Age / Sex : 34 / F

34/F

C.C.: Left shoulder pain and palpable mass for about 6 months(growing tendency) (Click to enlarge)
 

Bizarre pariosteal osteochondromatous proliferation(BPOP) or Nora's lesion(proxiaml humerus)

Discussion

Findings:
1) Plain radiography - lobulated bony mass at the lateral aspect of proximal metaphysis of the left humerus
2) CT - parosteal ossified mass contiguous with adjacent humeral cortex. - intact cortex of underlying bone. - no continuity with medullary cavity.
3) MRI - parosteal ossified mass covered with cartilage cap. - peripheral and partial Gd-enhancement. - well demarcation from overlying soft tissue. - no involvement of adjacent humeral bone marrow

Differential Diagnosis:
- Bizarre parosteal osteochondromatous proliferation (BPOP) or Nora's lesion
- osteochondroma
- parosteal osteosarcoma
- myositis ossificans
- heterotopic chondro-ossification
- florid reactive periostitis
- subungual exostosis
- turret exostosis
- streess fracture with extensive callous formation

Diagnosis: Bizarre parosteal osteochondromatous proliferation (BPOP) or Nora's lesion

Discussion:
- rare, benign lesion that was first described by Nora et al. in 1983 in the hands or feet of young adults.
- short tubular bone involvement > long bone.
- Minor trauma is an etiologic factor in the development of BPOP.
- Antecedent trauma is reported in the patient's history from 0% to 50% of cases.
- Myositis ossificans and florid reactive periostitis may progress to BPOP.
- high recurrence rate after surgical resection, up to 55% of cases
* Radiographic findings
- dense, non-homogeneous and often multilobulated mass with a broad base attached to the bone cortex.
- heavy mineralization with sclerotic appearance.
- occasionaly, rapid growth and aggressive features on imaging studies.
- no cortical or permeative bone destruction.
- no continuity between mass and medullary cavity of underlying bone.
- positive scintigraphy with an intense tracer uptake in the lesion.
* MRI features
- useful in differentiating BPOP from several of its mimickers.
- low signal on T1WI, high signal on STIR imaging.
- variable signal on FSE T2 and GRE sequences, probably related to the relative amounts of cartilage present within the lesion.

References:
1. Ryu KN, Park YK, Han CS. Radiological Findings of Bizarre Parosteal Osteochondromatous Proliferation. Journal of the Korean Radiological Society 1999;41(3):571-575.
2. Shin BK, Cho HD, Yum BW, et al. Bizarre Parosteal Osteochondromatous Proliferation of the Femur (Nora’'s Lesion). J. of Korean Bone & Joint Tumor Soc 1999;5(3):178-182.
3. Ly JQ, Bui-Mansfieldb LT, Taylor DC. Radiologic demonstration of temporal development of bizarre parosteal osteochondromatous proliferation. Journal of Clinical Imaging 2004;28:216–218.
4. Sundaram M, Wang L, Rothman M, et al: Florid reactive periostitis and bizarre parosteal osteochondromatous proliferation: Pre-biopsy imaging evolution, treatment and outcome. Skeletal Radiol 2001;30:192-198.
5. Torreggiani WC, Munk PL, Al-Ismail K, et al. MR imaging features of bizzarre parosteal osteochondromatous proliferation of bone (Nora’'s lesion). Eur J Radiol 2001;40:224–231.