Is this a kidney or a spleen?

Question 13.2 from the first paper of 2008 asked the candidates to list the features of a palpable left upper quadrant mass which might help you decide whether it is a kidney or a spleen. It is almost a shame to dedicate an entire chapter to the kidney-spleen controversy. In brief, the differences between spleens and kidneys are mobility, ballotability, and edge palpation.

Of course, if something is worth doing, its worth over-doing. In that spirit, Let us talk about the palpation of the spleen. The most detailed review of this issue is a 1991 article by Barkun et al, "The bedside assessment of splenic enlargement."  A good overview is also offered in Chapter 150 ("Spleen") by James O. Armitage, from the 3rd edition of Clinical Methods: The History, Physical, and Laboratory Examinations.

• The spleen is mobile with respiration, whereas the kidneys is not.
• The kidney is "ballotable" whereas the spleen is not.
• The spleen has a notch on the anterior surface, and the kidney does not
• The spleen should be dull to percussion, where the kidney can be resonant due to overlying gas.
• Traube's space percussion: the sixth rib superiorly, the midaxillary line laterally, and the left costal margin inferiorly. This area should be dull on expiration.
• Middleton's manoeuvre:  The patient is asked to lie flat with his or her left fist under their back, at the left costovertebral angle. The examiner is positioned to the patient's left, facing the patient's feet. The fingers of both the examiner's hands are curled under the left costal margin, and the patient is asked to take a long, deep breath as the palpation of a descending spleen is sought.
• The spleen enlarges diagonally, towards the umbilicus and the RLQ, whereas the kidney enlarges inferiorly, to the ipsilateral pelvis.
• There is no palpable upper border to the spleen, whereas the kidney should have one
• There is a splenic rub on auscultation (whereas the kidney does not rub).