In 1890, in the first volume of Archives of Surgery, Hutchinson commented that, in elderly patients, arteries are liable to a spreading inflammation which glues the artery to its sheath. He noted that inflammation was the hallmark of atheroma, differentiating it from senile change or fatty degeneration.

Chronic inflammation in the aortic adventitia is commonly seen in association with advanced atherosclerosis when the aortic media is thinned (Fig. 1) 204. This condition is known as chronic periaortitis. Chronic periaortitis is most common, and most severe, at sites where atherosclerosis is also most severe (see Section 7.1) 33, notably in the lower abdominal aorta.

The inflammatory cells consist of lymphocytes and plasma cells (Fig. 2) 205. The degree of inflammation varies: it is usually minimal, or subclinical, and is only noted on histological examination. Occasionally, the inflammation is severe enough to be visible macroscopically or on computed tomography (CT) scan. At this stage it is likely to produce clinical effects. Clinical chronic periaortitis can be seen in dilated or undilated aortas.

‘Idiopathic retroperitoneal fibrosis’ was first described by Albarran in 1905 but is best known by the name of Ormond who described it in 1948. It is typically a disease of middle-aged to elderly males who develop chronic inflammation and fibrosis around the lower abdominal aorta (see Section 7.1) 33. This inflammatory process tends to drag neighbouring hollow structures towards the midline. The disease usually presents as a urological problem with obstruction of one or both ureters, often resulting in hydronephrosis.

The periaortic distribution of the idiopathic retroperitoneal fibrosin first emerged from necropsy studies (Fig. 3) 206 and has been confirmed by CT (Fig. 4) 207. The presentation is associated with a raised erythrocyte sedimentation rate and there is often a dramatic response to steroids. Histopathological examination reveals advanced aortic atherosclerosis with medial disruption and adventitial infiltrates of lymphocytes and plasma cells. The degree of atherosclerosis is not always appreciated as the fibrous tissue alone is often submitted for histological examination following surgical mobilization of the ureters.

A similar chronic inflammatory process around the thoracic aorta occurs much less commonly. This is known as idiopathic mediastinal fibrosis. The histopathological findings in these two conditions are identical, and they may occur in contiguity through the diaphragm.

Retroperitoneal fibrosis has been associated with the use of methysergide, an indole derivative with a strong structural similarity to serotonin which is used in the treatment of migraine. Its mechanism of action is uncertain but in the index of idiopathic retroperitoneal fibrosis it is suggested that the vessel wall is damaged by vasospasm provoked by the drug simulating the peripheral effects of serotonin. Idiopathic retroperitoneal fibrosis in patients treated with methysergide is often accompanied by fibrosis at other sites.

The rapidity with which patients with ureteric obstruction respond to corticosteroid treatment supports the view that the ureter is not blocked by fibrosis but rather by oedema and inflammation. This is confirmed histologically, although it is not known whether this oedema and inflammation obstructs the ureter directly or indirectly, by interfering with nerves or blood supply. Despite the value of steroid therapy, almost all surgeons still regard ureterolysis as the first line of management.

The term idiopathic retroperitoneal fibrosis is misleading: the disease is not idiopathic, but secondary to atherosclerosis; it is not retroperitoneal, but periaortic. The term is also misleading because it allows the incorporation of eccentric causes of fibrosis in the retroperitoneum, such as malignant neoplasm, endometriosis and diverticulitis (Table 1) 169 into the category of what is a periaortic disease.

Occasionally, the surgeon sees an abdominal aortic aneurysm encased in fibrous tissue that extends into the retroperitoneum (Figs. 5 and 6) 208,209. These so-called ‘inflammatory aneurysms’ of the aorta have a reported incidence of 2.5 to 10 per cent of all aortic aneurysms.

Inflammation of the aorta (‘aortitis’) has been recognized as an entity since the late sixteenth century when aortic aneurysm was known to be associated with syphilis. From the fifteenth century until the beginning of this century, syphilis was widespread in many countries and was probably the most common cause of aortitis. Today, there are numerous rare causes of aortitis which can lead to aneurysm formation (Table 2) 170.

Abdominal aortic aneurysms are most commonly associated with advanced atherosclerosis. The aneurysm is secondary to thinning of the aortic media, probably due to the atherosclerosis. For some time, surgeons and pathologists have tended to classify these abdominal aortic aneurysms as either ‘atherosclerotic’ or ‘inflammatory’. Recent large reviews from the Mayo Clinic in the United States and from Cambridge and Oxford in the United Kingdom have confirmed that all atherosclerotic abdominal aortic aneurysms are inflamed, but to a varying degree. The factors that determine the degree of chronic inflammation associated with atherosclerosis at this site remain unknown.

