Proliferative periosteal processes of phalanges: a unitary hypothesis

BPOP in early childhood following resection of osteochondroma: report of a case

The diagnosis of an osteochondroma in the short bones of the extremities is atypical and the presentation in infancy is unusual. A 3-month-old female presented for evaluation of radial deviation of the right index finger present since birth. Radiographs showed a broad-based osseous outgrowth with the usual features of an osteochondroma arising from the base of middle phalanx. Initial corrective surgery at 22 months was followed by recurrence of the lesion. Another resection at 4 years confirmed a final diagnosis of BPOP (bizarre parosteal osteochondromatous proliferation). The subsequent pathologic diagnosis of BPOP appears to support the hypotheses concerning the etiology of BPOP as possibly arising from repeated trauma to the metaphysis.

Bizarre Parosteal Osteochondromatous Proliferation (Nora's Lesion) Affecting Carpal Bones of the Hand in a Middle-Aged Female: A Case Report

A 45-year-old woman complained of left wrist pain and swelling for two years accompanied by limited dorsiflexion. Plain X-rays revealed an abnormal bony mass in the carpal bones, further evaluated using computed tomography and magnetic resonance imaging. Upon confirmation of the benign nature surgical excisional biopsy of the lesion, the histopathology confirmed the diagnosis of Bizarre parosteal osteochondromatous proliferation (BPOP). The patient has remained pain-free and actively involved in her routine for the past two years. BPOP, affecting the carpal bones of the hand, are exceptionally rare occurrence. Attentive preoperative evaluation helps in diagnosis and to initiate measures to avoid recurrence.

Bizarre parosteal osteochondromatous proliferation: an educational review

Bizarre parosteal osteochondromatous proliferation (BPOP) is a surface-based bone lesion belonging to the group of benign chondrogenic tumors. The aim of this review is to familiarize the readers with imaging features and differential diagnosis of BPOP, also addressing pathological presentation and treatment options. The peak of incidence of BPOP is in the third and fourth decades of life, although it can occur at any age. Hands are the most common location of BPOP (55%), followed by feet (15%) and long bones (25%). On imaging, BPOP appears as a well-marginated mass of heterotopic mineralization arising from the periosteal aspect of the bone. Typical features of BPOP are contiguity with the underlying bone and lack of cortico-medullary continuity, although cortical interruption and medullary involvement have been rarely reported. Histologically, BPOP is a benign bone surface lesion characterized by osteocartilaginous proliferation with disorganized admixture of cartilage with bizarre features, bone and spindle cells. Differential diagnosis includes both benign-such as florid reactive periostitis, osteochondroma, subungual exostosis, periosteal chondroma and myositis ossificans-and malignant lesions-such as periosteal chondrosarcoma and surface-based osteosarcoma. Treatment consists of surgical resection. Local recurrences are common and treated with re-excision.Critical relevance statement Bizarre parosteal osteochondromatous proliferation is a benign mineralized mass arising from the periosteal aspect of bone cortex. Multi-modality imaging characteristics, pathology features and differential diagnosis are here highlighted to familiarize the readers with this entity and offer optimal patient care.

Bizarre parosteal osteochondromatous proliferation (Nora's lesion) of the hand: management of a rare clinical entity

Bizarre parosteal osteochondromatous proliferation, or Nora's lesion, is a rare benign tumour of the bone, most commonly described in the hands and feet. We present the case of a female patient in her 20s attending the hand clinic with a sudden onset, atraumatic swelling on the proximal phalanx of her right ring finger. The patient retains good hand function and remains asymptomatic 3 months after surgical excision. Our case highlights the importance of being aware of this diagnosis and differentiating it from other malignant, as well as benign tumours of the hand.

Unusual Site of a Bizarre Parosteal Osteochondromatous Proliferation (Nora's Lesion) Involving the Scapula: First Case Report and Review of the Literature

Bizarre parosteal osteochondromatous proliferation (BPOP), also known as Nora's lesion, is a rare benign surface lesion of bone that typically occurs in the hands and feet. We report herein the first case of BPOP occurring in an unusual location, specifically the scapula of a 29-year-old male patient. The lesion exhibited features mimicking those of a peripheral chondrosarcoma because of its atypical location in the axial skeleton and the presence of calcification, which indicates the presence of cartilaginous matrix. Treatment involved a wide surgical resection, and histopathological examination confirmed the diagnosis of BPOP of the bone. At a five-year follow-up, there was no evidence of local recurrence.

