FISH VERTEBRAE RADIOLOGIC VIGNETTE DONALD L. RESNICK

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1 ~ 1073 RADIOLOGIC VIGNETTE FISH VERTEBRAE DONALD L. RESNICK The term fish verfebru is applied to a vertebral body that has an abnormal shape characterized by biconcavity due to depression of its superior and inferior borders. The depression is variable in extent but predominantly occurs in the central aspect of the borders, with relative sparing of the anterior and posterior margins. The precise origin of the term is frequently debated; some observers contend that the altered vertebral body resembles the shape of a fish, but others note the similarity of the resulting biconvexity of the adjacent intervertebral discs to that of a fish mouth. On radiographs of the spine of normal fish, a series of vertebral bodies (each possessing typical biconcavity) is revealed, indicating a more logical explanation for the designation fish vertebrae (Figure 1). What is normal in fish is certainly abnormal in humans! Biconcave deformity of the vertebral bodies is characteristic of disorders in which there is diffuse weakening of bone. Such disorders include osteoporosis (Figure 2), osteomalacia, osteitis fibrosa cystica (hyperparathyroidism), and Paget s disease. In these diseases, osseous deformity is the result of an expansive pressure of the intervertebral discs that leads to arch-like depression of the superior and inferior mar- From the Department of Radiology, Veterans Administration Medical Center and University of California, San Diego, CA. Donald L. Resnick, MD: Professor of Radiology, University of California, San Diego, and Chief, Radiology Service, VA Medical Center, San Diego, CA. Address reprint requests to Donald Resnick, MD, Chief, Radiology Service, VA Medical Center, 3350 La Jolla Village Dr., San Diego, CA Submitted for publication February 11, 1982; accepted February 12, gins of the vertebral body. These changes occur opposite the nucleus pulposus of the intervertebral disc; the bony rims at the edges of the vertebral bodies are stronger than the central segment and more resistant to this expansive pressure. On pathologic examination, it can be seen that the cartilaginous endplates covering the central aspect of the vertebral margins are thinned and stretched. Fish vertebrae are most prominent in the lower thoracic and upper lumbar regions of the spine. In the middle and upper portions of the thoracic spine where there exists a normal kyphosis, diffuse osseous weakening is associated with anterior collapse or wedging of vertebral bodies (see below). The identification of the precise disease process that leads to fish vertebrae is frequently possible by use of additional radiographic characteristics. Associated findings such as the rugger jersey appearance of renal osteodystrophy and the picture-frame appearance of Paget s disease are virtually diagnostic (1). The differentiation of osteoporosis and osteomalacia, however, based upon characteristics of the fish vertebrae can be difficult: osteomalacia is associated with uniform involvement of all vertebral bodies, which leads to depression of the superior and inferior borders to an equal extent with biconcave vertebral deformities that are smooth in outline; osteoporosis may affect one vertebral body and spare its neighbor, involve one border of a vertebral body to a greater degree than the other, and produce an irregular or crenated biconcave appearance (2). Furthermore, in osteoporosis, thinned but distinct subchondral bone plates at the top and bottom of the involved vertebral body and accentuation of the vertical trabecular pattern are characteristic (Figure 2). In some varieties of Arthritis and Rheumatism, Vol. 25, No. 9 (September 1982)

1074 RESNICK Figure 1. Fish vertebrae. On a frontal radiograph of the spine in a tuna, normal biconcave depressions involving the superior and inferior aspects of each vertebral body are revealed.

