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FISH VERTEBRAE.

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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 L a Jolla Village Dr.,
San Diego, CA 92161.
Submitted for publication February 11, 1982; accepted
February 12, 1982.
Arthritis and Rheumatism, Vol. 25, No. 9 (September 1982)
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 a n 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
1074
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
RESNICK
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. 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.
RESNICK
1076
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).
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.
REFERENCES
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.
1. Resnick D: The “rugger jersey” vertebral body. Arthritis
Rheum 24:1191-1194, 1981
2. Parfitt AM, Duncan H: Metabolic bone disease affecting
the spine, The Spine. Edited by RH Rothman, FA
Simeone. Philadelphia, WB Saunders Co, 1975, p 599
3. Hurxthal LM: Measurement of anterior vertebral compressions and biconcave vertebrae. Am J Roentgen01
103:635-644, 1968
4. Dietz GW, Christensen EE: Normal “cupid’s bow”
contour of the lower lumbar vertebrae. Radiology
121 :577-580, 1976
5. 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 27:233-247, 1945
6. Resnick D, Niwayama G: Intravertebral disk herniations:
cartilaginous (Schmorl’s) nodes. Radiology 12657-65,
1978
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