Fine Configuration of Thoracic Type II Meningeal Cysts: Macro- and Microscopic Cadaveric Study Using Epoxy Sheet Plastination.

STUDY DESIGN A cadaveric study OBJECTIVE.: The aim of this study was to analyze the in situ macro- and microscopic configuration of the type II cyst and its anatomic relationship with surrounding structures. SUMMARY OF BACKGROUND DATA The lack of consensus of surgical strategy to manage symptomatic type II meningeal cysts (Tarlov cysts) is because our knowledge of type II cyst anatomy remains incomplete. It has been assumed that the cyst communicates with the subarachnoid space via microconnections. Till date, however, no direct evidence demonstrates the existence of the microconnections, although delayed contrast filling of type II cysts is commonly observed in CT myelography. METHODS Three type II meningeal cysts analyzed in this study were incidentally found in one of 16 plastinated spines. The spine was from an 89-year-old female cadaver and plastinated as a set of 164 transverse sections with a thickness of 2.5 mm. The sections were examined under a stereomicroscope. RESULTS Three type II cysts were in the thoracic spine and had a common feature that a clearly identifiable cyst neck connected the cyst body to the subarachnoid space. The dorsal root of the spinal nerve was centered in the cyst neck but spread over the cyst body or traversed the cyst cavity. The meningeal opening of the cyst was located above the inferior border of the vertebral pedicle, thus, the cyst neck hugged around the pedicle and sharply turned inferolaterally into the intervertebral foramen. The cyst body was halted by the dorsal ganglion. CONCLUSION This study reveals in situ macro- and microscopic configuration of the type II cyst and its relationship with the structures and suggests that it may be feasible to localize and ligate the cyst neck for surgical management of type II cysts. LEVEL OF EVIDENCE 3.