A unique presentation of the rare Nora's lesion, symptomatic bizarre parosteal osteochondromatous proliferation: A case report

Abstract

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.

Keywords: Nora’s lesion; bizarre parosteal osteochondromatous proliferation; ilium; unique presentation.

Figure 1.

(a–c) Axial, sagittal, and coronal computed tomography slices of the mass protruding from the right ilium. The red arrow shows the small medullary continuity at the base of the tumor (green star = BPOP, yellow arrow = psoas muscle, orange circle = colon, blue rectangle = kidney). BPOP: Bizarre parosteal osteochondromatous proliferation.

Figure 2.

(a and b) Magnetic resonance imaging T1 and T2 images of the lesion (green star = BPOP, yellow arrow = psoas muscle, orange circle = colon, blue rectangle = kidney). BPOP: Bizarre parosteal osteochondromatous proliferation.

Figure 3.

View of the lesion through the incision over the posterior right ilium. The patient was lying on her left side (position and direction labeled). The head of the BPOP tumor is visualized (arrow). BPOP: Bizarre parosteal osteochondromatous proliferation.

Figure 4.

Retractors holding the incision open as the BPOP (a star is next to the base of the tumor) is marginally excised with an osteotome. BPOP: Bizarre parosteal osteochondromatous proliferation.

Figure 5.

The fully excised Nora’s lesion before being sent to pathology analysis.

Figure 6.

Panoramic view: Mixture of cellular cartilaginous tissue and bone (H& E, original magnification × 12.5).

Figure 7.

Bizarre binucleated chondrocytes (H& E, original magnification × 100) (red arrow indicates example).

Figure 8.

Characteristic transition from one tissue type to another (chondro-osseous metaplasia), resulting in the formation of the “blue bone” (H& E, original magnification × 40).