Identification of COL1A1/2 Mutations and Fusions With Noncoding RNA Genes in Bizarre Parosteal Osteochondromatous Proliferation (Nora Lesion)

Bizarre parosteal osteochondromatous proliferation (BPOP) (Nora lesion) is a benign bone surface lesion, which most commonly occurs in the digits of young patients and has a high rate of recurrence. Histologically, it is composed of a mixture of disorganized bone, cartilage, and spindle cells in variable proportions and characterized by amorphous "blue bone" mineralization. Recurrent chromosomal abnormalities, including t(1;17)(q32-42;q21-23) and inv(7)(q21.1-22q31.3-32), have been reported in BPOP. However, the exact genes involved in the rearrangements remain unknown. In this study, we analyzed 8 BPOP cases affecting the fingers, toe, ulna, radius, and fibula of 5 female and 3 male patients, aged 5 to 68 years. RNA sequencing of 5 cases identified genetic fusions between COL1A2 and LINC-PINT in 3 cases and COL1A1::MIR29B2CHG fusion in 1, both validated using fluorescence in situ hybridization and reverse transcription (RT)-PCR. The remaining fusion-negative case harbored 3 COL1A1 mutations as revealed by whole-exome sequencing and confirmed using Sanger sequencing. All these genetic alterations were predicted to cause frameshift and/or truncation of COL1A1/2. The chromosomal locations of COL1A2 (7q21.3), LINC-PINT (7q32.3), COL1A1 (17q21.33), and MIR29B2CHG (1q32.2) were consistent with the breakpoints identified in the previous cytogenetic studies. Subsequent screening of 3 BPOPs using fluorescence in situ hybridization identified 1 additional case each with COL1A1 or COL1A2 rearrangement. Our findings are consistent with reported chromosomal abnormalities and implicate the disruption of type I collagen, and perhaps of either noncoding RNA gene as a tumor suppressor, in the tumorigenesis of BPOP. The prevalence and tumorigenic mechanisms of these COL1A1/2 alterations in BPOP require further investigation.

Bizarre Parosteal Osteochondromatous Proliferation (Nora Lesion): A Narrative Review

Background

Bizarre parosteal osteochondromatous proliferation (BPOP), or Nora lesion, is a rare proliferative disease arising from the parosteal region of bones. Although BPOP's pathogenesis is still not certain, modern literature suggests it to be a tumor-like lesion or even a benign neoplasm. Due to the extremely low incidence, to this date studies on the topic are limited to case reports and a few case series. This narrative review aims to resume literature on BPOP and provide an overview of its natural history, morphologic characteristics and prognostic horizon.

Materials and methods

A systematic research of the literature was done to identify studies reporting on patients who suffered from BPOP between 1983 and 2021. We collected data regarding aetiologic and pathogenetic theories, patients' personal data and anamnesis, lesions' location, clinical presentation, imaging features, pathological appearance, treatment and prognosis.

Results

We identified 322 cases of BPOP with a mean age of 34.3 years at the moment of diagnosis. There was no gender difference. The most involved site was the hand, followed by the foot. A history of trauma was reported for 14.7% of the cases. 38.7% of the patients had pain. Literature defined typical radiographic and microscopic patterns that characterize Nora lesions. While imaging is fundamental to orientate towards BPOP, histological evaluation is mandatory to get the definitive diagnosis. To this date, only reliable therapeutic option is represented by surgical resection. BPOP is burdened by a risk of recurrence that accounts to 37.4%.

Conclusion

BPOP is a rare benign disease that should be considered during the differential diagnosis of parosteal lesions, especially in the acral regions. Careful diagnostic evaluations are necessary to get the correct diagnosis and wide margins of resection are recommended to minimize the relatively high risk of local recurrence.

Nora's lesion of the distal ulna: a case report

Nora’s lesion, also known as bizarre parosteal osteochondromatous proliferation (BPOP), is a very rare benign lesion with few published cases. BPOP is more common in adults during the second to third decades of life, and usually occurs on the hands and feet. Radiologically, it appears as a calcified mass attached to the bone cortex that grows rapidly and that recurs easily following resection. Aggressive features on imaging and confusing histopathological findings usually result in misdiagnosis or mistreatment. Herein, we present a case of a rare bony tumour involving the distal ulna presenting as a painless growing mass. An excisional biopsy with clear margins was performed without disturbing the ulnar nerve and arteries. There was no recurrent mass or calcified lesion 1 year after surgery. Based on its rarity and difficult diagnosis, BPOP should be considered in the differential diagnosis of a painless mass in the distal ulnar region. Careful follow-up after surgery is essential, even without lesion recurrence.

