Angiomyolipoma of the kidney: The most frequent cause of atraumatic renal bleeding

Clinical History

A 69-year-old woman was admitted to the emergency department with right flank pain and no history of trauma. Past medical history was unremarkable. Laboratory demonstrated significant anaemia (Hb: 9, 7 g/dl).

Imaging Findings

Contrast-enhanced CT showed a perirenal and retroperitoneal haematoma originating from an active bleeding renal fatty mass (Fig.1). Urgent arteriography showed a long and tortuous venous vessel within the right kidney with extravasation of contrast media (Fig.2). Patient underwent embolisation performed with Onics 20 and Embozene 250 (fibrin glue). Post-procedural contrast-enhanced CT demonstrated that there were no more signs of active bleeding and after some days the patient was discharged from the hospital. Two months later an MRI was performed that showed a right renal mass with high signal intensity on both T1- and T2-weighted acquisitions (Fig.3a, b). Axial T1-weighted acquisitions with fat suppression showed diffuse loss of signal within the renal mass due to its adipous content (Fig.3c). After i.v. administration of contrast media, the renal neoplasm did not show any significant enhancement due to its arterial embolisation and the right perirenal space had a simil-fluid signal intensity due to haematoma (Fig.3d).

Discussion

Renal angiomyolipomas (AML) are benign masses composed of varying proportions of fat, smooth muscle, and thick-walled blood vessels. The relative amount of each tissue varies; a minority (4.5%) of these tumours are classified as minimal fat AMLs, as they contain only microscopically detectable fat [1]. There is an association with Tuberous Sclerosis (80% of patients with Tuberous Sclerosis have renal angiomyolipomas).
Renal AML are most commonly detected as an asymptomatic renal mass often detected as an incidental finding on abdominal imaging; only in a few cases, patients may have symptoms of pain or haematuria due to haemorrhage into the lesion.
However, when the size of renal AML is greater than 4 cm, symptoms may develop in 68–80% of patients. Sudden-onset flank pain is the most common symptom in patients with renal bleeding and haemorrhage leads to hypovolemic shock in one-third of patients presenting with this clinical history. AMLs account for 24% of spontaneous renal haematomas [1, 2].
The role of imaging is important both for the diagnosis and the follow-up.
Angiomyolipomas are difficult to differentiate from renal adenocarcinoma when they do not show any fat content on CT. A confident diagnosis of renal AML can be made when fat content is demonstrated in a renal mass. [2].
Using MRI, the most reliable demonstration of bulk fat within a renal angiomyolipoma can be achieved by comparing images obtained with the same imaging parameters before and after fat-suppression techniques. In-phase and opposed-phase MR imaging is also helpful in the diagnosis of renal AML showing in opposed-phase GRE T1-weighted acquisition a mild decrease in signal intensity of the mass due to the intravoxel coexistence of fat and water protons and the possible presence of high signal intensity spots within the mass that suggest the presence of bulk fat (chemical shift imaging) [3]. The appearance of angiomyolipoma on T2- weighted images is variable and depends on the volume of fat tissue within the lesion [3, 4, 5].
Asymptomatic lesions often require only a clinical follow-up with imaging.
The main indications for the treatment of a renal AML are haemorrhage, pain or reduction of mass effect. The treatment can be minimally invasive or surgical and can be performed in an elective or emergent manner [6]. The minimally invasive treatment by selective arterial embolisation should be considered to spare nephrons [7].

Differential Diagnosis List

Final Diagnosis

Bleeding right renal angiomyolipoma.

URL:	https://www.eurorad.org/case/10363
DOI:	10.1594/EURORAD/CASE.10363
ISSN:	1563-4086