[Histopathology of congenital pseudarthrosis of tibia]

To investigate the histopathology, origin, and etiology of congenital pseudarthrosis (CPT).

Specimens of periosteum from 28 CPT cases, 20 cases of traumatic pseudarthrosis (TP), 10 cases of fibromatosis, and 10 normal controls were examined. The pathological changes were observed by electron microscopy and confocal microscopy. The expression of alpha-smooth muscle (SM) actin, vimentin, desmin, bone morphogenic protein (BMP), interleukin (IL)-1, IL-6, tumor necrosis factor-alpha (TNF-alpha) and base fibroblast growth factor (b-FGF) were detected by histochemistry and immunofluorescence chemical staining. Chromosomal karyotype was examined among 11 cases of CPT.

(1) Electron microscopy showed that the periosteum and soft tissue between the broken ends in CPT were all dense fibrous connective tissue abundant in cells, including fibroblasts, myofibroblasts, etc. (2) The chief collagen element was type I collagen in normal periosteum and was type III collagen in periosteum of patients with CPT and fibromatosis (P < 0.025). (3) Vimentin was positive and desmin was negative in all specimens. The expression of alpha-SM actin was higher in specimens from CPT and fibromatosis than in specimens from normal control and TP (P < 0.01). The expression of BMP was higher in normal periosteum and TP than in the periosteum of CPT and fibromatosis (P < 0.05). The expression of IL-1, IL-6, TNF-alpha, b-FGF was higher in the periosteum of CPT and TP (P < 0.01). (4) The chromosomal karyotype of all CPT patients was normal 46XY or 46XX.

(1) Neurofibromatosis is probably not the etiological factor of CPT. (2) CPT is a kind of invasive fibromatosis located in periosteum. (3) Abnormal expression of many kinds of cytokine and high expression of type III collagen play an important role in the pathogenesis of CPT. (4) The main pathology of CPT is hyperplasia of fibroblasts, thus causing thickening of periosteum, contractible circinate coarctation, and compression of tibia and surrounding tissues. (5) The chromosomal karyotype of patients with CPT is normal.