Correspondence Amis, 1991). Typically IRF appears on CT as a well-defined periaortic retroperitoneal soft tissue mass (Brooks et al, 1987). However, this appearance can be similar to that found in malignant retroperitoneal fibrosis (Brooks et al, 1987). Atypical cases of IRF are not infrequent. Thefibroticmass can grow in the peripancreatic or periduodenal regions or present as an isolated mass in a paravertebral or mesenteric location (Inaraja et al, 1986; Brooks, 1990; Amis, 1991). Mesenteric lymphadenapathy can represent another unusual manifestation of IRF which, to our knowledge, has not been reported previously. Yours etc., F. POMBO J. PEREZ-FONTAN E. RODRIGUEZ

Department of Radiology, Hospital Juan Canalejo, Xubias de Arriba, 84, 15006 La Coruna, Spain {Received 3 March 1992, accepted 10 April 1992) References AMIS, E. J., 1991. Retroperitoneal fibrosis. American Journal of Roentgenology, 157, 321-329. BROOKS, A. P., 1990. Computed tomography of idiopathic retroperitoneal fibrosis ("periaortitis"): variants, variations, patterns and pitfalls. Clinical Radiology, 42, 75-79. BROOKS, A. P., REZNEK, R. H., WEBB, J. A. W. & BAKER, L. R. I.,

1987. Computed tomography in the follow-up of retroperitoneal fibrosis. Clinical Radiology, 38, 597-601. INARAJA, L., FRANQUET, T., CABALLERO, P., ENCABO, B. & HUM-

BERT, P., 1986. CT findings in circumscribed upper abdominal idiopathic retroperitoneal fibrosis: case report. Journal of Computer Assisted Tomography, 10, 1063-1064. MITCHINSON, M. J., 1984. Chronic peri-aortitis and peri-arteritis. Histopathology, 8, 589-600.

Now you see it...now you don't THE EDITOR—SIR,

We were interested to read the case report by J. S. Millar (1992) showing the unusual appearance of a para-umbilical hernia. In the discussion the author states that the diagnosis of a diaphragmatic hernia is usually obvious. McHugh et al (1991) makes the point that plain radiographic findings of diaphragmatic hernia are often nonspecific and that when suspected a contrast study should be performed. We present a case in which the diaphragm could not be seen but in which the presence of a stricture suggested the correct diagnosis. A 78-year-old lady was referred with constipation, abdominal pain and distention. A chest radiograph showed a left pleural effusion and free gas under the right hemidiaphragm. The supine abdominal radiograph revealed distention of both large and small intestine. A gastrografin enema (Fig. 1) demonstrates a short extrinsic stricture in the region of the splenic flexure and a healedribfracture (from an accident 20 years previously). A diagnosis of incarcerated diaphragmatic hernia was suspected and confirmed at laparotomy.

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Figure 1. Spot view from the gastrografin enema. Open arrows mark the short extrinsic stricture in the splenic flexure. Closed arrow indicates the healed rib fracture of the left 9thrib.The diaphragm cannot be seen.

The free air was due to caecal perforation. 90% of traumatic herias of the diaphragm are left sided, they usually result from blunt abdominal injury. Approximately one third of cases will have a delayed presentation. The diagnosis is straight forward if there is an appropriate history and the combination of an elevated hemidiaphragm and high splenic flexure or, if bowel loops are visible in the chest. In fact this is not often the case. A spectrum of radiological appearance exists, changes are often minimal. Even a large diaphragmatic defect may be difficult to recognize with herniated bowel mimicking diaphragmatic contour. Pleural effusion or basal shadowing are frequently present but, if the diaphragm is obscured, may mask the true diagnosis. Yours etc., D. KESSEL *P.E. BEARN

Departments of Radiology and *Surgery, Middlesex Hospital, Mortimer Street, London WIN 8AA (Received 9 March 1991, accepted 15 April 1992) References MCHUGH K., OGILVIE, B. C. & BRUNTON, F. J., 1991. Delayed pres-

entation of traumatic diaphragmatic hernia. Clinical Radiology, 43, 246-250. MILLAR, J. S., 1992. Now you see it... now you don't. British Journal of Radiology, 65, 183-184.

The British Journal of Radiology, June 1992