Published online before print September 24, 2001, 10.1148/radiol.2212991231
(Radiology. 2001;221:347-348.)
© RSNA, 2001
The Hair-on-End Sign1
Margaret A. Hollar, DO
1 From the Department of Radiology, Division of Neuroradiology, University of Rochester School of Medicine and Dentistry, NY. Received June 28, 1999; revision requested August 16; revision received February 11, 2000; accepted February 28. Address correspondence to the author, Department of Radiology, Montgomery Hospital, 1301 Powell St, PO Box 992, Norristown, PA 19404-0992 (e-mail: dobrain@hotmail.com).
Index terms: Anemia, 11.65 • Signs in Imaging • Skull, abnormalities, 11.65
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APPEARANCE
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The hair-on-end sign is a finding seen in the diploic space on skull radiographs (Fig 1) and has the appearance of long, thin vertical striations that look like hair standing on end. Similar appearances can be seen at magnetic resonance (MR) imaging (Fig 2) and computed tomography (1,2).
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Figure 2. Sagittal T1-weighted (repetition time msec/echo time msec, 500/20) MR image in a 10-year-old boy with sickle cell anemia. There is marked widening of the diploic space containing alternating bands (arrows) of hypointense trabeculae and hyperintense marrow.
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EXPLANATION
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The skull alterations are due to overactivity of the red marrow in response to anemia. This marrow hyperplasia widens the diploic space and thins the outer table. There is trabecular destruction with thickening of the residual trabeculae. The trabecular pattern within the diploë may sometimes be arranged perpendicular to the curvature of the cranial vault. The alternating opaque, thickened trabeculae and radiolucent marrow hyperplasia produce the hair-on-end appearance (3).
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DISCUSSION
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Like the changes in the axial and appendicular skeleton, skull abnormalities in patients with anemia are produced by cellular hyperplasia, circulatory factors, or a combination of both (4). The lesions caused by red marrow hyperplasia, such as expansion of the diploë, thinning of the outer table, and vertical trabeculations (hair-on-end signs), have been described by investigators as being seen in patients with thalassemia major, iron deficiency anemia, sickle cell disease, and spherocytosis (3–5).
The skull changes are more consistently severe in patients with thalassemia major (Fig 1) than in those with any other condition that produces marrow hyperplasia (5). In a study of 60 patients (aged 11–16 years) with thalassemia, Wisetsin (6) observed that five (8.3%) had hair-on-end appearance. Red marrow hyperplasia causes widening of the diploic space, and the outer table thins or is completely obliterated. When the hyperplastic marrow perforates or destroys the outer table, it proliferates under the invisible periosteum, and new bone spicules are laid down perpendicular to the inner table (5).
Bone changes in patients with chronic iron deficiency anemia are usually seen in children and, in the United States, tend to be confined to the skull. These patients exhibit the hair-on-end sign.
Sebes and Diggs (4) reported that among 194 patients (aged 4 months to 55 years) with sickle cell disease, skull radiographs of 10 (5%) revealed vertical striations, termed hair-on-end appearance (Fig 2). This appearance was not seen before the age of 5 years (2). The classic hair-on-end sign was recognized only when thin spicules were observed. There was no correlation between the prominence of this finding and the clinical course of the disease, nor was there a consistency or relationship connecting onset, progression, and severity of the anemia (4).
It is debatable whether the hair-on-end sign may be reversed following treatment of anemia. Moseley (5) reported that resolution of the hair-on-end appearance following treatment begins with the development of a new, compact outer table of the skull. Some radial spicules may remain even after the new outer Table is formed, but eventually the spicules disappear and the size of the diploic space, while still wider than normal, is decreased. However, Sebes and Diggs (4) subsequently reported that the hair-on-end sign persisted without regression in all patients observed from 2
months to 22 years. His group failed to confirm the reversibility of the hair-on-end changes as previously reported by Moseley.
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FOOTNOTES
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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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Murphy KJ. Skull abnormalities on MR of children with sickle cell disease (letter). AJNR Am J Neuroradiol 1997; 18:596.
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Fernandez M, Slovis TL, Whitten-Shurney W. Maxillary sinus marrow hyperplasia in sickle cell anemia. Pediatr Radiol 1995; 25:209-211.
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Williams AO, Lagundoye SB, Johnson CL. Lamellation of the diploe in the skulls of patients with sickle cell anaemia. Arch Dis Child 1975; 50:948-952.
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Sebes JI, Diggs LW. Radiographic changes of the skull in sickle cell anemia. AJR Am J Roentgenol 1979; 132:373-377.
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Moseley JE. Skeletal changes in the anemias. Semin Roentgenol 1974; 3:169-183.
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Wisetsin S. Cephalography in thalassemic patients. J Dent Assoc Thai 1990; 40:260-268.
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B. M. Rothschild and M. A. Hollar
Hair Standing on End as a Manifestation of Iron Deficiency? * Dr Hollar responds:
Radiology,
August 1, 2002;
224(2):
609 - 610.
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