Imaging description

Perineural spread (PNS) is a mechanism whereby tumor, or another pathological condition, spreads along loose connective tissue of the perineurium. It is a common complication of head and neck cancers [1]. Although any cranial nerve can be involved by PNS, it is most commonly observed along the branches of cranial nerves V and VII and their anastomotic branches.

Direct imaging signs include enlargement, irregularity, and excessive enhancement of the cranial nerves and their branches (Figs. 60.1, 60.2). With high-resolution MR imaging, the nerve itself can frequently be visualized (Fig. 60.1B). Within the neural foramina and bony canals, the nerve is normally seen surrounded by a small perineural venous plexus. Care should be taken to avoid mistaking this normal plexus for perineural enhancing tumor. After the nerve exits the neural foramen or canal, it is generally seen surrounded by fat. It is important to pay close attention to normally observed fat pads along the neural foramina on unenhanced T1-weighted images. Presence of tumor along the cranial nerves obliterates the normally observed high T1 signal of these fat pads (Table 60.1). In advanced cases, enlargement or destruction of neural foramina and canals can be seen. Continued retrograde tumor spread can involve the cisternal segments of the cranial nerves and, ultimately, the brainstem.