Bizarre Parosteal Osteochondromatous Proliferation (Nora Lesion) in Pediatric Phalanges

Bizarre parosteal osteochondromatous proliferation, or Nora tumor, is an uncommon lesion affecting the tubular bones of the hands and feet. Normally arising from the cortical surface and periosteum of these bones, these lesions histologically consist of a hypercellular cartilaginous cap covering a bony stalk that is surrounded by ossified areas and spindle cell stroma. The differential diagnosis includes conditions involving the periosteum such as chondrosarcoma, parosteal osteosarcoma, osteochondroma, turret exostosis, and florid reactive periostitis. The only effective treatment is wide surgical excision; nevertheless, local recurrence rates are extremely high and may necessitate revision surgery. In the present study, we report 3 cases of Nora lesion located in the hand in pediatric patients. The diagnosis in these cases was challenging owing to their presenting symptoms and radiographic findings. The diagnosis was made based on characteristic findings noted on the radiographic images and was confirmed by histological examination following excision.

Bizarre parosteal osteochondromatous proliferation: Rare case affecting distal ulna and review of literature

Bizarre parosteal osteochondromatous proliferation (BPOP) or Nora's lesion, is a rare benign surface-based bone lesion most commonly involving the tubular bones of hands and feet. We report an unusual case of BPOP affecting the distal ulna in a 22-year-old man who presented with a painless wrist mass following injury and was successfully treated with surgical resection. We focus on multi-modality imaging, histopathology, and differential diagnosis (including osteochondroma, florid reactive periostitis, myositis ossificans, and surface-type osteosarcoma), as well as a review of the literature regarding recent concepts on etiology and evolution, spectrum of imaging characteristics and diagnostic overlap, histopathology, as well as treatment options.

Bizarre parosteal osteochondromatous proliferation co-occurring with a metatarsal fatigue fracture: a case report

Background

Bizarre parosteal osteochondromatous proliferation (BPOP) is a relatively rare benign extraperiosteal osteochondroma-like proliferative lesion that shares similarities with malignant tumours in terms of morphology. The aetiology of BPOP has yet to be determined and there are no previous reports of BPOP associated with fracture.

Case presentation

A 57-year-old woman presented with a one-month history of pain and swelling in her right foot, which were worsened by activity and improved with rest. Physical examination revealed a hard, non-mobile mass measuring 1.5 cm × 1.5 cm on the dorsal aspect of the third metatarsal of the right foot. There was overlying erythema and tenderness on palpation. Computed tomography (CT) of the right foot demonstrated a fracture of the neck of the third metatarsal, osteolysis at the fracture site and soft tissue swelling. Bone scintigraphy revealed increased tracer uptake suggesting abnormal bone metabolism at the neck of the third metatarsal. Surgical excision of the lesion was performed. Histopathology and immunohistochemistry confirmed the diagnosis of BPOP.

Conclusion

BPOP is a rare benign lesion that is commonly misdiagnosed. Differential diagnosis is mainly achieved through imaging and histopathological assessment.

Bizarre parosteal osteochondromatous proliferation of the femur: A case report

A 54-year-old man initially presented with left distal thigh pain during walking. Imaging analysis revealed a diffuse calcified or ossified mass adjacent to the medial cortex of the distal femur and absence of continuity with the medulla. We performed resection biopsy. Histological examination revealed a large amount of hypercellular cartilage showing transformation to trabecular bone and BPOP was diagnosed. Postoperative course was uneventful and he remained free of recurrence. The method of resection should depend on the stage of reactive proliferation and whether the lesion is pathologically immature or mature. We also provide a brief review of the literature.

