Chapter 2 Cysts and Other Benign Lesions
Langerhans cell histiocytosis (LCH) is an abnormal histiocyte proliferation producing granulomatous skeletal lesions. It has not been confirmed whether LCH is a real tumor or inflammatory process. Clinically, it is considered a malignant lesion, because it has a tendency toward local recurrence.
Aneurysmal bone cysts are benign expansile lesions characterized by small and large cavernous spaces filled with clotted-blood fluid. They may arise de novo, or they may secondarily complicate other benign and malignant bone tumors that have undergone hemorrhagic cystic change.
Spinal synovial cysts are cystic masses involving the spinal canal as a result of degenerative changes in the facet joints, trauma, metaplasia, the presence of developmental rests, or excess stress inflicted at the facet joints coupled with the herniation of synovial tissue.
Fibrous dysplasias are bony lesions characterized by the metaplastic replacement of the medullary component of one bone (monostotic), or less commonly of several bones (polyostotic), with fibrous tissue and irregular osteoid formation. This disorder involves multiple symptoms.
Infectious lesions of the vertebral body (bacterial or tuberculous) are another category that should be differentiated from the metastatic or primary bone tumors. Bacteria enter the bone marrow through vascularized subchondral bone adjacent to the endplate.
Spinal extradural arachnoid cysts are thought to be an extradural extension of an arachnoid membrane and cerebrospinal fluid (CSF) through a small defect in the dura. Several theories have been suggested about the pathogenesis of the lesion and the mechanism of cord compression.
Fig. 2-4 Axial MR image. Low signal infiltrative lesion is shown in the sacrum on T1WI (left), intermediate signal on T2WI (middle), and homogeneous enhancement (right). Epidural mass formation and dural sac compression are observed.