Bizarre Parosteal Osteochondromatous Proliferation

Bizarre parosteal osteochondromatous proliferation
Other names: Nora lesion or Nora disease (not recommended)[1][2]
Bizarre parosteal osteochondromatous proliferation, middle finger
Specialty	Orthopedics
Symptoms	Painless lump in finger or toe[1]
Risk factors	Possibly trauma in a minority[1]
Diagnostic method	Medical imaging[1]
Differential diagnosis	Mainly subungal exostosis[1]
Treatment	Surgical excision.[1]
Prognosis	Up to 50% recur after surgery[1]
Frequency	<5% of cartilage tumors,[3] Males=Females[1]

Bizarre parosteal osteochondromatous proliferation (BPOP) is a type of non-cancerous bone tumor belonging to the group of cartilaginous tumors.^[1][4] It is generally seen in the tubular bones of the hands and feet,^[5] where it presents with a rapidly growing 1-3cm painless lump, usually in a finger or toe.^[1][2]

BPOP is composed of bone, cartilage and spindle cells.^[1] A small number of people have reported previous trauma.^[1]

Diagnosis is by medical imaging.^[1] Treatment is by surgical excision.^[1] Up to 50% recur after surgery.^[1]

It occurs more often in the 20s and 30s,^[1] and combined with subungal exostosis, accounts for less than 5% of cartilage tumors.^[3] Males and females are affected equally.^[1] The condition was first described in 1983 by Frederick E. Nora.^[5][6]

Signs and symptoms[edit | edit source]

BPOP generally presents with a rapidly growing 1-3cm painless lump in a finger or toe.^[1][2]

Mechanism[edit | edit source]

It is composed of bone, cartilage and spindle cells.^[1] A small number of people have reported previous trauma.^[1]

Diagnosis[edit | edit source]

Medical imaging usually shows a well-defined wide-based bony growth on the surface of bone.^[5] It can be pedunculated and irregular, giving it a "bizarre" appearance, and is not connected to underlying bone.^[2]

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  X-ray left foot: Bizarre parosteal osteochondromatous proliferation in 2nd toe

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  MRI mid-upper arm

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  MRI mid-arm axial view

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  X-ray hand, BPOP 2nd metacarpal

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  X-ray hand, BPOP 2nd metacarpal (side view)

Histopathology[edit | edit source]

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  Bone Bizzare Parosteal Osteochondromatous Proliferation

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  Bone Bizzare Parosteal Osteochondromatous Proliferation

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  Bone Bizzare Parosteal Osteochondromatous Proliferation

Differential diagnosis[edit | edit source]

BPOP is distinct from subungal exostosis.^[1][5] Granulomatous infection may also appear similar.^[2] Other differential diagnoses include:

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  Turret exostosis^[5]

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  Periosteal chondroma^[5]

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  Parosteal osteosarcoma^[5]

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  Periosteal chondrosarcoma^[5]

• 

  Osteochondroma^[1]

• 

  Florid reactive periostitis^[5]

• 

  Myositis ossificans^[2]

Treatment[edit | edit source]

Treatment is by surgical excision.^[1]

Outcomes[edit | edit source]

Bizarre parosteal osteochondromatous proliferations are non-cancerous with no risk of spread.^[5] They may invade local tissue and recurrence after surgery can occur in up to 50%.^[1][5]

Epidemiology[edit | edit source]

They are most often seen in people in their 20s and 30s.^[1] Combined with subungal exostosis, account for less than 5% of cartilage tumors.^[3] Males and females are affected equally.^[1][5]

History[edit | edit source]

Bizarre parosteal osteochondromatous proliferation was first described by Frederick E. Nora in 1983.^[5][6] Generally in the US, it has been thought of as a mouthful and hence it is sometimes referred to as Nora's lesion.^[7]

Other animals[edit | edit source]

In 1998 a report of a similar lesion to BPOP was reported in a wallaby.^[8]

References[edit | edit source]