Nora's lesion of 2nd metacarpal treated by wide excision, autologous fibular grafting and metacarpophalangeal joint replacement: A rare case report

Bizarre paroxysmal osteochondromatous proliferation (BPOP) is a rare benign neoplastic lesion predominantly affecting small bones of the hand and known for its recurrence after local excision. We describe a rare case of BPOP involving second metacarpal of the dominant hand which was treated using a novel technique. Wide excision and reconstruction with non-vascularised fibular autograft was performed along with metacarpophalangeal joint replacement. At a follow up of two years, there was no evidence of recurrence and patient had good functional outcome. Hence this modality of treatment could be considered in dealing such cases of BPOP involving the small bones of hand.

Bizarre parosteal osteochondromatous proliferation: 16 Cases with a focus on histologic variability

Bizarre parosteal osteochondromatous proliferation (BPOP) is a benign bone and cartilage forming tumor occurring on the surface of bones, predominantly on the hands and feet. A defining feature of BPOP is the purplish-blue mineralization of cartilaginous tissue, known as 'blue bone.' Here, we report on an institutional series of 16 cases of BPOP, including radiographic, histologic, and histomorphometric features. All tumors were composed of some element of bone, cartilage, fibrous tissue and 'blue bone,' though the amount of each tissue sub-type varied widely. Some cases showed focal 'blue bone' only, however this was a defining feature in all cases.

Peering beneath the surface: Juxtacortical tumors of bone (part I)

Juxtacortical or surface tumors of bone are neoplasms arising from or just outside the cortex, and are composed of different histologic types. Although the imaging appearances of these lesions have similarities to their intramedullary counterparts, their location alters their radiographic and MR characteristics, creating difficulties in diagnosis. Meanwhile, several non-neoplastic lesions, such as stress reaction/stress fracture and indolent infectious processes, compound the differential diagnosis. Neoplastic juxtacortical lesions of bone have been classified into five categories: cartilaginous, fibrous, lipomatous, osseous, and metastatic tumors. Our goal in part one of this review is to illustrate the characteristic radiographic, CT and MR imaging features of various juxtacortical neoplasms, including pathognomonic imaging findings that can aid in diagnosis, and to develop an appropriate differential diagnosis for surface lesions based on imaging characteristics, lesion location and patient age.

Florid reactive periostitis of the long bone: A case series of seven patients

BACKGROUND

Florid reactive periostitis (FRP) is a rare benign periosteal lesion, which mostly involves the tubular bones of the extremities. FRP of the long bone is especially rare. We here report a case series of long bone FRP and also discuss the differential diagnosis and clinical outcome of our series.

PATIENTS AND METHODS

In total, four female and three male patients with long bone FRP and a mean age of 25.1 years were evaluated for this study, from which four upper extremity and three lower extremity FRP lesions were identified. Patients were classified according to the clinical, radiological and pathological manifestations of the lesion.

RESULTS

Periosteal reaction and edema around the lesions were observed in all cases. Calcified mass, bone marrow edema and cortical erosion were observed in six out of seven patients. Moreover, two lesions with peripheral mineralization and zoning appearances were observed. Limb rest and anti-inflammatory therapy proved to be sufficient treatment in all cases. The lesions were spontaneously resolved in all cases, leaving a residual exostosis.

CONCLUSION

Our report indicates that short bone and long bone FRP could reveal different characteristics in some aspects, including the choice of the therapeutic approach. In spite of the favorable clinical outcome of long bone FRP, its differentiation from more aggressive lesions, especially osteosarcoma and osteomyelitis, should still be taken into consideration. In addition, according to our evidence, the implication of the zonal pattern in differential diagnosis of FRP and myositis ossificans (MO) could be re-evaluated.

[Bizarre parosteal osteochondromatous proliferation of the metatarsal bone]

A bizarre parosteal osteochondromatous proliferation (BPOP), also known as a Nora lesion, is a rare benign bone formation. It emanates mainly from the intact cortex of the metaphysis of short tubular bones (hands or feet). Conventional radiographs should be complemented using cross-sectional imaging modalities (CT/MRI). In the absence of symptoms a non-operative regime with radiological and clinical controls is possible. If symptomatic, excision biopsy is the treatment of choice, though a high recurrence rate has been reported. Histopathological examination confirms the diagnosis and typically shows an endochondral ossification zone and an unusually mineralized cartilaginous matrix referred to as "blue bone".

[Benign bone tumors and tumor-like lesions. What must clinicians know about imaging?]

PURPOSE

Benign bone tumors are relatively seldom compared to degenerative and inflammatory skeletal diseases. There are usually diagnostic difficulties because of their markedly high differential diagnostic potential. This leads to problems regarding the further procedure.

