Imaging description

Labyrinthitis ossificans (LO) is a disease process that is most often a sequela of purulent inflammation of the inner ear that results from bacterial meningitis. Pathologic ossification of spaces ensues within the lumen of the bony labyrinth and cochlea that can progress to new bone formation. The cochlea is most commonly involved, and early changes are often observed in the scala tympani of the basal turn. The ossification then spreads to the cochlear apical turn.

The course of progression has been divided into three characteristic stages: acute, fibrous, and ossification [1]. The acute stage is characterized by purulent inflammatory exudate that fills the perilymphatic spaces (Fig. 62.1). The second stage, or stage of fibrosis, consists of fibroblast proliferation within the perilymphatic spaces. The third stage, of ossification, is characterized by osteogenesis (Fig. 62.2).

In the early stages, CT is generally unrevealing and can be false negative. However, MRI may be able to demonstrate early changes within the membranous labyrinth that are not appreciated on CT. High-resolution, fast spin-echo, T2-weighted MRI can demonstrate the loss of normal hyperintensity of membranous labyrinth even in the early stages of LO (Fig. 62.3) [2].

In the later stages of LO, high-resolution temporal bone CT (HRCT) is extremely valuable in demonstrating the extent of ossification and for treatment planning. On occasion, a very extensive ossification can result in virtually complete obliteration of the membranous labyrinth and can be confused with congenital otic dysplasia (Fig. 62.4).