Pseudotumour of the Orbit: a Clinical and Pathological Study of 47 Cases.

ORBITAL pseudotumour is a term used to describe diverse clinical conditions which initially may simulate true orbital tumours but subsequently pursue a benign course. Although the first case was described over a century ago, a survey of the literature reveals little progress in the understanding of the processes involved in the production of pseudotumours. Many ofthe lesions are described as chronic orbital granulomata, but this non-committal term does little to elucidate their origin. Birch-Hirschfeld (1930) was puzzled to find granulomata in sections from orbital material removed from patients free from tuberculosis, syphilis, fungus, or parasitic disease. More recently, Benedict (1949) reported two cases, confirmed histologically, of "solitary orbital sarcoid", but the patients gave no evidence of sarcoidosis or other pathology when traced for 22 years. For these orbital lesions in cases in which granulomatous disease is absent elsewhere' and does not manifest itself later, the name orbital lipogranuloma is here proposed; the present study suggests that these granulomata are due to fat necrosis and its sequelae: the reasons for this opinion are detailed later. Although Reese (1951) noted the presence of fat necrosis in orbital pseudotumours, he regarded it as incidental to inflammation already present. The illustrations in his textbook, however, show features of late stages. Elsewhere in the literature no reference to the role of fat necrosis as an explanation for granulomatous orbital pseudotumours has been found. The present study confirms that even to-day the aetiology remains clinically obscure in many cases, though pathological examinations reveal the cause in some, and clinical follow-up enables a few others to be diagnosed. Confirmation of diagnosis is difficult as the clinical features can be mimicked by many conditions so that the differential diagnosis covers a wide field. This was well demonstrated by Cowan (1951); five clinical diagnoses were made before biopsy and exenteration finally revealed a chronic inflammatory retrobulbar mass. Treatment of the lesion can be rational