PROBLEM

Evaluation of the significance of radiology in the management of benign skeletal lesions.

MATERIAL AND METHODS

Significant diagnostic elements of benign bone tumors are presented by means of data from the well-known literature and personal experiences.

RESULTS

The tasks in radiology when diagnosing primary bone tumors or tumor-like lesions are firstly, detection or exclusion of a lesion, secondly, limiting the differential diagnostic possibilities or reaching a certain diagnosis and thirdly, staging of bone tumors in cases where the disease needs further diagnostic measures. In particular circumstances the diagnostics of disease recurrence can additionally be necessary.

CONCLUSION

The diagnostics of primary and secondary benign (and malignant) bone tumors requires a specialized osteoradiological expertise because of their rarity and the differential diagnostic and differential therapeutic potential. Radiology and pathology are the basis of diagnosing bone tumors and tumor-like lesions. Benign bone tumors and tumor-like lesions can often be diagnosed radiologically; therefore, the choice between a conservative (surveillance) or interventional (surgery) procedure will be correct in most cases.

A bizarre parosteal osteochondromatous proliferation (Nora's lesion) of metatarsus, a histopathological and etiological puzzlement

Nora's lesion (bizarre parosteal osteochondromatous proliferation) is a rare, benign lesion that is composed of differing amounts of cartilage, bone, and spindle cells and an unusual form of calcified cartilage so-called "blue bone". Whether it represents a reactive proliferation or a neoplastic lesion still remains controversial. We present a 24-year-old woman having a 4.5cm two lobulated mass attached to second metatarsus of her left foot. The lesion was hyperintense on magnetic resonance imaging and accompanied by an extensive soft tissue and bone marrow edema. In resection specimen, smaller lobule appeared stuck-on the cortex while the larger one had a broader base and a 0.4cm cartilaginous cap-like formation. The histological picture was best fit to Nora's lesion however showed less fibroblastic tissue and cartilaginous pleomorphism. The lesion also showed areas with cortical invasion and a small focus of fracture callus accompanied by adjacent medullary edema and fat necrosis. The case is presented with the comparative radiologic, macroscopic and microscopic findings for its diagnostic difficulties and etiopathogenetic considerations in favour of a maturation phenomenon in parosteal ostecartilaginous lesions irrespective of the cause.

Non-traumatic calcifications/ossifications of the bone surface and soft tissues of the wrist, hand and fingers: a diagnostic approach

In the absence of obvious trauma, the calcifications/ossifications of the bone surface and soft tissues of the wrist, hand and fingers can be challenging and may not be noticed or lead to unnecessary examinations and monitoring. Although these are usually benign conditions and despite a favorable spontaneous outcome, surgical resection may be required and recurrence may occur. In practice, only paraneoplastic syndromes such as secondary hypertrophic osteoarthropathy (Pierre Marie-Bamberger syndrome) may reveal a malignant tumor, most often pulmonary. We suggest a diagnostic approach based on the initial clinical presentation (acute pain, chronic pain, growth±pain) and the radiological features.

Bizarre parosteal osteochondromatous proliferation (Nora's lesion) of phalanx in a child

Bizarre parosteal osteochondromatous proliferation (BPOP; also called Nora's lesion) is a benign surface osteocartilaginous lesion, which is infrequently reported in world literature. The condition is classically described in the short tubular bones of hands and feet in the second and third decades of life. We present a case report of BPOP of the middle phalanx of middle finger in a 4-year-old girl. The child underwent a wide excision and remained asymptomatic at 2.5 years of follow-up. Our case report highlights the importance of suspecting Nora's lesion in a child. It also helps in delineating a differential diagnosis and discusses the management principles of this rare osteocartilaginous lesion.

"Nora lesion" - Bizarre parosteal osteochondromatous proliferation

Nora lesion is a rare benign parosteal osteochondromatous proliferation involving feet and hand. Aggressive features on imaging and confusing results on histopathological studies make its diagnosis difficult. Since the time of its discovery, only few cases have been reported in the literature. Authors report a case of Nora's lesion on the planto-medial aspect of metatarsal head of great toe of left foot. The diagnosis was suspected by imaging characteristic features and was confirmed by histopathology. Treatment was surgical, with complete excision. There are no clinical or radiological signs of recurrence on further review 1 year post-operatively.

