Splenomegaly, sometimes of massive extent, occurs in a large number of hereditary diseases, some relatively prevalent and others, rare to ultra-rare. Because physicians are often unfamiliar with the less common disorders, patients may suffer because of diagnostic delay or diagnostic error and may undergo invasive, non-innocuous procedures such as splenectomy that are potentially avoidable were the correct diagnosis suspected. In this review article, we discuss the definition and clinical

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... ations of "massive" splenomegaly and describe several rare genetic disorders that are sometimes associated with marked splenic enlargement as well as four additional hereditary "splenomegalic" lysosomal storage diseases (cholesterol esterase storage disease, Niemann-Pick C disease, acid sphingomyelinase deficiency disease, Gaucher disease) in which approved or promising experimental treatments should generally obviate the need for palliative splenectomy. We also summarize current concepts about the appropriate use of splenectomy in patients with β-thalassemia, hereditary spherocytosis and Gaucher disease and discuss surgical alternatives to classical total splenectomy for these disorders. Based on weight measurements and calculation of volume by water displacement of cadaveric and surgically resected spleens, normal splenic volume in mL in children and adults of all ethnicities and "racial" backgrounds is generally assumed to be 0.2% of total body weight in kilograms (approximately 200 ± 50 mL in an adult 70 kg man) [1] . The normal splenic volume in vivo