Congenital Syphilis — Wimberger Sign

A 6-week-old female infant born to an unbooked mother presents with failure to thrive, persistent mucopurulent nasal discharge ("snuffles"), a maculopapular desquamating rash on the palms and soles, and hepatosplenomegaly. The infant is irritable on handling. Maternal serology is VDRL-reactive with high titer and TPHA-confirmed; infant serology shows a non-treponemal titer fourfold higher than the mother's and reactive IgM FTA-ABS. Long bone radiographs of both lower limbs demonstrate the radiological finding marked **B** in the diagram. Which of the following best describes the pathological process underlying the radiological sign marked **B**?