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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.

Background Bizarre parosteal osteochondromatous proliferation (BPOP) is a rare benign bone tumor, it is also called “Nora’s lesion”. The lesion is characterized by heterotopic ossification of the normal bone cortex or parosteal bone. The etiology of BPOP is unclear and may be related to trauma. In most BPOPs, the lesion is not connected to the medullary cavity. Here we report an atypical case, characterized by reversed features compared to the typical BPOP, which demonstrated continuity of the lesion with the cavity. Case presentation An 11-year-old female child had a slow-growing mass on her right wrist for 8 months with forearm rotation dysfunction. Plain X-rays showed an irregular calcified mass on the right distal ulna, and computed tomography (CT) showed a pedunculated mass resembling a mushroom protruding into the soft tissue at the distal ulna. The medulla of this lesion is continuous with the medulla of the ulna. A surgical resection of the lesion, together with a portion of the ulnar bone cortex below the tumor was performed, and the final pathology confirmed BPOP. After the surgery, the child’s forearm rotation function improved significantly, and there was no sign of a recurrence at 1-year follow-up. Conclusion It is scarce for BPOP lesions to communicate with the medullary cavity. However, under-recognition of these rare cases may result in misdiagnosis or inappropriate treatment thereby increasing the risk of recurrence. Therefore, special cases where BPOP lesions are continuous with the medulla are even more important to be studied to understand better and master these lesions. Although BPOP is a benign tumor with no evidence of malignant transformation, the recurrence rate of surgical resection is high. We considered the possibility of this particular disease prior to surgery and performed a surgical resection with adequate safety margins. Regular postoperative follow-up is of utmost importance, without a doubt.

Bizarre parosteal osteochondromatous proliferations, also known as Nora’s lesions, are rare benign tumors with a high recurrence rate. They are often difficult to identify because of their similar appearance to other tumors. We describe a 25-year-old healthy female patient with bizarre parosteal osteochondromatous proliferations in an uncommon location on the pelvic ilium, presenting with unique clinical findings of abdominal pain and femoral paresthesia and showing atypical radiographic findings. To the best of our knowledge, this is one of the very few cases ever reported in the literature of Nora’s lesion in this particular location and possibly the first case ever with this specific presentation. The lesions’ radiographic images, combined orthopedic and general surgery procedures, and histological analysis are detailed. The patient’s continued 4-year follow-up has demonstrated no symptoms or evidence of recurrence.

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 (BPOP) is a rare benign surface-based bone lesion that primarily occurs in the hands and feet of young and early middle-aged adults. The lesion presents as a firm, usually painless mass of variable duration. Radiographs reveal a well-defined, pedunculated or sessile mass arising from the cortical surface of bone without altering the architecture of the underlying cortex. On magnetic resonance imaging, BPOP shows low to intermediate signal intensity on T1-weighted images and variable signal intensity on T2-weighted images. Marked enhancement is often seen after intravenous contrast administration. Histologically, the lesion is composed of an admixture of cartilage, bone and fibrous tissue. Between the cartilage and bone is a characteristic basophilic stroma, so called \"blue bone\". Immunohistochemistry does not play a significant role in the diagnosis of BPOP. Cytogenetic studies have demonstrated recurrent chromosomal abnormalities, including t(1;17)(q32-42;q21-23), inv(7)(q21.2-22q31.3-32) and inv(6)(p25q15). Most recently, gene rearrangements of collagen type I alpha 1 chain ( ) or collagen type I alpha 2 chain ( ) have been identified in a significant subset of cases. Surgical resection is the treatment of choice for symptomatic BPOP, but its local recurrence rate is relatively high. This review provides an updated overview of the clinicopathological, radiological, cytogenetic and molecular genetic features of BPOP and discusses the differential diagnosis of this uncommon lesion.

Bizarre parosteal osteochondromatous proliferation (BPOP), also termed Nora lesion, is a rare, benign tumor most often located in the hands and feet. We herein present the second reported case of BPOP affecting the spine, an uncommon location. One year after surgical excision, the patient was pain-free and showed no evidence of recurrence. We reviewed a total of 323 cases of BPOP among 101 articles, providing the first systematic update on the latest knowledge of BPOP. The age of patients with BPOP ranges from 3 months to 87 years, peaking in the second and third decades of life. The hands are the most common location of BPOP (58.39%), followed by the feet (20.81%). Imaging features play a key role in the diagnosis of BPOP, but histopathologic diagnosis remains the gold standard. Differential diagnosis of BPOP should be based on the epidemiologic and clinical features as well as clinical examination findings. Surgical resection is the most extensively used treatment for BPOP. Recurrence is common (37.44%) and can be treated with re-excision. This article can deepen our understanding of BPOP and will be helpful for the diagnosis and treatment of BPOP in clinical practice.

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.Key pointsBizarre parosteal osteochondromatous proliferation (BPOP) is a benign surface-based bone lesion.Hands are the most common location, followed by long bones and feet.BPOP is a mineralized mass arising from the periosteal aspect of bones.Histologically, it is composed of a mixture of cartilage, bone, fibrous tissue.Treatment consists of surgical resection, but local recurrences are common.

Background Bizarre parosteal osteochondromatous proliferation (BPOP), first described by Nora et al. in 1983 and therefore termed “Nora’s lesion”, is a rare lesion that occurs in the short bones of the hands and feet and eventually presents as a parosteal mass. Reports of BPOP in the long bones are very rare. A benign disease, BPOP does not become malignant, although a high rate of recurrence following surgical resection is reported. Because of its atypical imaging findings and histopathological appearance, a BPOP might be misdiagnosed as a malignant tumor such as an osteochondroma with malignant transformation, a parosteal osteosarcoma, or a periosteal osteosarcoma. Case presentation A 58-year-old woman complained of left ulnar wrist pain at the time of her initial presentation. Plain x-rays showed ectopic calcifications in and around the distal radioulnar joint, which supported the diagnosis of subacute arthritis with hydroxyapatite crystal deposition. She was initially given a wrist brace and directed to follow-up, but her persistent pain required the administration of corticosteroid injections into the distal radioulnar joint. Increasing ulnar wrist joint pain and limited forearm pronation and wrist flexion necessitated computed tomography and contrast-enhanced magnetic resonance imaging. BPOP was diagnosed based on the preoperative imaging studies, and a resection of the lesion was performed along with the decortication of the underlying the cortical bone to reduce recurrence rates. The diagnosis of BPOP was confirmed by pathologic examination. Two years after surgery, the patient has no subsequent pain complaints and an improved range of motion. Conclusions BPOP affecting the distal end of the ulna is exceedingly rare. Because BPOP was diagnosed primarily based upon preoperative imaging findings in our patient, decortication of the underlying cortical bone was performed to reduce recurrence rates. Further careful follow-up in these patients is essential, despite the non-recurrence of the lesion.