(Radiology. 2000;215:884-885.)
© RSNA, 2000
The Panda Sign1
Karen A. Kurdziel, MD
1 From the Imaging Sciences Training Program, National Institutes of Health, Bldg 10, Rm 1C401, MSC 1C497, Bethesda, MD 20892. Received July 14, 1998; revision requested August 13; final revision received March 18, 1999; accepted April 8. Address correspondence to the author (e-mail: kurdziel@nmdpet.cc.nih.gov).
Index terms: Lacrimal gland and duct, 223.12161, 223.22 • Nasopharynx, 263.12161, 263.22 • Parotid gland, radionuclide studies, 2641.12161, 2641.12176, 2641.22 • Salivary glands, radionuclide studies, 264.12161, 264.12176, 264.22 • Sarcoidosis, 223.22, 263.22, 2641.22 • Signs in Imaging
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APPEARANCE
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Focal accumulation of gallium 67 citrate in the nasopharynx, parotid gland, and lacrimal gland produces a distinctive pattern, the panda sign, that is strikingly similar to the dark markings of the giant panda. It is seen at anterior planar 67Ga citrate scintigraphy of the head (Fig 1).
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Figure 1. 67Ga citrate planar image shows the panda sign in a patient with sarcoidosis. Note the normal nasopharyngeal uptake (arrowhead). Bilateral radionuclide uptake is seen in the lacrimal (straight arrow) and parotid (curved arrow) glands. (Image courtesy of Stephanie Spottswood, MD, Department of Radiology, Medical College of Virginia of Virginia Commonwealth University, Richmond.)
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EXPLANATION
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The panda sign is produced as a result of 67Ga citrate accumulation in both regions of chronic and regions of acute inflammation, as well as in some malignancies (eg, lymphoma, bronchogenic carcinoma, and melanoma), although the exact mechanism of 67Ga citrate localization is incompletely defined (1). When the normal accumulation of the radionuclide in the nasopharynx is combined with increased symmetric accumulation in the parotid and lacrimal glands, the image shows a striking similarity to the mottled coloring of the giant panda (Fig 2).
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Figure 2. Photograph of a giant panda. The panda's black nose correlates with the normal nasopharyngeal uptake; the black fur around the eyes (straight arrow), with the intense lacrimal uptake; and the gray blush on the cheeks (curved arrow), with the abnormal parotid uptake. (Reprinted, with permission, from reference 2.)
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DISCUSSION
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The panda sign has been classically described as indicating sarcoidosis, a relatively common, chronic, systemic, granulomatous disease. In the United States, the prevalence of sarcoidosis ranges from 10 to 40 per 100,000 persons (higher in the Southeast and in blacks), with a slight predominance in women (3). Bilateral inflammatory involvement of the parotid and lacrimal glands results in 67Ga citrate uptake and production of the panda sign. The presence of perihilar adenopathy adds the 
distribution of increased uptake in the chest, which at times has been included in the description of the panda distribution (4–6). In one study (5), 79% (51 of 65) of patients with sarcoidosis exhibited the panda pattern. When correlated with the sarcoidosis stage, the panda sign showed an 80% (20 of 25) sensitivity for stage I and a 74% (17 of 23) sensitivity for stage II disease, with 74% (48 of 65) of patients with stage I or II sarcoidosis at presentation.
This pattern is not specific for sarcoidosis, although it is one of few disorders that affect the salivary and lacrimal glands symmetrically. The panda sign was seen in 4% (23 of 540) of patients who did not have sarcoidosis (5). Since 67Ga citrate accumulates in areas of inflammation and malignancy, the differential diagnosis for the symmetric bilateral accumulation in the lacrimal and salivary glands includes lymphoma (after irradiation), Sjögren syndrome, and acquired immunodeficiency syndrome (4,5). The panda sign is seen less frequently in these entities, since bilateral symmetric involvement is not common.
In summary, symmetric uptake of 67Ga citrate in the face is most often associated with inflammatory response in sarcoidosis and is most prominent in stage I or II disease (4,5). Although the panda sign is not specific for sarcoidosis, recognition of it limits the differential diagnosis. Other clinical conditions that exhibit the panda sign can usually be separated on a clinical or radiographic basis.
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Acknowledgments
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Special thanks to Melvin J. Fratkin, MD, and Paul R. Jolles, MD, for their support and review of the manuscript.
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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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Hoffer P. Gallium: mechanisms. J Nucl Med 1980; 21:282-285.[Free Full Text]
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CyberPanda home page; Available at: http://www.cyberpanda.com. Accessed May 19, 1999..
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Crystal RG. Sarcoidosis. In: Isselbacher AB, Braunwald E, Wilson JD, Martin JB, Fauci AS, Kasper DL, eds. Harrison's principles of internal medicine (book on CD-ROM). 13th ed. New York, NY: McGraw-Hill, 1994.
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Mana J. Nuclear imaging: 67gallium, 201thallium, 18F-labeled fluoro-2-deoxy-D-glucose positron emission tomography. Clin Chest Med 1997; 18:799-811.[Medline]
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Sulavik SB, Spencer RP, Weed DA, Shapiro HR, Shiue ST, Castriotta RJ. Recognition of distinctive patterns of gallium-67 distribution in sarcoidosis. J Nucl Med 1990; 31:1909-1914.[Abstract/Free Full Text]
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Oates EM, Metherall J. Sarcoidosis. N Engl J Med 1993; 329:1394.[Free Full Text]
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