Doughnut lesions in the brain, originally described on radioisotope brain scans, are now more familiar from their computerized tomography and magnetic resonance imaging appearances. ‘Soon after the introduction of rectilinear scintillation scanning in 1955, focal organic lesions of the brain were delineated following the administration of various gamma-emitting compounds. Classically, these lesions have been identified as a locus of increased radioactivity within the low activity of normal brain tissue … Since 1964, the use of large doses of short-lived agents, such as 99m Tc pertech-netate, has resulted in a better delineation of these lesions.’ 1 This newer technology allowed Robert O’Mara and his colleagues’, from the State University of New York in Syracuse, to note a pattern that differed from the classical one, i.e. a zone of increased uptake containing a central core of decreased activity—the doughnut sign (Figures 1 and 2). They studied more than 1400 scans in 18 months to determine the incidence and diagnostic significance of this sign. They credit Alexander Gottschalk and co-workers 2 for reporting a similar pattern. Their conclusion was that it ‘is a relatively uncommon appearance since the pattern was observed in only 2.9 per cent of all positive studies [and was] of little value in indicating the etiology of a lesion.’ 1 The doughnut sign had been seen in metastases, primary tumors, abscesses, hematomas and with cerebrovascular accidents. This still constitutes a significant list of differential diagnostic possibilities. ‘The doughnut sign … usually, though not invariably, indicates central necrosis, hemorrhage, or cyst formation within a lesion … it may be helpful to the neurosurgeon to be forewarned that a lesion is likely to contain central necrosis or hemorrhage.’ 1 ‘Anterior scan demonstrates a large area of increased radioactivity surrounding a central area of decreased activity. This is consistent with the ‘doughnut sign’ of central necrosis.’ Reprinted from O’Mara et a/.’ The doughnut sign in cerebral radioisotopic images. <italic>Radiology,</italic> 1969, 92, 581 <italic>-6,</italic> with permission of the RSNA https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003076568/34c29fd5-5662-4e8f-b58c-badd7fa5d724/content/fig28_1_B.jpg"/> Computerized tomograph of the head of a patient with bleeding aneurysm showing doughnut pattern with hyperdense periphery and central area of decreased attenuation. Case courtesy of Dr M. Rothman. University of Maryland https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003076568/34c29fd5-5662-4e8f-b58c-badd7fa5d724/content/fig28_2_B.jpg"/>