2 1074 RESNICK Figure 1. Fish vertebrae. On a frontal radiograph of the spine in a tuna, normal biconcave depressions involving the superior and inferior aspects of each vertebral body are revealed. osteoporosis, such as that associated with corticosteroid medication, exaggerated callus formation around the collapsed vertebral margins leads to radiodense bands at the top or bottom of the vertebral body (Figure 3). Fish vertebrae must be distinguished from radiographic artifacts, normal variants, and other pathologic alterations of the spine. Poor technique during lateral radiography in normal individuals can result in an oblique projection of the vertebral endplates and cause a false impression of discal ballooning and vertebral compression (3). This problem is accentuated in individuals with abnormal spinal curvature, such as scoliosis, in whom tangential radiographs of the vertebral bodies are difficult to obtain. A normal concavity on the inferior aspect of the third, fourth, and fifth lumbar vertebral bodies, termed the Cupid s bow contour, resembles the biconcave changes of fish vertebrae (4). When viewed from the front, parasagittal impressions on the undersurface of the vertebrae resemble a bow, pointing cephalad. On lateral views, the vertebral depressions are located posteriorly. Their cause is unknown, although they may be related to nuclear expansion produced by the turgor of the nucleus pulposus (5). Fish vertebrae should be differentiated from vertebrae with cartilaginous (Schmorl s) nodes. These nodes represent sites of intraosseous herniation of discal material (6) (Figure 4). Such herniation is allowed by disorders such as osteoporosis, osteomalacia, infection, and neoplasm that lead to weakening of the cartilaginous endplate and the subchondral bone plate. Radiographic findings include interruption of the subchondral white line and a radiolucent area in the vertebral body with surrounding bony sclerosis. The number, location, and size of the cartilaginous nodes are variable, depending on the specific underlying disease that is present. Fish vertebrae may be an associated finding. Biconcave vertebral bodies should also be differentiated from wedge-shaped and flattened (pancake) vertebrae. Wedging refers to a reduced height of the anterior border of a vertebral body in the presence of a normal posterior border. Wedge-shaped vertebral bodies are common in the midthoracic region in the area of the normal thoracic kyphosis (Figure 5). They may result from an acute compression injury to the normal spine or prolonged stress to the abnormal (i.e., osteoporotic) spine. Diffuse flattening of a vertebral body (pancake vertebrae) due to compression of the entire vertebral surface is commonly associated with intraosseous neoplasm (Figure 6) or discal pathology.

RADIOLOGIC VIGNETTE 1075 A Figure 3. Fish vertebrae in patient receiving corticosteroid medication.

the affected vertebrae is associated with radiodense bands. B Figure 2. Fish vertebra in osteoporosis.

are shown. Observe that the concavity (arrows) is more exaggerated on one side of the vertebral body than the other.

3 RADIOLOGIC VIGNETTE 1075 A Figure 3. Fish vertebrae in patient receiving corticosteroid medication. In addition to biconcave deformities involving the vertebral bodies, condensation of bone at the superior and inferior margins of the affected vertebrae is associated with radiodense bands. B Figure 2. Fish vertebra in osteoporosis. On a radiograph (A) and photograph (B) of coronal sections of two spines from cadavers with osteoporosis, typical fish vertebrae are shown. Observe that the concavity (arrows) is more exaggerated on one side of the vertebral body than the other. In addition, the white line that represents the subchondral bone plate is very distinct, and there is accentuation of the vertical trabecular pattern. These latter features are typical of osteoporosis.

4 1076 RESNICK A B Figure 4. Cartilaginous (Schmorl s) nodes. On a radiograph (A) and photograph (B) of sections from two different cadavers, cartilaginous node formation is shown. Observe interruption of the subchondral bone plate (arrows) with intraosseous herniation of portions of the intervertebral disc (arrowheads).

Wedge-shaped vertebral bodies. In this cadaver with osteoporosis, a lateral radiograph of the midthoracic spine reveals vertebral collapse, most extensive along the anterior surface of the spine.

5 RADIOLOGIC VIGNETTE 1077 Figure 6. Diffuse vertebral flattening (pancake vertebrae). In this cadaver with multiple myeloma, a radiograph of a coronal section of the spine shows diffuse flattening of affected vertebral bodies. Fragmentation is also apparent. Figure 5. Wedge-shaped vertebral bodies. In this cadaver with osteoporosis, a lateral radiograph of the midthoracic spine reveals vertebral collapse, most extensive along the anterior surface of the spine. In addition, cartilaginous nodes are apparent. REFERENCES 1. Resnick D: The rugger jersey vertebral body. Arthritis Rheum 24: , Parfitt AM, Duncan H: Metabolic bone disease affecting the spine, The Spine. Edited by RH Rothman, FA Simeone. Philadelphia, WB Saunders Co, 1975, p Hurxthal LM: Measurement of anterior vertebral compressions and biconcave vertebrae. Am J Roentgen : , Dietz GW, Christensen EE: Normal cupid s bow contour of the lower lumbar vertebrae. Radiology 121 : , Coventry MB, Ghormleu RK, Kernohan JW: Intervertebra1 disc: its microscopic anatomy and pathology: changes in the intervertebral disc concomitant with age. J Bone Joint Surg 27: , Resnick D, Niwayama G: Intravertebral disk herniations: cartilaginous (Schmorl s) nodes. Radiology , 1978

HYPEROSTOSIS AND OSSIFICATION IN THE CERVICAL SPINE

564 RADIOLOGIC VIGNETTE HYPEROSTOSIS AND OSSIFICATION IN THE CERVICAL SPINE DONALD RESNICK A variety of diseases can produce hyperostosis or ossification in the cervical spine. Included among these are