Paravertebral fibrous pseudotumor: Four cases of a distinctive tumefactive lesion overlapping with eosinophilic angiocentric fibrosis and tumoral erythema elevatum diutinum.

Eosinophilic angiocentric fibrosis (EAF) is a rare tumefactive fibroinflammatory disease with predilection for the upper respiratory tract, characterized by concentric (onionskin) fibrosis around small arterioles with variable intervening storiform fibrosis admixed with chronic inflammatory infiltrates rich in eosinophils. Erythema elevatum diutinum (EED), another autoimmunological disorder that mainly affects acral sites and extensor surfaces, is characterized by neutrophilic leukocytoclastic vasculitis. Rarely, older EED lesions may present as tumefactive nodular (pseudotumoral) fibrous masses closely mimicking EAF. We herein describe four patients (all males) aged 66-70 years who presented with large (median, 7 cm) tumor-like fibrous lesions in the paravertebral region not associated with a known clinical autoimmune disease. All cases were resected surgically with the suspicion of a neoplasm. They displayed a strikingly similar histological appearance with combined features of EAF and nodular fibrous EED. None had evidence of obliterative phlebitis or increased IgG4: IgG ratio. The etiology of this distinctive lesion and its predilection for the paravertebral area of males remains obscure. A distinctive tumefactive localized reaction to trauma caused by degenerative disease of adjacent vertebrae might be a possible explanation.