially in that the osseous tissue in the medullary canal is composed mainly of disorganized spicules of reactive woven bone with intervening fibrovascular tissue, in contrast to the dense cortical-like cancellous bone of medullary osteoma. The distinction between an osteoma and a bone island is difficult, as both lesions are similar radiographically and almost identical histopathologically. Both lesions can enlarge over time and can reach a size of more than one centimeter; however, osteomas generally are larger. Bone islands are indeed islands of well defined sclerotic densities17, located in the cancellous part of the bone. Their periphery consists of bone spicules that blend with the surrounding trabecular bone. Histopathologically, they are composed of mature, compact lamellar bone located in the spongiosa, surrounding tiny blood vessels in a concentric, ringlike fashion (osteons). They do not cause symptoms, whereas osteomas produced symptoms in all but one of our patients. Bone islands are of limited clinical importance except when, rarely, they display slow growth or are of considerable size11. In five of our patients who had a medullary osteoma (Cases 1, 4, 7, 10, and 11), the diagnosis of a bone island was considered on the basis of the plain radiographs. With additional imaging modalities, however, this diagnosis was not tenable because of the attachment to the endosteum (all patients), a size substantially larger than that of a typical bone island (all patients), expansion of the cortex (Case 4), and an irregular shape (Cases 1 and 10). In addition, four of these patients (Cases 1, 4, 7, and 10) had pain. The pathogenesis of osteoma remains unknown. Jaffe, in 1958, suggested that it might represent the sclerotic end stage of fibrous dysplasia. In 1975, Aegerter and Kirkpatrick proposed that osteomas are hamartomatous lesions resulting from exaggerated intramembranous bone formation at the bone surface. Schajowicz, however, thought that some osteomas represent an intense reactive sclerosis that hides the central nidus of an osteoblastoma. Finkel et al. noted osteomas in mice after injection with ultrafiltrates of murine spontaneous osteoma extracts; they thought that this suggested a viral etiology. Eight of the eleven cranial osteomas reported by Geschickter and Copeland in 1949 were attributed to a severe blow or a fall. Schajowicz as well as Huvos concurred that the term osteoma has been applied to a wide variety of osseous lesions, some of which clearly have been non-neoplastic and traumatic in origin. Two of three extracranial osteomas reported on by O'Connell et al. were associated with a history of repetitive local trauma. However, those authors did not find histological evidence of previous trauma such as reactive fibrosis or hemosiderin deposition, and they theorized that a reactive process was not capable of producing such a large mass. We did not observe reactive fibrosis or hemosiderin deposition in our patients, and some of the lesions may have represented an end point of the healing process related to previous injury. This lends support to the impression that some extracranial osteomas, like cranial osteomas, may be related to trauma and may represent a response to previous injury to the bone rather than a neoplastic process. We agree with Campanacci that an osteoma should be treated with a total excisional biopsy. In one of our patients (Case 10), partial resection of an osteoma from the body of the fifth lumbar vertebra resulted in no relief of pain and necessitated an additional procedure to remove the remainder of the lesion. Proximal and distal wide margins are not indicated. Marginal excision was performed in most of our patients. None of the osteomas recurred, and ten of the eleven patients had relief of the symptoms. Therefore, we believe that marginal excision is adequate. In conclusion, our experience with these rare lesions indicates that they may be painful, may occur in the spine, and may mimic other osseous processes.
NOTE: The authors thank Dr. Henry H. Bohlman for contributing the cases of osteoma.
*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.
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