Doughnut sign

Fig. 1.48a,b. The crescent-in-doughnut sign. Axial US scans obtained at the middle (apex proximal regions) (a) and at the base (b) of an intussusception, show the central limb of the intussusceptum (C) eccentrically surrounded by the hyperechoic mesentery (M), a situation that produces the crescent-in-doughnut sign [From del Pozo (1999)]... 

Whilst the sonographic appearances of an intussusception are straightforward, care must still be taken not to confuse these appearances with other causes of bowel wall thickening such as inflammation, oedema, haematoma or any area of volvulus. Nevertheless these other conditions will not show the characteristic crescent and doughnut sign. 

The shape of the 2p orbital can be deduced from equation (6.29). The presence of the Cartesian coordinate jc in the expression for 2p means that there will be a node in the wavefunction in the yz plane. The surface of constant jf is illustrated in Figure 6.10. The full three-dimensional orbital shape can be obtained by rotating the profile about the x axis. It is seen to consist of two doughnut-shaped lobes of opposite sign. The 2p orbital will be similar, but oriented along the y axis. 

Swischuk LE, Hayden CK, Boulden T (1985) Intussusception indications for ultrasonography and an explanation of the doughnut and pseudokidney signs. Pediatr Radiol 15 388-391... 

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