Disc Calcification

► [Calcific deposits within the intervertebral disc tissue]

Calcification of the intervertebral disc can be isolated or occur in the context of systemic disorders, including degenerative, metabolic and syndromic diseases (Weinberger and Myers 1978). As a rule of thumb, and regardless of the chemical nature of the deposit, multiple intervertebral discs are involved with systemic and metabolic disorders, whereas focal disc involvement basically occurs in degenerative disease of the spine of the elderly, and in idiopathic disc calcification of children. In degenerative disease of the spine, prominent involvement of the intervertebral disc (intervertebral osteochondrosis) with aging results in progressive dehydration and loss of the elastic properties of the nucleus pulposus, with desiccation, volume loss, fibrosis, vacuum phenomena, and calcific deposits in the anulus fibrosus, nucleus pul-posus, and cartilaginous end-plates. The midthoracic and lumbar intervertebral discs are the most commonly involved. Calcific deposits associated with degenerative disease in the elderly are asymptomatic per se, and they tend to be permanent (Resnick and Niwayama 1995). Idiopathic intervertebral disc calcification of children has a peak incidence around 8 years of age and affects girls and boys with equal frequency. Calcification usually involves one intervertebral disc, but multiple locations can also occur. The cervical spine is the most typical site of involvement (Fig. 3.72 a,b), especially at C6-7, but cases of thoracic and lumbar involvement are not rare. The onset of symptoms is abrupt. Neck pain, stiffness, spasm torticollis and reduced range of motion are common complaints, while dysphagia is rare (Coventry 1970). Fever is seen in about one-third of patients. Leukocytosis and elevation of the white cell count can also be present. At the involved site, calcification typically affects the nucleus pulposus while sparing the annular ligament and is usually associated with disc space expansion. The calcified nucleus pulposus may herniate anteriorly into the prevertebral soft tissues or posteriorly into the spinal canal. The etiology is unknown. A clinical history of antecedent trauma (Smith et al. 1977) and inflammatory or infectious disease (Pattisapu et al. 1987) has been reported. Differences from spondylodiscitis are fairly evident in that the latter, unlike idiopathic discal calcification, is associated with disc space narrowing, vertebral erosion, and absence of disc ossification. The natural history is typically one of complete clinical and radiographic resolution within a time frame of 3-6 weeks. Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is the designation for a disorder of middle-aged and elderly patients, which is characterized by the presence of Ca2P2O7.2H2O crystals in or around the joints. On clinical grounds, this disorder can either mimic gout (pseudogout), rheumatoid arthritis (pseudorheumatoid arthritis), degenerative joint disease (pseudo-osteoarthritis),or neuropathic osteoarthropathy (pseudo-neuropathic osteoarthropathy) (Resnick and Niwayama 1995). CPPD crystal deposition disease occurs as a sporadic or a hereditary (van der Korst et al. 1974) disorder, or in association with other disorders, notably hyperparathyroidism, familial hypocalciuric hyper-calcemia, hemochromatosis, hypophosphatasia, Bartter syndrome, gout, amyloidosis, corticosteroid therapy, and alkaptonuria (Doherty and Dieppe 1988). CPPD crystal deposits occur primarily within the joint (articular cartilage, synovium, and capsule), but periarticular tissues (tendons and ligaments) are also often affected. Sites of involvement include, in order of declining frequency: elbow, metacarpophalangeal joints, glenohumeral, wrist, knee, ankle, symphysis pubis, hip, and cervical spine (Resnick et al. 1977). In the spine, calcific deposits occur most commonly in the outer fibers of the anu-lus fibrosus in the form of vertical, peripherally located thin layers. However, other patterns of calcification are encountered, including primary ossification of the nucleus pulposus (familial CPPD crystal deposition disease) and mixed involvement of both the nucleus pulposus and anulus fibrosus (Fig. 3.73), with or without cartilaginous nodes extending through the vertebral end-plates. Calcifications may also be seen within the spinal ligaments (ligamen-tum flavum, anterior and posterior longitudinal ligament, interspinous and supraspinous ligaments) and within the articular cartilage, synovium, and capsule of the apophyseal joints (Resnick and Pineda 1984).

Fig. 3.72 a, b. Idiopathic disc calcification in a 9-year-old boy evaluated because of neck pain and stiffness with onset 2 weeks after a febrile upper respiratory infection. a An-teroposterior and b lateral radiograms revealed calcification of the intervertebral disc at C5-6. Absence of disc space narrowing and vertebral erosion differentiates this condition from discitis

Fig. 3.72 a, b. Idiopathic disc calcification in a 9-year-old boy evaluated because of neck pain and stiffness with onset 2 weeks after a febrile upper respiratory infection. a An-teroposterior and b lateral radiograms revealed calcification of the intervertebral disc at C5-6. Absence of disc space narrowing and vertebral erosion differentiates this condition from discitis

Supraspinous Ligament CalcificationDisc Calcification
Fig. 3.73. Calcium hydroxyapatite crystal deposition. 62-year-old man. Observe calcific deposits involving the anulus fibro-sus and nucleus pulposus

Calcification of the intervertebral disc can occur in association with those conditions that lead to spinal ankylosis, including alkaptonuria, ankylosing spondylitis, juvenile chronic arthritis, diffuse idiopathic skeletal hyperostosis, Klippel-Feil syndrome, and surgical fusion of the spine. Discal calcification is the most characteristic spinal abnormality in alkaptonuria (OMIM 203500), a hereditary metabolic disorder characterized by accumulation of homo-gentisic acid attributed to absence of the enzyme homogentisic acid oxidase (Lagier and Sit'aj 1974). The calcific deposits have a diffuse distribution, with multiple spinal levels involved at the same time (the lumbar and thoracic spine are the most common sites). The inner fibers of the anulus fibrosus or the whole disc are involved. Osteoporosis, small or absent osteophytes, disc space narrowing, and vertebral fusion are additional spinal findings in this disorder (Guhl et al. 1981). Discal calcification, with progressive ossification and fusion of contiguous vertebral bodies, can also be observed in ankylosing spondylitis (OMIM 106300), in which, however, the presence of thin and vertically oriented syndesmophytes allows correct identification.

Intervertebral disc calcification in the thoracic spine may be observed in Aarskog syndrome (OMIM 305400). Other spinal features in this disorder include cervical anomalies (hypoplasia,synostosis,and spina bifida occulta), mild laxity of the C1-2 liga-mentous structures, and scoliosis. Intervertebral calcification also occurs in Cockayne syndrome (OMIM 216400), a condition in which spinal involvement consists of ovoid vertebral bodies with anterior notching, biconvex vertebral bodies, scalloping and posterior wedging of the vertebrae, and thoracic kyphosis.

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