Nora's lesion: bizarre parosteal osteochondromatous proliferation of the tibia

Bizarre parosteal osteochondromatous proliferation is a rare benign condition of locally aggressive and often recurrent osteochondromatous exostosis arising from the bony cortex. We present a case of a patient who presented with this lesion in her tibia, focusing on imaging findings. Because of the lack of information on the disease's natural history, etiology, and clinical course, a multidisciplinary approach is needed for diagnosis and treatment.

Pseudotumors and Reactive Lesions

This article discusses reactive or degenerative processes in bone or periosteal soft tissue that occasionally masquerade as neoplasms. Presentation of the clinical, radiologic, and pathologic features of these processes is provided with an emphasis on the avoidance of overdiagnosis. Clinical, radiologic, and pathologic features of pseudotumors are presented in detail. This article approaches these tumor-like lesions in 2 categories: (1) those in the soft tissue next to bone and (2) those inside bones from the aspect of mineralization and calcification.

Bizarre parosteal osteochondromatous proliferation: a locally aggressive benign tumor

BACKGROUND

Bizarre parosteal osteochondromatous proliferation (BPOP) is a benign lesion of bone, and numerous questions remain unresolved regarding its etiology, diagnosis, and treatment.

QUESTIONS/PURPOSES

We present the Scottish Bone Tumour Registry experience of this rare lesion.

PATIENTS AND METHODS

We performed a retrospective analysis of the Scottish Bone Tumour Registry records. Histologic specimens were reexamined by a musculoskeletal pathologist. Radiographs were reevaluated by a musculoskeletal radiologist.

RESULTS

From 1983 to 2009, 13 cases (13 patients; six male, seven female) were identified. Their ages ranged from 13 to 65 years. All patients presented with localized swelling. Pain was present in five. Antecedent trauma was present in two. Nine lesions affected the hand, three the foot, and one the tibial tuberosity. Twelve lesions were excised and one was curetted. There were seven recurrences of which six were excised. One lesion recurred a second time and was excised. There were no metastases. Radiographs showed densely mineralized lesions contiguous with an uninvolved cortex. Cortical breakthrough was present in one case and scalloping in another. Histologic analysis characteristically showed hypercellular cartilage with pleomorphism and calcification/ossification without atypia, bone undergoing maturation, and a spindle cell stroma.

CONCLUSIONS

BPOP is a rare benign lesion that probably is neoplastic, with no gender predilection, and affecting patients over a wide age range. Previously trauma was considered an etiologic factor, but this no longer seems to be the case. The rate of recurrence was 50%, which may indicate a more extensive resection is required for this locally aggressive lesion. No metastases were reported. BPOP should not be mistaken for, or treated as, a malignant tumor.

LEVEL OF EVIDENCE

Level IV, retrospective case series. See Guidelines for Authors for a complete description of levels of evidence.

Unusual presentation of bizarre parosteal osteochondromatous lesion of the second toe (Nora's lesion)

Bizarre parosteal osteochondromatous proliferation (BPOP) of bone is a rare benign neoplasm. This report presents the first case of BPOP associated with gangrenous changes and ulceration after remaining symptomless for 20 years. The authors hypothesize that the cause of gangrene may be attributed either to vascular occlusion due to pressure, trauma, or malignant transformation of the lesion. Although local excision of the tumor is the treatment of choice, the authors resorted to ray excision, as gangrenous changes and ulceration were present and there was the possibility of malignant change.

[Nora's lesion. Discussion of a rare bone proliferation]

Nora's lesion, also known as "bizarre parosteal osteochondromatous proliferation" (BPOP), was first described in 1983 by the pathologist Nora. This lesion is defined as a proliferation of the bone. In most cases the lesion emanates from the intact cortical substance of short bones. It used to be assigned to reactive, heterotopic ossifications. More recent publications described constant genetic alterations supposing a tumorous genesis. Nora lesions are mostly found in the third or fourth decade of life; a preference of sexes is not described in the literature. They are characterized by a typical appearance in radiological diagnostics, but the diagnosis is ultimately determined by histopathological examination. Surgical resection is the therapy of choice.We report the case of a 29-year-old patient with an undetermined proliferation of the proximal ulna. The diagnosis of a Nora's lesion was made. The therapeutic approach, differential diagnosis and corresponding literature are presented and discussed.

