BIZARRE PAROSTEAL OSTEOCHONDROMATOUS PROLIFERATION (NORA'S LESION) A REPORT OF 4 CASES J. BEN NASR, M. CHELLI BOUAZIZ, W. TURKI, L. ABID, MH. JAAFOURA, MF. LADEB MUSCULOSKELETAL : MK 24

INTRODUCTION Bizarre parosteal osteochondromatous proliferation (BPOP) was first described by Nora in 1983 Occurs mostly on small bones of hands and feet Rare benign lesion that can be confused with other benign and malignant conditions We present four cases of BPOP outlinig clinical, radiological and histological findings.

PATIENTS AND METHODS Retrospective study of four radio-clinical observations of histologically confirmed NORA's lesions, collected in our insitution 1 man and 3 women aged from 24 to 52 years The patients were investigated by radiographs (n = 4), ultrasound (n = 2), CT (n = 1) and MRI (n = 1)

Case 1 : 52 year old male 5 year history of mass on the palmer aspect of the right index No history of trauma CASE REPORTS

Fig 1b: Ultrasound of the right index: calcified lesion without modification in adjacent soft tissues. Fig 1a : Anteroposterior and lateral radiographs of the right index show a juxta-cortical calcified lesion of the middle phalanx with adjacent cortical erosion

Case 2 Case 2 A 24 year-old woman No significant medical history Nine months history of a hard mass of the second phalanx of her right medius No concept of trauma CASE REPORTS

Fig 2a : Lateral radiograph of the right medius shows a calcified well circumscribed lesion, developed at the palmar aspect of the middle phalanx base, with no adjacent bone or soft tissue abnormality

Fig 2b: High resolution ultrasound of the right medius in transversal view: calcified lesion surrounded by a thin hypoechoic cap Fig 2c: Transversal CT view of the right hand in bone algorithm: Surface bone lesion with large cortical base. There is no continuity between the lesion and the underlying bone cortex

Fig 2f : Cartilaginous prolifération made of chondrocytes with irregular morphology (bizarre cells) (HE x400) Fig 2e : Tumoral proliferation with osseous( ), cartilaginous ( ) and fibrous ( )components( HE x 200) Fig 2d: Gross pathology. Well circumscribed pediculated mass, of hard consistance and white greyish colour

Case 3 : A 38 year old woman Swelling and discomfort affecting her right forefoot. No significant past medical history nor history of trauma On examination, there was a fusiform swelling regarding the proximal phalanx of the third right toe. CASE REPORTS

Fig 3: Antero posterior radiograph of the right foot shows an ossified mass developed from the proximal phalanx of the third toe

Case 4 : Woman of 45 years, tailor, right-handed History of benign breast tumor Swelling and pain in the distal phalanx of the right medius CASE REPORTS

Fig 4a: Lateral radiograph of the right medius shows a calcified bone surface lesion developed from the palmar surface of the distal phalanx with soft tissue swelling but no adjacent bone abnormality

Fig 4b: Sagittal MRI view of the right hand on T1 W sequence, T1W sequence after intravenous Gadolinium injection and T2 W sequence.The lesion shows a homogenous low T1 signal and high T2 Signal with moderate enhancement after intravenous Gadolinium injection.

Fig 4c: Microscopic view(HE x 200) showing bone trabeculae associated with fibrous tissue Fig 4d: Microscopic view (HE x 400) showing chondroïd tissue made of chondrocytes of irregular size sometimes binucleated ( )

RESULTS The lesions were palmar (3 cases) and plantar (1 case) swelling, painful in 3 cases Radiographs showed a calcified juxtacortical well marginated mass, of less than 3 cm, attached to the external face of the cortical bone of a phalanx High resolution ultrasound showed a calcified lesion surrounded by a thin hypoechoic cap On CT, the lesions had a wide base of implantation on bone. MRI showed a juxtacortical lesion, hypointense on all sequences with an intralesional enhancement

RESULTS All patients underwent excisional biopsy of the lesion Histopathological examination confirmed the diagnosis in all cases Two patients were lost to follow up after surgery The other two had a postoperative follow-up of 6 and 18 months, without clinical or radiological recurrence

BPOP is a benign and rare surface lesion of bone BPOP affects males and females equally There can be a wide range of age presentation, though the lesion is most common in the third and fourth decade Epidemiological features : DISCUSSION

Usually affects the proximal and middle phalanges, and the metacarpal or metatarsal bones The hands are 4 times more commonly affected than the feet Unlike subungual exostosis, this lesion is rarely found on distal phalanges BPOP is less commonly found in other sites and have been reported in unusual locations such as the humerus and the clavicle Location : DISCUSSION

The typical clinical presentation is a painless swelling that grows over a period of months to years On examination, BPOP is a firm mass, usually small, ranging from 0.4 to 3 cm in diameter and do not involve the overlying skin Joint motion may be limited when the lesion is located at the end of a bone Clinical features : DISCUSSION

BPOP is a well-marginated, calcified or ossified mass arising directly from the cortical surface of the underlying bone It is generally attached by a broad base and the underlying cortex is intact There is no periosteal new bone formation. However, cortical erosion has been reported Radiographs : DISCUSSION

Fine cut Computed Tomography scan shows a mass with well defined margins, intensely calcified or ossified, arising from the cortex of the affected bone CT is, better than radiographs in showing the absence of continuity between the cortex and the medullar cavity of the bone and the absence of cortical flaring in this affected bone CT Scan : DISCUSSION

BPOP displays homogenous low signal intensity on T1 weighted sequences with uniform enhancement following the IV administration of gadolinium On T2 weighted images, the lesion has a high signal, slightly increased signal centrally compared with its periphery being of higher signal intensity. MRI show neither periosteal reaction nor medullary involvement but normal underlying bone and adjacent soft tissues MRI : DISCUSSION

BPOP has an atypical histological appearance The lesion contains highly cellular, disorganized and irregular cartilage, proliferation of bizarre fibroblasts and disorganized bone with spindle shaped fibroblasts in the intertrabecular space The presence of an unusual form of calcified cartilage that stains blue on hematoxylin and eosin (H & E) stain is characteristic Pathological findings : DISCUSSION

Mitotic figures are often seen, but neither atypical mitosis nor cytological atypia is seen BPOP may also be confused with osteochondromas but osteochondromas are rare in the hands (4% of osteochondromas) Moreover, in the lesion of Nora, there is no continuity between the medullary canal and cortical bone with the underlying bone bone Pathological findings : DISCUSSION

 Florid reactive periostitis  Ossified hematoma  Myositis ossificans  Stress fracture with extensive callous formation  Parosteal osteosarcoma  Peripheral chondrosarcoma Differential diagnosis : DISCUSSION

No treatment is required if a BPOP is asymptomatic, as the lesion is benign If the patient is symptomatic (pain or compromised function), definitive treatment is by surgical excision with wide margins Treatment : DISCUSSION

DISCUSSION BPOP has a remarkable tendency to recur(51%) Time interval between excision and local recurrence ranges from 2 months to 2 years No malignant transformation, metastases or deaths have been described in patients with BPOP Because of its high local recurrence rates and the lack of adjuvant therapy options, Nora's lesion requires long-term follow up Local Recurrence :

CONCLUSION The NORA’s lesion is benign Imaging and and histological features allow the distinction of this rare entity from true bone tumors