Bone & joints

Other osteogenic tumors

Osteoblastoma


Editorial Board Member: Jose G. Mantilla, M.D.
Borislav A. Alexiev, M.D.

Minor changes: 27 September 2021

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PubMed Search: Osteoblastoma[TI] pathology free full text[SB]

Borislav A. Alexiev, M.D.
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Cite this page: Alexiev BA. Osteoblastoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/boneosteoblastoma.html. Accessed October 24th, 2021.
Definition / general
  • Osteoblastoma is a locally aggressive bone forming tumor, morphologically similar to osteoid osteoma but with growth potential and generally > 2 cm in dimension
Essential features
  • Bone forming tumor composed of trabeculae of woven bone rimmed by plump osteoblasts in a vascularized stroma
  • Well defined tumor borders
  • Absence of host bone permeation
  • Radiology demonstration of a > 2 cm lesion
Terminology
  • Acceptable: epithelioid osteoblastoma
  • Not recommended: pseudomalignant osteoblastoma, aggressive osteoblastoma
ICD coding
  • ICD-O: 9200/1 - osteoblastoma, NOS
  • ICD-11: 2E83.Z & XH4316 - benign osteogenic tumors, unspecified & osteoblastoma, NOS
Epidemiology
Sites
Pathophysiology
  • Expresses Runx2 and Osterix, transcription factors involved in osteoblastic differentiation (Hum Pathol 2010;41:1788)
Etiology
  • Unknown
Diagrams / tables

Images hosted on other servers:
Epidemiology and localization

Epidemiology and localization

Clinical features
  • Earliest symptom in most patients is nonspecific pain, characterized as a dull ache that is less severe at night than during the day (Neurosurg Focus 2016;41:E4)
  • Pain is unlikely to be relieved by salicylates (PLoS One 2013;8:e74635)
  • Tumors located in the spine can press on nerves; when this happens, patients usually develop neurological symptoms in the legs, such as numbness, weakness or pain (PLoS One 2013;8:e74635)
  • Can produce beta hCG as a paraneoplastic manifestation (Skeletal Radiol 2017;46:1187)
Diagnosis
  • In many cases, the diagnosis is suggested by the tumor location, size and appearance on Xray, computed tomography and magnetic resonance scans
  • Definitive diagnosis usually requires a biopsy
Radiology description
  • Characteristic appearance on radiographs is a dense shell of bone surrounding the lesion, with some tumors resembling osteoid osteoma with a radiolucent nidus and surrounding sclerotic changes
  • In some cases, the bony shell tends to be very thin, with expansion into adjacent soft issues (Neurosurg Focus 2016;41:E4, Eur Spine J 2015;24:1778)
  • Cortical expansion and destruction are common radiographic findings (Hum Pathol 1994;25:117)
Radiology images

Contributed by Borislav A. Alexiev, M.D. and David R. Lucas, M.D.
Left frontal sinus mass

Left frontal sinus mass

Calcified mass

Calcified mass

T7 osteoblastoma with central nidus

T7 osteoblastoma with central nidus

Prognostic factors
Case reports
Treatment
Gross description
Gross images

Contributed by Borislav A. Alexiev, M.D. and David R. Lucas, M.D.
Bony mass with nidus

Bony mass with nidus

Osteoblastoma of clavicle

Osteoblastoma of clavicle

Spinal T7 osteoblastoma

Spinal T7 osteoblastoma

Microscopic (histologic) description
  • Expansile, surrounded by a sclerotic rim, may or may not have a central sclerotic nidus (Arch Pathol Lab Med 2010;134:1460)
  • Composed of interanastomosing trabeculae of woven bone, set within loose edematous fibrovascular stroma, often with extravasated erythrocytes (StatPearls: Osteoblastoma [Accessed 8 July 2021])
  • Tumors show a spectrum of bony maturational changes ranging from cords and clusters of activated osteoblasts associated with minimal osteoid to lace-like wispy osteoid to broad anastomosing trabeculae of woven bone to sclerotic sheets of woven bone (Arch Pathol Lab Med 2010;134:1460)
  • Osseous trabeculae are lined by a single layer of osteoblasts
  • Diffusely scattered osteoclast type, multinucleated giant cells are often present
  • Degenerative cytologic atypia characterized by cells with large degenerated nuclei and smudged chromatin may be present
  • Secondary aneurysmal bone cysts can occur, most commonly in large or expanded lesions
  • Rarely, one finds cartilage or chondro-osseous matrix within an osteoblastoma
  • Mitotic rate may be high but atypical mitoses are not present
  • Does not infiltrate or permeate pre-existing lamellar bone structures (StatPearls: Osteoblastoma [Accessed 8 July 2021])
  • Epithelioid osteoblastoma is a rare variant characterized histologically by epithelioid osteoblasts and clinically by local recurrences if not completely excised (J Foot Ankle Surg 2020;59:1279)
Microscopic (histologic) images

Contributed by Borislav A. Alexiev, M.D. and David R. Lucas, M.D.
Well marginated lesion