Bizarre parosteal osteochondromatous proliferation of the metatarsal: a pediatric case report and archival review

Bizarre parosteal osteochondromatous proliferations (BPOP), also known as Nora's lesions, are rare tumors occurring most commonly in the hands and feet. They are benign and rarely exhibit radiological evidence of cortical invasion. We report a case of BPOP showing atypical magnetic resonance imaging features that are inconsistent with BPOP and having a novel chromosomal aberration. We also review the BPOP cases in our regional benign bone tumor database.

LEVEL OF CLINICAL EVIDENCE

4.

Pseudosarcomas of soft tissue

One of the most common and important pitfalls in soft tissue pathology are the so-called pseudosarcomas. These lesions are nonneoplastic; however, their rapid growth, hypercellularity, cytologic atypia, and mitotic activity makes them prone to be misinterpreted as sarcoma. The most common of these lesions are fibroblastic/myofibroblastic and matrix-forming proliferations, including nodular fasciitis, proliferative fasciitis and myositis, ischemic fasciitis, massive localized edema, myositis ossificans, and bizarre parosteal osteochondromatous proliferation and related entities. Most of these lesions rarely recur following simple excision; therefore, their accurate recognition helps prevent excessive therapy.

Nora's lesion. Clinical and therapeutic considerations

In this article we report a case of bizarre paraosteal osteochondromatous proliferation (BPOP), also known as Nora's lesion, arising on the distal phalanx of the fifth finger of the hand in a young-adult subject. In this paper, we discuss the possible therapeutic programme related to the grade of severity of the clinical features and underline the rarity of this lesion and the difficulty of diagnosis, which is exclusively histological.

Florid reactive periostitis ossificans of the distal ulna

Florid reactive periostitis is the term used to describe a benign disease characterized by aggressive periosteal reaction and benign soft-tissue inflammation. Although it is considered rare, there are numerous reports in the literature that refer to this disease with different names such as parosteal fasciitis, fasciitis ossificans, benign fibro-osseous pseudotumor, pseudomalignant osseous tumor of soft tissue, and bizarre parosteal osteochondromatous proliferation. As a result, the nomenclature is confusing, and some authors have placed florid reactive periostitis ossificans into the heterogeneous group of pseudomalignant osseous tumors of soft tissue or proliferative periosteal processes, whereas other authors place this entity in the myositis ossificans group. In the same manner, florid reactive periostitis has been considered to be a previous stage of bizarre parosteal osteochondromatous proliferations. This article presents a case of florid reactive periostitis ossificans of the distal ulna in a 13-year-old boy. The patient presented with a painful lesion in the distal ulna, and plain radiographs suggested the presence of a quickly growing periosteal lesion with associated calcification and soft tissue mass. Histologically, the appearance was that of reactive periostitis. The clinical, radiological, and histologic features of florid reactive periostitis are described.

Cortico-medullary continuity in bizarre parosteal osteochondromatous proliferation mimicking osteochondroma on imaging

Bizarre parosteal osteochondromatous proliferation (BPOP), or Nora's lesion, is an unusual surface-based lesion of bone found most commonly in the hands and feet. In the original description of the lesion and in all publications that followed, one of the key imaging characteristics used to define this entity was the lack of cortico-medullary continuity with the underlying bone. The authors present 4 unique cases of pathologically proven BPOP in which cortico-medullary continuity with the underlying bone was demonstrated on imaging. It is believed that florid reactive periostitis, BPOP and turret osteochondroma may reflect points along the same continuum with trauma the likely inciting event. The authors suggest that, given this continuum, it may be possible to have BPOP lesions demonstrating overlapping imaging features with osteochondroma. If this is the case, strict adherence to the standard imaging criterion of lack of continuity between the lesion and the underlying bone may lead to misdiagnosis of these unusual cases of BPOP as osteochondromas.

Bizarre parosteal osteochondromatous proliferation of the proximal humerus: case report

Bizarre parosteal osteochondromatous proliferation (BPOP), or Nora's lesion, is a rare lesion of bone occurring predominantly in the long bones of the hands and feet. It exists as a puzzling clinical entity of uncertain origins and high recurrence rates after surgical resection. To our knowledge, this clinical entity has not been reported in the proximal aspect of the humerus. An interesting report of a lesion occurring in the proximal humerus, which initially was misinterpreted as a parosteal osteosarcoma, is discussed outlining the clinical, radiographic and pathologic features of the BPOP lesion.

