Benign hamartoma of the liver.

Sheehan (1930) when describing a malignant liver tumour in a young child, first brought together a number of such tumours previously described under a variety of names, such as 'sarcoma', 'endothelioma' or 'angeiosarcoma', and pointed out that they were probably all derived from rests of undifferentiated mesenchymal cells and were in fact embryonic growths. The tumour he described consisted largely of undifferentiated mesenchyme forming cysts lined with bile-duct epithelium, but in one cyst the basic cells showed malignant features with vascular invasion. In other places they had differentiated into myxoma, fibrous tissue, acinar tissue and striated muscle. These tumours are evidently rare and few later reports are available (e.g., Nissel, 1928; Roth, 1938; Webster, 1938; Wells, 1940; McRae, 1935). All appear to accept an embryonic origin for the tumours and, indeed, Roth termed his a 'unilayered teratoma'. All the tumours so far reported appear to have been malignant with multiple vascular metastases within