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Year : 2013  |  Volume : 56  |  Issue : 1  |  Page : 71-72
Bizarre parosteal osteochondromatous proliferation of phalanx

1 Department of Pathology, BPS Government Medical College for Women, Khanpur Kalan, Sonepat, Haryana, India
2 Department of Orthopaedics, BPS Government Medical College for Women, Khanpur Kalan, Sonepat, Haryana, India

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Date of Web Publication6-Aug-2013

How to cite this article:
Rana P, Duhan A, Verma S, Siwach RC. Bizarre parosteal osteochondromatous proliferation of phalanx. Indian J Pathol Microbiol 2013;56:71-2

How to cite this URL:
Rana P, Duhan A, Verma S, Siwach RC. Bizarre parosteal osteochondromatous proliferation of phalanx. Indian J Pathol Microbiol [serial online] 2013 [cited 2022 Jan 22];56:71-2. Available from: https://www.ijpmonline.org/text.asp?2013/56/1/71/116162


Bizarre parosteal osteochondromatous proliferation (BPOP) is an uncommon benign tumor usually presenting as bony swelling on the surface of bone. This lesion occurs as an exophytic outgrowth from the cortical surface, mostly in tubular bones of hands and feet. Nora et al.[1] in 1983 first described them resulting in the eponym Nora's lesion. [1],[2] This can be confused with various benign and malignant conditions, as grossly with osteochondroma and histologically can mimic chondrosarcoma and juxtacortical osteosarcoma due to marked proliferative activity and bizarre, enlarged binucleated chondrocytes. [3] Therefore, radiologic and gross histological appearance must be considered. The treatment modality includes local excision though there is high risk of local recurrence.

The patient being reported was a 45-year-old female who presented with slowly progressive swelling on the proximal phalanx of left thumb. There was no history of pain or trauma preceding swelling. Physical examination revealed firm to hard lesion which was fixed to underlying bone; however, the overlying skin was intact and non-adherent, with mild tenderness on deep palpation. There was mild restriction of movements of inter-phalangeal joint. Neurovascular examination was unremarkable. All laboratory investigations were within normal limits. Roentgenograms showed a bony mass around the distal half of the proximal phalanx of the left thumb, which was well circumscribed on the dorsal aspect, with scalloping effect on the underlying bone, along with mild periosteal reaction. There was no medullary involvement and no breach in the cortex [Figure 1]. Excisional biopsy of the lesion was contemplated. The resected tissue on histopathologic examination revealed disorganized proliferation of fibrous tissue, cartilage, and bone, with the cartilaginous component showing irregular groups of enlarged binucleated and bizarre chondrocytes at places, confirming the diagnosis of BPOP [Figure 2]. The patient on the last follow-up was symptom free and without any local recurrence.
Figure 1: Plain X-ray showing the calcifi ed mass around the proximal phalanx of the left thumb; bett er circumscribed on dorsal aspect

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Figure 2: Disorganized proliferati on of fi brous ti ssue, carti lage, and bone, with the carti laginous component showing irregular groups of enlarged, binucleated, and bizarre chondrocytes at places: (a) H and E, ×200; (b) H and E, ×100; (c) H and E, ×200; (d) H and E, ×200

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In 1983, Nora et al. [1] first described and reported 35 cases of BPOP. [2] This is a rare reactive mineralizing mesenchymal lesion that typically affects the surfaces of bones in hands and feet, usually proximal and middle phalanges and the metacarpal and metatarsal bones. The hands are four times commonly affected than the feet. The lesion has been reported in long bones and skull. [4] The age of onset ranges from 8 to 74 years, mostly affecting between 20 and 35 years with no gender difference. Grossly, this is single or multi-loculated lesion with diameter ranging from 5 to 40 mm and appears blue giving "blue bone" appearance. This arises directly from cortical surface of bone with normal underlying bone. In some cases, they show speculation or irregularity causing diagnostic dilemma. [2]

Although it has distinct clinical, radiologic, and histological appearance, still it may be confused with various benign and malignant lesions. It must be distinguished from parosteal osteosarcoma owing to its parosteal location, but the latter rarely involves hands and feet. Moreover, absence of cellular atypia distinguishes this from osteosarcoma. It might mimic osteochondroma because of its surface, location, and cartilaginous component, but exostosis is relatively uncommon in small bones. The medullary component of the stalk of exostosis is in continuity with medullary cavity of the parent bone and shows no signs of atypia on microscopy. Other benign non-neoplastic lesions like periostitis ossificans, florid periostitis, and turret exostosis may also simulate BPOP. It has been proposed that all these lesions are part of same lesional spectrum. [4]

Horiguchi et al.[5] showed the expression of basic fibroblastic growth factor in chondrocytes; chondromedulin-1 in cartilaginous cap, and vascular endothelial growth factor in chondrocytes near osteocartilaginous interface of lesion. These findings suggest that processes in cartilaginous cap of BPOP are similar to enchondral ossification in growth plate, hence concluding that BPOP is a reparative process after periosteal injury.

The treatment is simple excision, but the recurrence rate can be as high as 50%, which usually occurs within 2 months to 2 years. [3] However, en bloc negative margin excision, complete removal of pseudocapsule, and decortications of underlying cortex prevent recurrence. Even in recurrence, repeat wide excision is advised rather than the aggressive surgery. [1]

With this report, we suggest that we should consider the clinical, radiologic, and histopathologic findings in order to arrive at the correct diagnosis and avoid wrong diagnosis as many conditions may simulate BPOP. Underreporting is not uncommon as it is often misdiagnosed as osteochondroma. High index of suspicion so as not to miss the correct diagnosis is of paramount importance. One should avoid aggressive management as a mutilating surgery for this benign condition, though prone to recurrence.

   Acknowledgment Top

The authors acknowledge the contribution of Prof. Z. S. Kundu for the guidance and correction of the manuscript.

   References Top

1.Nora FE, Dahlin DC, Beabout JW. Bizarre parosteal osteochondromatous proliferations of the hands and feet. Am J Surg Pathol 1983;7:245-50.  Back to cited text no. 1
2.Suresh SS. Nora's lesion of the second toe. Indian J Orthop 2010;44:342-4.  Back to cited text no. 2
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3.Agarwal MG, Prabhudesai SG, Jambhekar NA, Duggal A, Puri A. Bizarre parosteal osteochondromatous proliferation of the phalanx. SICOT online report E020 2003. Available from: http://www.sicot.org/resources/File/IO_reports/01-2003/5-01-2003.pdf [Last accepted on 2003 Jan 21].  Back to cited text no. 3
4.Gruber G, Giessauf C, Leithner A, Zacherl M, Clar H, Bodo K, et al. Bizarre parosteal osteochondromatous proliferation (Nora lesion): A report of 3 cases and a review of the literature. Can J Surg 2008;51:486-9.  Back to cited text no. 4
5.Horiguchi H, Sakane M, Matsui M, Wadano Y. Bizarre parosteal osteochondromatous proliferation (Nora's lesion) of the foot. Pathol Int 2001;51:816-23.  Back to cited text no. 5

Correspondence Address:
Amrita Duhan
H. No. 143, Sector 4, Rohtak - 124 001
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.116162

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