"Vacuum" phenomena relate to the accumulation of gas, principally nitrogen, in crevices within the intervertebral disk or vertebra. Their appearance does not uniformly indicate "degenerative" disk disease (primary intervertebral osteochondrosis), as gaseous collections may accompany other processes (vertebral osteomyelitis, Schmorl node formation, spondylosis deformans, vertebral collapse with osteonecrosis) affecting the disk and adjacent vertebral bodies. The location and appearance of the "vacuum" phenomena are helpful indicators as to the precise nature of the spinal disorder.
Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease (CPPD) (pseudogout) are outlined in an investigation of 85 patients with definite or probable disease and available cadaveric and human surgical material. Pyrophosphate arthropathy produced distinctive roentgenographic abnormalities with were most frequent in the knee, wrist and metacarpophalangeal joints. Although the alterations superficially resembled osteoarthritis, they were frequently more severe and progressive with extensive fragmentation of bone, causing intra-articular osseous bodies. Pyrophosphate arthropathy occurred in unusual locations, such as the radiocarpal compartment of the wrist, elbow, and patellofemoral compartment of the knee. These characteristics allow the radiologist to suggest a probable diagnosis of CPPD even in the absence of articular calcification.
Cartilaginous (Schmorl's) nodes are related to prolapses of intervertebral disk material into the vertebral body. These nodes can be produced by any process which weakens either the cartilaginous plate covering the superior and inferior surfaces of the vertebral body or the subchondral trabeculae of the vertebra. Such processes include juvenile kyphosis, trauma, metabolic and neoplastic disorders, and degenerative disk disease. Radiographic abnormalities include indentations of vertebral outline and radiolucencies within the vertebral body with varying degrees of sclerosis. These can be readily differentiated from other vertebral alterations such as "butterfly", "fish", and "H" vertebrae.
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