Clinical History
An 86-year-old male patient with a history of arterial hypertension, end-stage kidney disease (under dialysis) and an endovascular aneurysm repair (EVAR) 3 years ago, presented to the emergency department with severe anaemia (Hgb 6, 1 g/dL).
Imaging Findings
The abdominal ultrasound (Fig. 1) shows an aneurysmal dilation extending from the infra-renal aorta to the proximal common iliac arteries, with the endovascular prothesis depicted inside. There is diffuse calcification of the native aorta wall. A homogeneously hypoechoic band with irregular margins is seen enfolding the aorta, along the extension of the aneurysm.
A multiphase CT was performed (Fig. 2), which showed preserved permeability of the EVAR and no signs of endoleak. A homogeneous and well-defined mass with irregular borders was identified, wrapping the anterior and lateral portions of the infra-renal aorta and iliac arteries and exhibiting a spontaneous attenuation similar to the paraspinal muscles. This soft-tissue mass appears infiltrative, enveloping the inferior vena cava (IVC), ureters and small arterial vessels without deviating or invading them. The dynamic study demonstrated a mild, homogeneous and progressive enhancement that peaks in the late phase.
Discussion
Idiopathic retroperitoneal fibrosis (RPF or Ormond's disease) is a rare entity characterized by the proliferation of aberrant fibroinflammatory tissue in the retroperitoneum [1].
Clinically, it presents with nonspecific signs and symptoms such as poor-localized abdominal or back pain, anorexia and low-grade fever. When the ureters are involved (more than 56% of the cases) the clinical findings range from acute obstructive uropathy to chronic kidney disease [1, 2].
On ultrasound, it presents as a well-defined hypoechoic or isoechoic band anterior to the aorta, IVC and iliac vessels. As ultrasonography has poor overall sensitivity for RPF, retroperitoneal haematomas, lymphadenopathy or solid neoplasms are a common misdiagnosis [1, 2].
CT is the pillar of noninvasive diagnosis of RPF, as it allows evaluation of RPF location, extent and effect on adjacent organs and vascular structures. The typical findings are a well-delimited but irregular soft-tissue mass that is isodense to the surrounding muscles and extends from infra-renal aorta to the iliac vessels, wrapping the great vessels but sparing their posterior aspect. The centre of the mass is generally at the level of the aortic bifurcation and it often envelops the IVC and the ureters (causing medial deviation of the latter). The degree of soft tissue enhancement after contrast administration correlates with the activity of the fibrotic process [1, 2].
Although CT demonstrates high sensitivity, it lacks specificity to confidently differentiate between idiopathic RPF and the differential diagnosis, namely secondary RPF (mainly caused by malignancy, drugs or infection), lymphoma and retroperitoneal sarcomas. The findings that should prompt suspicion for a non-idiopathic aetiology are peripheral lobulation or nodularity, eccentric location (not centred on the aorta), heterogeneous texture and enhancement, mass effect on neighbouring structures (e.g. anterior dislocation of the great vessels or lateral deviation of the ureters) and the presence of lymphadenopathies [1, 2].
Lymphomas normally have a more cephalad distribution. A perirenal or paraspinal location suggests Erdheim-Chester disease or extramedullary haematopoiesis, respectively [1, 2, 3].
Histopathological confirmation is needed whenever there is clinical suspicion for underlying malignancy, atypical imaging features or progression of the mass [1].
Treatment is normally aimed to relieve ureteral obstruction and is based on corticosteroids or immunossupressive drugs, with surgery reserved for refractory cases [1].
On our case, as there were no symptoms and the patient was already on dialysis, no treatment was performed. The presumptive diagnosis of idiopathic RPF was made based on the absence of atypical imaging features and clinical suspicion of other aetiologies as well as the stability shown on follow-up examinations.
Differential Diagnosis List
Idiopathic retroperitoneal fibrosis
Secondary retroperitoneal fibrosis
Lymphoma
Retroperitoneal sarcoma
Erdheim-Chester disease
Extramedullary haematopoiesis
Final Diagnosis
Idiopathic retroperitoneal fibrosis