To add to the confusion, the term perianeurysmal retroperitoneal fibrosis has been used to describe the condition in which ureteric blockage has occurred as a result of fibrosis around atherosclerotic aneurysms of the abdominal aorta. The inflammatory infiltrate is the same as that seen in both idiopathic retroperitoneal fibrosis and inflammatory aneurysms, there is a raised erythrocyte sedimentation rate, and the disease responds to treatment with corticosteroids. Ureteral disease may occur in up to 23 per cent of patients with inflammatory aneurysms. The term inflammatory aneurysm is, therefore, misleading, since it perpetuates the image of aneurysm secondary to an inflammatory process. While this may be the mechanism underlying mycotic aneurysm, which is very rare, both medial thinning, giving rise to aneurysmal dilatation, and adventitial inflammation are sequelae of atherosclerosis (see Section 7.1) 33.

Inflammation and fibrosis are frequently seen around coronary arteries in association with advanced atherosclerotic plaques. In this situation, the triad of atherosclerosis, medial thinning, and adventitial inflammation is termed chronic periarteritis.

The unifying concept of chronic periaortitis as a local complication of atherosclerosis brings together the conditions previously termed idiopathic retroperitoneal fibrosis, inflammatory aneurysm, and perianeurysmal retroperitoneal fibrosis as part of a spectrum of the same disease, having in common advanced atherosclerosis, medial thinning, and adventitial chronic inflammation.

The histopathological findings—including characterization of the inflammatory cell populations (Fig. 7) 210, clinical presentation and CT appearances of idiopathic retroperitoneal fibrosis, and inflammatory aneurysms show no important differences except that in the latter, the aortic diameter is increased. The factors which determine why some atherosclerotic aortas dilate and others do not are unknown, but hereditary defects in aortic collagen and elastin may play a role (see Section 7.1) 33.

Inflammation is more likely to be a consequence of the atheroma than a cause, since inflammation is not seen in the adventitia of normal arteries and aortas, or in atherosclerotic plaques. In these cases, the media is intact. Immunoglobulin-secreting plasma cells occur in the aortic adventitial infiltrate in chronic periaortitis; this has been interpreted as evidence that chronic periaortitis is due to an autoimmune reaction to a component of the atherosclerotic plaque, likely to be a component of oxidized lipid or ceroid (see Section 7.1) 33. Immunoglobulin, predominantly IgG, is associated with ceroid in plaques in patients with severe chronic periaortitis. Furthermore, antibodies to oxidized low-density lipoprotein and ceroid are detectable in patients with severe chronic periaortitis.

Computed tomography (CT) has an established role in the preoperative diagnosis of chronic periaortitis, by demonstrating the periaortic mass. Shrinkage of the periaortic mass does occur in response to steroid therapy of idiopathic retroperitoneal fibrosis. The mass in chronic periaortitis probably shrinks as part of its natural history. The variable proportion of cells and fibrous tissue seen histologically in chronic periaortitis suggests that in its early stages the tissue is highly cellular and contains immature fibroblasts; later it evolves into predominantly fibrous tissue, contracting as it does so. Contraction would account for the ‘dragging’ of mobile structures, such as the ureters, medially towards the aorta.

Finally, the core of textbook chronic periaortitis, or rather idiopathic retroperitoneal fibrosis and inflammatory aneurysm, is surrounded by a substantial and mysterious fringe of clinical associations which are ill-defined and which vary in both their severity and characteristics, examples being pulmonary hyalinizing granuloma, lymphomatoid granulomatosis, Reidel's thyroiditis, and sclerosing cholangitis. Studies of idiopathic retroperitoneal fibroses and inflammatory aneurysms have not confirmed these associations.

Albarran J. Rétention renale par periureterité; liberation externe de lúretere. Assoc France Urol, 1905; 9: 511–7.

Baker LRI, et al. Idiopathic retroperitoneal fibrosis; a retrospective analysis of sixty cases. J. Urol, 1988; 60: 497–503.

Hutchinson J. On the diseases of the arteries. Arch Surg 1890; 1: 84–6.

Mitchinson MJ. Chronic periaortitis and periarteritis. Histopathology, 1984; 8: 589–600.

Ormond JK. Bilateral ureteral obstruction due to envelopment and compression by an inflammatory retroperitoneal process. J Urol, 1948; 59: 1072–9.

Parums DV. The spectrum of chronic periaortitis. Histopathology, 1990; 16: 423–31.

Pennell RC. et al. Inflammatory abdominal aortic aneurysms: a thirty year review. J Vasc Surg, 1985; 2: 859–69.