(Radiology. 1999;211:773-774.)
© RSNA, 1999
The Dense Metaphyseal Band Sign1
Scott A. Raber, MD
1 From the Division of Radiology, Charleston Naval Hospital, 3600 Rivers Ave, North Charleston, SC 29405-7769. Received January 20, 1998; revision requested February 19; revision received November 16; accepted January 7, 1999. Address reprint requests to the author.
Index terms: Bones, diseases, 40.27, 40.34, 40.521, 40.533, 40.581, 40.5832 • Bones, metaphyses
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APPEARANCE
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Dense metaphyseal bands, less commonly known as dense metaphyseal lines, transverse bands, or "lead lines," indicate radiopaque bone (thicker than the adjacent diaphyseal cortex) at the metaphysis of growing bone, particularly at the wrists and knees (Figs 1, 2).
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Figure 1. Anteroposterior radiograph of the wrist obtained in a 2-year-old boy reveals a dense metaphyseal band (arrow) in the distal radius, without flaring or cupping. The distal ulna is unremarkable. By excluding more serious causes, this finding was proved to be a normal variant.
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Figure 2. Anteroposterior radiograph of the knees in a 5-year-old girl reveals very dense metaphyseal bands in the distal femurs and proximal tibias (arrows) as well as in the proximal fibulas (arrowheads). This patient was encephalopathic and anemic and had a lead level of 60 µg/dL (2.898 µmol/L) at admission.
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EXPLANATION
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Normal metaphyseal endochondral bone growth (in the zone of provisional calcification) requires the maintenance of a delicate balance between osteoblastic bone deposition and osteoclastic bone remodeling (1). Whenever growing bone is subjected to toxic, metabolic, neoplastic, or infectious stressors, proper osteogenesis is compromised. Stress on growing bone leads to poor endochondral bone formation. In general, when the stress is eliminated, rapid deposition of new bone at the metaphysis produces dense bands.
The result of osseous lead poisoning effectively illustrates a specific example of how the dense metaphyseal band sign is formed. With lead toxicity, or plumbism, the lead ions deposit on the hydroxyapatite crystal but preferentially in the zone of provisional calcification. Lead inhibits osteoclastic remodeling, but it has no effect on osteoblasts. The result is an increase in the thickness and number of trabeculae at the metaphysis (2). The lead itself contributes very little to the metaphyseal density in plumbism. Whenever growing bone recovers from any pathologic insult or becomes lead poisoned, exuberant calcium deposition in the zone of provisional calcification yields dense metaphyseal bands.
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DISCUSSION
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The dense metaphyseal band sign enables a lengthy differential diagnosis. In order of decreasing frequency, the causes of a dense metaphysis include normal variance, plumbism, treated leukemia, healing rickets, other heavy metal (arsenic, bismuth, mercury) poisoning, recovery from scurvy, vitamin D hypervitaminosis, congenital hypothyroidism, hypoparathyroidism, and transplacental infections (eg, toxoplasmosis, rubella, cytomegalovirus, and herpes) (3–5).
The most common cause of a dense metaphysis is seen as a normal variant in healthy children. Following prolonged exposure to sunlight, especially after the winter months, abundant calcification occurs in the zone of provisional calcification. This phenomenon may involve overproduction of endogenous vitamin D, but the exact mechanism remains unknown (3).
Lead poisoning in infants and children may be diagnosed in screening programs, clinically, or radiographically. Plumbism in children can be traced to pica (eg, dirt eating), acute ingestion of lead-based paints (Fig 3), consumption of home remedies, inhalation of toxic fumes, and rarely, absorption of lead-containing material from metallic or bullet fragments in a serous cavity or joint.
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Figure 3. Anteroposterior abdominal radiograph reveals multiple metallic particles (arrows) confined to the colon in a 22-month-old boy with acute lead ingestion. (Image courtesy of J. P. Cutting, MD, National Naval Medical Center, Bethesda, Md.)
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In general, lead lines indicate past lead exposure and correlate with a blood lead level of 70 µg/dL (3.381 µmol/L)(6); however, in a more recent study (7), dense metaphyseal bands were demonstrated on images obtained in patients with mean blood lead levels of 50 µg/dL (2.415 µmol/L). The sclerosis caused by lead poisoning involves all metaphyses and frequently is associated with remodeling changes and potential undertubulization (3,8). The presence of a dense metaphyseal band at the proximal fibula is a strong indication of plumbism (7), although the mechanism related to the lead toxicity remains unknown.
Because laboratory analysis of lead levels cannot always be readily performed, infants with unexplained encephalopathy should undergo radiography of the knees. The presence of dense metaphyseal bands strongly supports the diagnosis of lead toxicity (9). With treatment or cessation of lead exposure, the lead band will demonstrate an apparent migration into the metadiaphysis because of normal new bone growth. Accordingly, when the lead level returns to normal, the metaphyseal band will gradually decrease in radiopacity and disappear in approximately 4 years.
Lead exposure remains a serious problem in children in the United States (10). With respect to the neurocognitive deficits that result from lead poisoning, the U.S. Centers for Disease Control and Prevention have recently lowered the threshold lead level to 10 µg/dL (0.483 µmol/L). Therefore, knowledge of the radiographic findings of lead poisoning makes the dense metaphyseal band sign increasingly important.
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Footnotes
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The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States government.
A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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Resnick D, Manolagos SC, Fallon MD. Histogenesis, anatomy, and physiology of bone. In: Resnick D, eds. Bone and joint imaging. 2nd ed. Philadelphia, Pa: Saunders, 1996; 2-8.
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Leone AJ. On lead lines. AJR 1968; 103:165-167.[Free Full Text]
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Swischuk L. . Metaphyseal abnormalities. In: Tracy TM, eds. Differential diagnosis in pediatric radiology. Baltimore, Md: Williams & Wilkins, 1984; 226-229.
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Eisenberg R. Skeletal patterns. In: Berk RN, eds. Clinical imaging: an atlas of differential diagnosis. 3rd ed. Philadelphia, Pa: Lippincott-Raven, 1997; 808-811.
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Resnick D. Heavy metal poisoning and deficiency. In: Resnick D, eds. Bone and joint imaging. 2nd ed. Philadelphia, Pa: Saunders, 1996; 912-915.
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Sachs HK. The evolution of the radiologic lead line. Radiology 1981; 139:81-85.[Abstract/Free Full Text]
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Blickman JG, Wilkinson RH, Graef JW. The radiologic "lead band" revisited. AJR 1986; 146:245-247.[Abstract/Free Full Text]
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Pease CN, Newton GG. Metaphyseal dysplasia due to lead poisoning in children. Radiology 1962; 79:233-240.
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Woolf DA, Riach IC, Derweesh A, Vyas H. Lead lines in young infants with acute lead encephalopathy: a reliable diagnostic test. J Trop Pediatr 1990; 36:90-94.[Abstract/Free Full Text]
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Berlin CM. Lead poisoning in children. Curr Opin Pediatr 1997; 9:173-177.[Medline]
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N. S. Rosen and S. A. Raber
Another Cause for Dense Metaphyses Dr Raber responds:
Radiology,
July 1, 2000;
216(1):
306 - 306.
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