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Bone Island (Enostosis)

DEFINITION AND PATHOGENESIS

  • A benign, rarely symptomatic lesion, usually very small, of unknown etiology

IMPORTANCE

  • Commonly found incidentally, and can be mistaken for lesions which require bx

CLINICAL FEATURES

  • Usually asymptomatic
  • Symptomatic lesions may become asymptomatic
  • Most common in pelvis, ribs, proximal femur
  • M = F
  • Has been reported in Bannayan-Riley Ruvalcaba syndrome
  • A higher incidence of bone islands has been reported in the hands and feet of pts with lepromatous leprosy and borderline types of leprosy but not in tuberculoid leprosy

RADIOLOGIC FEATURES

  • 2mm-2cm sized round to oval blastic lesion blends with the cancellous bone in a "brush-like" manner
  • Bone scan is cold or only warm (33% >15mm reported active on bone scan)
  • CT scan will show the blastic nature of the lesion, accurately give dimensions, and demonstrate lack of periosteal reaction
  • No surrounding bony destruction/cortical disruption, IM extension, or soft tissue mass associated with the lesion is best demonstrated with MRI (hypointense on T1 and T2)

GROSS PATHOLOGY

  • Sharply defined hard lesion within the IM canal

HISTOLOGIC FEATURES

  • Appearance of misplaced cortical bone within the IM canal: thick lamellar bone with Haversian systems
  • No host bone lamellar bone trapping (seen in callus and osteosarcoma)
  • No atypical nuclei or mitoses

DIFFERENTIAL CLINICOPATHOLOGIC DIAGNOSIS

  • Metastatic bone disease (esp. with multiple lesions, eg, blastic breast mets or prostate CA)
  • Osteoid osteoma
  • Osteoblastoma
  • Enchondroma
  • Bone infarct
  • Fibrous dysplasia
  • Osteomyelitis
  • Osteosarcoma

DISEASE COURSE AND TREATMENT

  • Usually require no tx
  • FU x-ray in one month and every 3 months (X4) in questionable lesions
  • Biopsy in larger lesions to R/O osteosarcoma or in lesions that have size ? > 25% within 6mos, or >50% at 1yr

SPECIAL CONSIDERATIONS

  • OSTEOPOIKILOSIS

    • (Multiple Enostosis, Osteopathia Condensans Disseminata)
    • Hereditary: AD
    • Multiple lesions, referred to as "spotted bone disease"
    • May be associated with multiple osteochondromatosis and keloid formation tendency
    • Cutaneous lesions in 25% (white, closely situated fibrocollagenous infiltrations
      • (Dermatofibrosis Lenticularis Disseminata, "Buschke'Ollendorff Syndrome")
    • May be associated with dwarfism, dystocia, spinal stenosis, joint pain ± effusion
  • GIANT BONE ISLAND

    • Bone island of >2cm in size (4cm reported)
    • "Cumulus cloud" appearance
    • Bx indicated to R/O stage IIA osteosarcoma
  • ANIMAL MODEL

FIGURES

REFERENCES

Bassage LH, Ross MW: Enostosis-like lesions in the long bones of 10 horses: scintigraphic and radiographic features. Equine Vet J 1998 Jan;30(1):35-42.

Bhaskar SN, Cutright DE: Multiple enostosis: report of 16 cases. J Oral Surg 26:321-6,1968.
Broderick TW, Resnick D, Goergen TG, Alazreki N: Enostosis of the spine. Spine 3:167-70,1978. Pubmed
Bsoul SA, Alborz S, Terezhalmy GT, Moore WS: Idiopathic osteosclerosis (enostosis, dense bone islands, focal periapical osteopetrosis). Quintessence Int 2004 Jul-Aug;35(7):590-1.

Carpintero P, Garcia-Frasquet A, Tarradas E, Logrono C, Carrascal A, Carreto A: Bone island and leprosy. Skeletal Radiol 27:330-3,1998. Pubmed
Cerase A, Priolo F: Skeletal benign bone-forming lesions. Eur J Radiol 1998 May;27 Suppl 1:S91-7.

Chhabra A, Kaplan PA, Temple HT: A proximal tibial lesion in a 13-year-old girl. Clin Orthop 365:254-8,61-2,1999.
Erkek E, Hizel S, Sanly C, Erkek AB, Tombakoglu M, Bozdogan O, Ulkatan S, Akarsu C: Clinical and histopathological findings in Bannayan-Riley-Ruvalcaba syndrome. J Am Acad Dermatol 2005 Oct;53(4):639-43.

Greenspan A: Bone island (enostosis): clinical significance and radiologic and pathologic correlations. Skeletal Radiol 20: 85-90,1991. Pubmed

Greenspan A: Bone island (enostosis): current concept - a review. Skeletal Radiol 1995 Feb;24(2):111-5. Pubmed

Greenspan A: Sclerosing bone dysplasias--a target-site approach. Skeletal Radiol 1991;20(8):561-83. Pubmed
Greenspan A, Stadalnik RC: Bone island: scintigraphic findings and their clinical application. Can Assoc Radiol J 46:368-79,1995. Pubmed

Jackson RP, Reckling FW: Intracortical and subperiosteal lesion of unknown etiology. Clin Orthop Relat Res 1978 Jan-Feb;(130):260-2.

Leone A, Costantini A, Guglielmi G, Settecasi C, Priolo F: Primary bone tumors and pseudotumors of the lumbosacral spine. Rays 2000 Jan-Mar;25(1):89-103. Pubmed
Mirra JM, Gold RH: Osseous tumors of intramedullary origin. In Mirra JM (ed): Bone Tumors: Clinical, Radiologic, and Pathologic Correlations. Phliadelphia, Lea & Febiger, 1989, pp 389-430.

Murphey MD, Andrews CL, Flemming DJ, Temple HT, Smith WS, Smirniotopoulos JG: From the archives of the AFIP. Primary tumors of the spine: radiologic pathologic correlation. Radiographics 1996 Sep;16(5):1131-58. Pubmed
Vanhoenacker FM, De Beuckeleer LH, Van Hul W, Balemans W, Tan GJ, Will SC, De Schapper AM: Sclerosing bone dysplasias: genetic and radioclinical features. Eur Radiol 10:1423-33,2000. Pubmed

White LM, Kandel R: Osteoid-producing tumors of bone. Semin Musculoskeletal Radiol 2000;4(1):25-43. Pubmed

Wood AK, Porges WL: A suspected case of enostosis in a German shepherd dog. Aust Vet J 1981 Jul;57(7):349-50.

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