Nora's lesion, a distinct radiological entity?

OBJECTIVE

To describe the radiological findings of "Bizarre parosteal osteochondromatous proliferation"(BPOP)-otherwise known as Nora's lesion, to describe the natural evolution of BPOP and to assess radiologically if BPOP is indeed part of a spectrum of reactive lesions including florid reactive periostitis and turret exostosis.

DESIGN

Four experienced musculoskeletal radiologists studied plain radiographs and other imaging documents of histologically-proven Nora's lesions, looking for soft-tissue changes, periosteal reaction/calcification and calcified/ossified pseudotumours, and compared those findings with findings on pathology reviewed by a peer group of pathologists.

PATIENTS

Twenty-four Nora's lesions originating from a series of 200 consecutive, histologically-verified bone (pseudo)tumours of the hand, seen by the "Netherlands Committee on Bone Tumours" for review and second opinion.

RESULTS

Nora's lesions have a recognised presentation on radiographs without specific MR characteristics. Natural evolution could be assessed retrospectively in four cases. Recurrent lesions were seen in seven cases and are difficult to differentiate from primary lesions.

CONCLUSIONS

Nora's lesion, defined as a "well-marginated mass of heterotopic mineralization arising from the periosteal aspect of an intact cortex, without medullary changes" has a distinct radiological presentation and is part of a spectrum of reactive lesions which includes florid reactive periostitis and turret exostosis. As it has a distinct radiological appearance, differential diagnosis of malignant lesions such as osteosarcoma and chondrosarcoma should be clear. It does not require immediate biopsy unless the natural evolution is unspecific.

Heterotopic ossification: a review

Heterotopic ossification is the formation of bone in the soft tissues. Soft tissue bone deposition may range from the minimal and inconsequential to massive and clinically significant. In some clinical settings it is a predictable finding with an unpredictable course and in other settings it may be diagnostically confounding. Heterotopic ossification may be encountered in clinically disparate disease processes and circumstances. We review the genetic, neurogenic, post-traumatic, post-surgical and "reactive" causes of heterotopic ossification and discuss some current concepts of its pathogenesis.

Prolifération ostéocartilagineuse parostéale bizarre ou tumeur de Nora. À propos de deux cas

Bizarre parosteal osteochondromatous proliferation, or Nora's tumor, is an uncommon lesion, involving mostly tubular bones of hands and feet, arising from the cortical surface. It must be distinguishable from chondrosarcoma, parosteal osteosarcoma and florid reactive periostitis. It is a benign lesion, characterized by a proliferation of chondroid, bony and fibrous tissues. The authors report two cases involving the hand. The diagnosis can be made thanks to imaging techniques and confirmed by histological examination. The treatment is surgical, namely complete excision but there is a high rate of local relapse.

Bizarre parosteal osteochondromatous proliferation with a t(1;17) translocation

Bizarre parosteal osteochondromatous proliferation (BPOP) is a benign lesion that tends to recur repeatedly. Histologically, BPOP contains three components (cartilage, bone, and spindle cells) in differing amounts. The histological findings of BPOP are similar to those of florid reactive periostitis (FRP) and subungual (Dupuytren's) exostosis. Some authors have postulated that all of these conditions are reactive proliferative lesions representing different phases of reactive processes. Whether BPOP is a reactive proliferative lesion or a neoplastic lesion, however, remains controversial. Recently, a t(1;17)(q32;q21) translocation in BPOP was detected using chromosome banding and fluorescence in situ hybridization (FISH) analyses. Here, we describe a 39-year-old Japanese female with BPOP arising in the proximal phalanx of her third toe. A cytogenetic analysis revealed a t(1;17)(q 42;q23) translocation. The breakpoints in this case are located close to those of previously reported cases. These results suggest that t(1;17) is a distinct translocation of BPOP and that BPOP is a neoplastic lesion, rather than a reactive proliferative process.

Surface lesions of the bones of the hand

Surface lesions involving the bones of the hand are uncommon. This pictorial review illustrates the spectrum of conditions including benign primary bone tumours, malignant primary bone tumours and non-neoplastic disorders. The review focuses on the radiographic appearances of these lesions and other techniques such as CT and MR imaging that may suggest a specific diagnosis.