Abstract
Introduction: Bizarre parosteal osteochondromatous proliferation (BPOP), commonly referred to as Nora's lesion, is a rare benign neoplasm arising from the cortical surface of bone. It is characterized by distinctive clinicoradiologic and histopathologic features and by a non-negligible propensity for local recurrence. Ex tracranial, non-acral localizations-including involvement of the malleolar region-are uncommon and may represent a source of diagnostic uncertainty.
Case Presentation: We report the case of S.G., a 56-year-old male, who presented for clinical evaluation due to a progressively enlarging swelling of the left lateral malleolus, with an onset approximately two months prior to presentation. Imaging assessment, including conventional radiography and computed tomography, demonstrated a parosteal osteochondromatous lesion adherent to the underlying cortical bone, without con tinuity with the medullary cavity and without evidence of infiltration of the adjacent soft tissues. The overall radiologic features were suggestive of BPOP. The case was retrospectively analyzed through integration of clinical and imaging findings, with appropriate consideration of the principal differential diagnoses.
Discussion: Bizarre parosteal osteochondromatous proliferation is regarded as a histologically benign yet locally active lesion, with a biological behavior that may, in certain cases, mimic that of aggressive surface bone neoplasms. This potential for misinterpretation is particularly pronounced in anatomically atypical sites, such as the malleolar region, where limited familiarity and overlapping imaging features may further compli cate diagnostic assessment. In such contexts, a multidisciplinary approach is essential, grounded in careful radiologic-pathologic correlation to ensure diagnostic accuracy. Complete surgical excision with clear mar gins represents the treatment of choice. Nevertheless, the recurrence rates reported in the literature are not negligible, underscoring the need for adequate resection and structured postoperative surveillance.
Conclusions: Although rare, malleolar involvement by Nora's lesion falls within the recognized topographic spectrum of BPOP. Awareness of this potential presentation is critical to avoid overestimation of malignant potential and the consequent adoption of unnecessarily aggressive therapeutic strategies. The documentation of additional well-characterized cases will be instrumental in refining our understanding of the clinicobiologi cal behavior of this entity and in optimizing its diagnostic and management pathways.
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