evidence that tumours of this nature can and d o occur, although it may be difficult to distinguish between benign and malignant lesions, and their appearance depends on which part of the anatomical peritoneum, mesothelium, or fibrous layer is the site of origin of the tumour. This is, perhaps, best summarized by Thompson (1955) in these words: " T h e present concept of mesotheliomas emphasizes their pleomorphic nature. While formerly pleural, pericardial, and peritoneal mesotheliomas and solitary fibrous and diffuse superficial mesotheliomas were considered as separate entities, the tendency now is more to consider them merely as pleomorphic forms of the same pathological process. T h u s mesotheliomas may be fibroblastic, epithelial, completely undifferentiated, or mixed in type and may involve any serosal surface." Stout (1954), quoted by Ackerman (1954), classifies these benign tumours as (I) Fibrous-local and diffuse; (2) Papillary-local and diffuse. Out of 56 cases of benign peritoneal and pleural tumours over a period of 32 years, only 2 were fibrous and diffuse and they involved the pleura only. Neither author had seen a case involving the peritoneal cavity. Clinically, these tumours are silent unless they produce ascites (Rhind and Wright, 1949), or unless one or more processes undergo torsion as in the case here reported. It is possibly never justifiable to diagnose a benign peritoneal tumour clinically, though
it may be considered i n the differential diagnosis.
T h e true pathological condition more often is revealed by laparotomy for a different lesion or at post-mortem examination.
SUMhWRY
A case of peritoneal fibromatosis presenting as a n acute abdominal emergency is reported. The pathological and clinical significance is considered.
M y thanks are due to Mr. Rose for allowing me to report this case and to Professor Campbell and Dr. Sclare for their report on the histological appearances. I would also like to thank Professor Boyd for his help and advice. REFERENCES ACKERMAN, L. V. (I954), Atlas of Tumor Pathology, Sect. VI, Fasc. 23 and 24, 97. Washington: Armed Forces Institute of Pathology.