DOI: 10.1148/radiol.2463050903
(Radiology 2008;246:980-981.)
© RSNA, 2008
The Polka-Dot Sign1
Thara Persaud, MB
1 From the Department of Radiology, the Adelaide and Meath Hospital, Tallaght, Dublin 24, Ireland. Received May 31, 2005; revision requested July 21; revision received September 2; final version accepted November 8.
Address correspondence to the author (e-mail: tpersaud4{at}hotmail.com).
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APPEARANCE
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The polka-dot sign is seen on transverse computed tomographic (CT) images of vertebral bodies. The medullary cavity of the vertebral body shows numerous high attenuation dots (Figure), simulating the polka-dot pattern on clothing.
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EXPLANATION
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The polka-dot sign on CT images is produced by thickened trabeculae in a vertebral body hemangioma, seen in cross section as small punctate areas of high attenuation. The trabecular thickening occurs due to reinforcement of the osseous network adjacent to the vascular channels of the lesion that have caused bone resorption (1,2). This process occurs within the fatty marrow.
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DISCUSSION
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Osseous hemangiomas are benign lesions characterized by vascular spaces lined with endothelial cells. They are common in the spine and calvaria and less frequently affect long bones such as the tibia, femur, and humerus. Vertebral hemangiomas account for 28% of all skeletal hemangiomas, with the thoracic spine being the most common location (1). Hemangiomas are usually asymptomatic and are often an incidental finding. One large study of autopsies (3) found a frequency of 11% for vertebral hemangiomas. However, with modern imaging, many small hemangiomas are now detected, and it is likely that the frequency is substantially higher than the quoted 11%. Men are affected twice as often as women, and lesions are usually discovered in the 4th–5th decade of life (1). These lesions can involve a portion or the entirety of the vertebral body, and they are multiple in one-third of patients (4).
Most vertebral hemangiomas are asymptomatic and are of no clinical importance; however, occasionally neurologic symptoms from vertebral collapse or extension into the spinal canal causing compression may result in pain and/or paraplegia, particularly if the lesion extends into the posterior elements or surrounding soft tissue (2,4). Vertebral hemangiomas demonstrate regular vertical striations and a normal cortex on conventional spinal radiographs. There is usually incomplete involvement of the vertebral body. The neural arch and surrounding soft tissue typically are normal (5).
Vertebral hemangiomas are composed of a stroma within an osseous network. Laredo et al (2) studied the CT attenuation values of the stroma as an indication of lesion characterization and behavioral pattern. They found the stroma could have fat or soft-tissue attenuation or both. Asymptomatic vertebral hemangiomas tended to have a more fatty content, as shown by negative attenuation values on the CT scan, while those with more vessels and higher attenuation were more likely to be symptomatic.
At magnetic resonance imaging, vertebral hemangiomas typically have high signal intensity on both T1- and T2-weighted images. The extent of high signal intensity is, however, variable, depending on the degree of fat present. The larger the degree of fatty material in the stroma between thickened trabeculae, the higher the signal intensity.
The polka-dot appearance on CT images is representative of a benign hemangioma. In the literature, the differential diagnosis for an osseous hemangioma based on radiographic findings has been described by Liu et al (6). They reported on a skull base hemangioma that demonstrated the classic radiologic features. The possible diagnoses included chondrosarcoma and intraosseous meningioma. Bemporad et al (7) reported an unusual radiologic manifestation of a primary Ewing sarcoma of the cervical spine. At CT, a coarse trabecular pattern was demonstrated. This was accompanied by a dumbbell-shaped epidural soft-tissue mass seen extending out of the neural foramen, with associated cord compression. Intraosseous hemangiomas need to be differentiated from sarcomas; the latter commonly show aggressive characteristics such as destruction of the bone cortex and invasion of the periosteum.
In summary, the polka-dot sign on transverse CT images of a vertebral body is produced by thickened trabeculae in a vertebral body hemangioma.
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ACKNOWLEDGMENTS
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I am grateful to William C. Torreggiani, MB, for his invaluable guidance and support in the preparation of this article.
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FOOTNOTES
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Author stated no financial relationship to disclose.
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References
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- Murphey MD, Fairbairn KJ, Parman LM, Baxter KG, Parsa MB, Smith WS. Musculoskeletal angiomatous lesions: radiologic-pathologic correlation. RadioGraphics 1995;15:893–915.[Abstract]
- Laredo JD, Assouline E, Gelbert F, Wybier M, Merland JJ, Tubiana JM. Vertebral hemangiomas: fat content as a sign of aggressiveness. Radiology 1990;177:467–472.[Abstract/Free Full Text]
- Huvos AG. Hemangioma, lymphangioma, angiomatosis/lymphangiomatosis, glomus tumor. In: Bone tumors: diagnosis, treatment, and prognosis. 2nd ed. Philadelphia, Pa: Saunders, 1991; 553–578.
- Karlin CA, Brower AC. Multiple primary hemangiomas of bone. AJR Am J Roentgenol 1977;129:162–164.[Medline]
- Laredo JD, Reizine D, Bard M, Merland JJ. Vertebral hemangiomas: radiologic evaluation. Radiology 1986;161:183–189.[Abstract/Free Full Text]
- Liu JK, Burger PC, Harnsberger HR, Couldwell WT. Primary intraosseous skull base cavernous hemangioma: case report. Skull Base 2003;13(4):219–228.[CrossRef][Medline]
- Bemporad JA, Sze G, Chaloupka JC, Duncan C. Pseudohemangioma of the vertebrae: an unusual radiographic manifestation of primary Ewing's sarcoma. AJNR Am J Neuroradiol 1999;20(10):1809–1813.[Abstract/Free Full Text]
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