The Ivory Vertebra Sign

Ivory

The ivory vertebra sign is seen at conventional radiography and refers to an increase in opacity of a vertebral body that retains its size and contours, with no change in the opacity and size of adjacent intervertebral disks. The increased opacity may be diffuse and homogeneous and involve most or all of the vertebral body, giving it a white appearance as opposed to the normal or possibly osteoporotic appearance of the rest of the vertebral column.

The radiologic finding of a “white” vertebral body is observed in various conditions, each with its own mechanism of producing the classic appearance of the ivory vertebra sign. Osteoblastic metastases elicit a sclerotic response. This stimulation of osteoblasts results in the patchy replacement of vertebral body spongiosa with dense and amorphous bony mass that may become confluent. In a similar manner, certain lymphomatous deposits elicit marked osteoblastic response in the spongiosa, thereby resulting in bone formation and diffuse homogeneous sclerotic change. These lymphomatous foci involve the vertebral body through either hematogenous spread or contiguous invasion from adjacent lymph nodes. Another explanation is Paget disease, a condition in which simultaneous atrophy of the spongiosa and coursening of the vertical trabeculae can simulate an ivory vertebra.


Paget disease, however, usually causes expansion of the vertebral body contour, thereby limiting the ability of a vertebra affected by Paget disease to fully conform to the definition of an ivory vertebra. Reactive bone formation that occurs in response to stress on weakened bone, similar to the way a callus develops in a healing fracture, can give the appearance of an ivory vertebra; this process is termed idiopathic segmental sclerosis.

The ivory vertebra sign can be seen in both adults and children. In children, the finding is much less common and is typically the result of lymphoma, usually Hodgkin lymphoma. Even less frequently, children may have osteosarcoma, metastatic neuroblastoma, medulloblastoma, or osteoblastoma that involves a vertebral body and causes increased opacity. A few cases of Ewing sarcoma with dense vertebral bodies have been reported. In such cases, while the tumor itself is lytic, the reactive bone formation can be exceptionally opaque.

In adults, numerous conditions are responsible for the appearance of an ivory vertebra. Traditionally, the ivory vertebra sign has been associated with metastatic disease, especially carcinoma of the prostate or breast, and occasionally with osteosarcoma, carcinoid, Paget disease, and lymphoma, particularly Hodgkin lymphoma.

Carcinoma of the breast or prostate commonly results in osteoblastic metastases. A radiopaque vertebral body at one or more vertebral levels in an elderly man is most compatible with a diagnosis of metastatic disease, commonly as the result of prostate carcinoma. Other metastatic tumors, including lymphoma, must be considered along with more rare lesions, such as plasmacytoma, chordoma, or primary bone sarcomas. Metastatic cancer involving the spine usually manifests at several vertebral levels; however, solitary lesions in patients with breast carcinoma are not uncommon.

Lateral radiograph shows uniformly increased opacity of entire T7 vertebra (arrow), with retention of vertebral body size and contour. Incidental note is made of loss of height at T8 vertebra.

Transverse computed tomographic scan at level of T7 vertebra demonstrates increased opacity involving nearly the entire vertebral body.                       

Paget disease can give the appearance of an ivory vertebral body, but, more often, the disease is characterized by the “picture frame” vertebral body. The “picture frame,” “double contour,” or “windowed” vertebral body of Paget disease shows increased overall opacity, with sclerosis most marked at the periphery, and a relatively lucent center owing to atrophy of the spongiosa. The trabecular bone is thickened, and increased anteroposterior and lateral dimensions result in overall bone expansion. In Paget disease, the increased size of the vertebral body is a distinct appearance and usually allows differentiation of this disease from the other causes of the ivory vertebra sign.

Paget disease occurs in an older age group and is usually polyostotic. It has been suggested that idiopathic ivory vertebra, which is defined as an ivory vertebra for which no apparent cause is found and for which the appearance remains unchanged over time, may be attributable to asymptomatic Paget disease of bone. Definitive histologic evidence of the condition, however, is lacking.

Osteomyelitis is known to produce sclerosis in a vertebra during the healing phase, but this condition rarely involves a single vertebra. Usually, erosive change is present at the margins of the intervertebral disk and helps to guide diagnosis.

The ivory vertebra sign has numerous causes. While clinical settings will vary, and a list of causes is available, most causes of the ivory vertebra sign are rare. In adults, three conditions should generally be considered: metastatic cancer, Paget disease, and lymphoma.