Well marginated lesion

Loose edematous fibrovascular stroma

Loose edematous fibrovascular stroma

Osseous trabeculae

Osseous trabeculae

Demarcated tumor

Demarcated tumor

Activated osteoblasts

Activated osteoblasts


Anastomosing trabeculae

Anastomosing trabeculae

Central nidus of sclerotic woven bone

Central nidus of sclerotic woven bone

Osteoblastoma high power

Woven bone trabeculae with osteoblastic rimming

Degenerative atypia

Degenerative atypia

Cytology description
  • Cellular smears with the presence of mononuclear and binucleated osteoblasts, along with scattered osteoclastic giant cells and uniform spindle cells entangled in myxoid stroma (Diagn Cytopathol 2015;43:218)
  • No necrosis and no atypical mitosis are observed (Cytojournal 2018;15:20)
Cytology images

Contributed by David R. Lucas, M.D.
Cytology smears

Cytology smears

Immunofluorescence description
  • Fluorescence in situ hybridization using split apart probes for FOS shows a segregated red and green signal (Virchows Arch 2020;476:455)
Negative stains
Electron microscopy description
  • Osteoblasts in osteoblastoma resemble normal osteoblasts with few exceptions: irregular, indented nuclei and occasional mitochondria with curved cristae and electron lucent areas (Cancer 1977;39:2127)
    • Ovoid or elongated osteoblasts with eccentric nuclei with irregular, indented nuclear membrane and condensed chromatin towards the periphery and abundant rough endoplasmic reticulum and well developed Golgi apparatus (Acta Pathol Jpn 1979;29:791)
  • Osteocytes and osteoclasts resemble their normal counterparts
    • Osteocytes with less prominent rough endoplasmic reticulum and well developed Golgi apparatus
    • Osteoclasts with sparse rough endoplasmic reticulum and numerous mitochondria
  • Osteoprogenitor cells in different stages of maturation
  • Calcified matrix and osteoid
  • Many blood vessels of varying caliber with osteoblasts in different stages of differentiation in the perivascular spaces
  • Large numbers of red blood cells and few monocytoid cells and histiocytes
Electron microscopy images

Images hosted on other servers:
Osteoblasts with eccentric nuclei

Osteoblasts with eccentric nuclei

Osteoblast with indented nucleus

Osteoblast with
indented nucleus

Molecular / cytogenetics description
  • Homo or hemizygous deletions in chromosome 22
  • Losses of ZNRF3, KREMEN1 and NF2 (inhibitors of the Wnt / beta catenin pathway) (PLoS One 2013;8:e80725)
Sample pathology report
  • Left frontal sinus mass, resection:
    • Osteoblastoma (see comment)
    • Comment: Radiology images demonstrate a calcified lobulated lesion centered in the mid left frontal sinus, 3.2 cm in greatest dimension. Histologically, the neoplasm is composed of interanastomosing trabeculae of woven bone, set within loose edematous fibrovascular stroma, with extravasated erythrocytes. The osseous trabeculae are lined by a single layer of osteoblasts. Diffusely scattered osteoclast type, multinucleated giant cells are present. The neoplasm is surrounded by a sclerotic rim. There is no infiltration of pre-existing lamellar bone structures. Rare mitotic figures and no necrosis are seen. Immunohistochemically, positive staining for FOS and nuclear beta catenin in lesional cells is present. Overall, the appearance on computed tomography and magnetic resonance scans, size (> 2 cm), morphological features and immunohistochemical profile support the diagnosis of osteoblastoma.
    • The prognosis of osteoblastoma is excellent, with most patients cured following the initial surgical treatment. Local recurrence is a relatively common complication, with rates ranging from 15% to 25%.
Differential diagnosis
Additional references
Board review style question #1

A 31 year old man presented with an aggressive appearing thoracic spine lesion measuring 2.8 cm in greatest dimension. Hematoxylin eosin stains demonstrate interanastomosing trabeculae of woven bone, set within loose edematous fibrovascular stroma, with extravasated erythrocytes. There is a spectrum of bony maturational changes ranging from cords and clusters of activated osteoblasts associated with minimal osteoid to lace-like wispy osteoid to broad anastomosing trabeculae of woven bone to sclerotic sheets of woven bone. The osseous trabeculae are lined by a single layer of osteoblasts. Diffusely scattered osteoclast type, multinucleated giant cells are present. The neoplasm is surrounded by a sclerotic rim. There is no infiltration of pre-existing lamellar bone structures. Rare mitotic figures and no necrosis are seen. Immunohistochemical stains for FOS and beta catenin (nuclear) are positive in tumor cells, while all of the following are negative: keratin AE1 / AE3, H3F3A (G34W) and p53. The tumor is negative for USP6 rearrangement.

Which of the following is most likely the correct diagnosis?

  1. Aneurysmal bone cyst
  2. Giant cell tumor of bone
  3. Osteoblastoma
  4. Osteoid osteoma
  5. Osteosarcoma
Board review style answer #1
C. Osteoblastoma

Comment Here

Reference: Osteoblastoma
Board review style question #2
Which of the following is true about osteoblastoma?

  1. Osteoblastoma is more common in females
  2. Predilection for the spine and the sacrum (40 - 55%)
  3. Tumor is positive for H3F3A (G34W)
  4. Tumor permeation of the surrounding host tissue structures is frequently identified
  5. Tumors of the mandible are associated with a poor prognosis
Board review style answer #2
B. Predilection for the spine and the sacrum (40 - 55%)

Comment Here

Reference: Osteoblastoma
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