Introduction
Background
A bone island, also known as an enostosis, is a focus of compact bone located in cancellous bone.1,2 This is a benign entity that is usually found incidentally on imaging studies; however, the bone island may mimic a more sinister process, such as an osteoblastic metastasis (for example, from prostate cancer).3
Plain-film radiograph of a bone island. Bone islands typically appear as sclerotic, round-to-ovoid intramedullary foci. The long axis of the bone island is aligned parallel to the long axis of the bone.
T1- weighted, sagittal magnetic resonance imaging (MRI) scan of the knee; corresponds to Image 1. Because bone islands are composed of cortical bone, they demonstrate low signal intensity on MRI scans.
Computed tomography (CT) scan. A sclerotic focus that correlates with the radiograph in Image 3 is seen in the right iliac bone adjacent to the sacroiliac joint. CT scan findings of bone islands correlate with their plain film appearance.
Recent reported cases
Ideuchi et al reported a case of a giant bone island of the femur with concurrent ipsilateral femoral head necrosis. Unusual findings included large expansion of the lesion and increased uptake of radionuclide on bone scan. Because the giant bone island was located at the cut surface of the femoral neck, prosthesis insertion was difficult. There was also concern regarding the stability of the cementless prosthesis because of the surrounding bone island. However, after 4 years, there was no evidence of loosening and the patient remained free of symptoms.4
Gould et al provided and in-depth review of 13 cases of bone tumor mimics, that is, a benign osseous lesion that radiologically resembles a bone tumor. The authors note that this is not an uncommon finding. They reported that diagnosis and management of such lesions requires knowledge of the epidemiology, clinical presentations, anatomy, and imaging features of these benign lesions to prevent misdiagnoses.3
Achong reported on a case of increased uptake of radionuclide in a bone island of the lumbar vertebral body. The increased uptake was seen on SPECT imaging but not conventional planar imaging.5
Pathophysiology
Although the exact etiology of bone islands is not clear, they are almost certainly developmental in nature, likely representing cortical bone that has failed to undergo medullary resorption during the process of endochondral ossification. Histologically, bone islands are intramedullary foci of normal compact bone with haversian canals and "thorny" radiations that merge with the trabeculae of surrounding normal cancellous bone.
Frequency
United States
The exact frequency is unknown; however, reports have described a frequency of 1-14%.
Mortality/Morbidity
Bone islands are considered to be benign lesions without associated morbidity or mortality.
Race
No racial predilection is recognized.
Sex
The prevalence of bone islands is approximately equal in men and women.
Age
Bone islands are common in the adult population and are rare in children.
Anatomy
Bone islands are rare in the calvaria, a fact that lends additional support to the theory of a minor endochondral defect as a potential etiology. Bone islands can be found in any osseous site; however, they are most commonly identified in the pelvis, long bones, ribs, and spine.
Presentation
Bone islands are almost invariably asymptomatic lesions that do not result in laboratory abnormalities. A single case report in the English literature describes a patient with a symptomatic, histologically proven bone island of the tibia; the symptoms resolved after curettage.6 Another report described an enlarging mandibular bone island that caused inclination of the adjacent teeth of a young girl.7 A third case report described a symptomatic bone island in the sacrum.8
Preferred Examination
Bone islands, which are usually found incidentally on imaging studies, demonstrate characteristic radiographic findings.
Limitations of Techniques
In the correct clinical context, findings on radiographs are considered diagnostic. However, if the lesion is large or demonstrates increased scintigraphic activity, or if the patient is symptomatic or has a history of malignancy, clinical follow-up and/or biopsy may be warranted.
Differential Diagnoses
| Bone Infarct | Osteosarcoma, Classic |
| Enchondroma and Enchondromatosis | Osteosarcoma, Variants |
| Fibrous Dysplasia | |
| Osteoblastoma | |
| Osteoid Osteoma |
Other Problems to Be Considered
Sclerotic metastasis
Osteoma
Nonossifying fibroma
Osteopoikilosis
More on Bone Island |
 Overview: Bone Island |
| Imaging: Bone Island |
| Follow-up: Bone Island |
| Multimedia: Bone Island |
| References |
| Further Reading |
| Next Page » |
References
Greenspan A. Bone island (enostosis): current concept--a review. Skeletal Radiol. Feb 1995;24(2):111-5. [Medline].
Resnick D. Enostosis, hyperostosis, and periostitis. In: Bone and Joint Imaging. 2nd ed. Philadelphia, Pa: WB Saunders; 1996:1211-4.
Gould CF, Ly JQ, Lattin GE Jr, et al. Bone tumor mimics: avoiding misdiagnosis. Curr Probl Diagn Radiol. May-Jun 2007;36(3):124-41. [Medline].
Ikeuchi M, Komatsu M, Tani T. Giant bone island of femur with femoral head necrosis: a case report. Arch Orthop Trauma Surg. Mar 21 2009;[Medline].
Achong DM. Increased uptake in a vertebral bone island seen only on SPECT. Clin Nucl Med. Aug 2007;32(8):620-3. [Medline].
Park HS, Kim JR, Lee SY, et al. Symptomatic giant (10-cm) bone island of the tibia. Skeletal Radiol. 10 21 2004;[Medline].
Nakano K, Ogawa T, Sobue S, et al. Dense bone island: clinical features and possible complications. Int J Paediatr Dent. Nov 2002;12(6):433-7. [Medline].
Peh WC, Koh WL, Kwek JW, et al. Imaging of painful solitary lesions of the sacrum. Australas Radiol. Dec 2007;51(6):507-15. [Medline].
Greenspan A, Stadalnik RC. Bone island: scintigraphic findings and their clinical application. Can Assoc Radiol J. Oct 1995;46(5):368-79. [Medline].
Brien EW, Mirra JM, Latanza L, et al. Giant bone island of femur. Case report, literature review, and its distinction from low grade osteosarcoma. Skeletal Radiol. Oct 1995;24(7):546-50. [Medline].
Caballes RL, Caballes RA. Polyostotic giant enostoses with strongly positive radionuclide bone scan. Ann Diagn Pathol. Aug 2004;8(4):247-51. [Medline].
Greenspan A, Klein MJ. Giant bone island. Skeletal Radiol. Jan 1996;25(1):67-9. [Medline].
Trombetti A, Noël E. Giant bone islands: a case with 31 years of follow-up. Joint Bone Spine. Jan 2002;69(1):81-4. [Medline].
Greenspan A, Steiner G, Knutzon R. Bone island (enostosis): clinical significance and radiologic and pathologic correlations. Skeletal Radiol. 1991;20(2):85-90. [Medline].
Couto AR, Bruges-Armas J, Peach CA, et al. A novel LEMD3 mutation common to patients with osteopoikilosis with and without melorheostosis. Calcif Tissue Int. Aug 2007;81(2):81-4. [Medline].
Menten B, Buysse K, Zahir F, et al. Osteopoikilosis, short stature and mental retardation as key features of a new microdeletion syndrome on 12q14. J Med Genet. Apr 2007;44(4):264-8. [Medline].
Stark Z, Savarirayan R. Osteopetrosis. Orphanet J Rare Dis. Feb 20 2009;4:5. [Medline].
Sari I, Simsek I, Guvenc I, Sanal HT, Erdem H, Pay S, et al. Osteopoikilosis coexistent with ankylosing spondylitis and familial Mediterranean fever. Rheumatol Int. Jan 2009;29(3):321-3. [Medline].
Keywords
bone island, enostosis, enostoses, giant bone island, osteopoikilosis
