case studies

Renal Angiomyolipoma

A renal angiomyolipoma is a generally benign tumour than contains blood, muscle and fat, giving it a mixed appearance on all imaging modalities. Most benign tumours of this variety are slow growing but can become very large and can cause haemorrhaging and pain. Treatment normally consists of a full or partial nephrecomy or embolisation of the blood supply (Nelson, 2002).

Clinical history
This study involves a 27 year old female who was obese, finding breathing difficult and feeling progressively unwell. A chest X-ray revealed a suspected pulmonary embolism. This was confirmed by a Nuclear Medicine perfusion study. She was prescribed the anticoagulant drug Warfrin. Two weeks later she developed haematuria. Ultrasound revealed a large non-specific solid mass 7-8cm on the lower pole of the right kidney. CT demonstrated that the tumour had mixed components and the post contrast scans demonstrated that the tumour had a blood supply confirming an angiomyolipoma.

Laparoscopic Heminephrectomy was not suitable due to the patient’s weight and no guarantee of complete tumour removal due to obscuring fatty tissue. Surgically the only other option was to remove the kidney completely. Instead renal embolisation of the supplying artery was performed under fluoroscopic X-ray control. CT repeated two weeks later showed that the tumour had reduced in size from 8cm to 5cm in diameter. The CT scan could not adequately demonstrate the renal arteries and thus the blood supply to the tumour.

3D contrast enhanced MR angiography (CE-MRA) was therefore used to assess the blood supply to the lower pole of the kidney and tumour. The ‘spirale embolisation’ coils used for renal embolisation were MRI compatible being made of Platinum and are non-ferromagnetic (Shellock & Kanal, 1996; Bracco, 2002). CE-MRA eliminates respiratory movement using short acquisition times (Maki et al, 2000). 3D acquisitions can be produced in 30 seconds, or less, allowing all the data to be collected in a single breath, potentially achieving maximum arterial enhancement and minimal venous (Mitsuzaki et al, 2000).

Technique

• 3 plane localiser.
• To optimally visualize the aorta and in preparation for the test bolus, a sagittal slice was prescribed superimposing the aorta on a coronal/axial slice of the 3 plane localiser. A 2D multiphase fast spoiled gradient echo sequence approx 15 mm thick was run repeatedly approximately 30 times. For every second of scanning one slice was reconstructed.
• A coronal 3D volume acquisition (see Table 1) was performed prior to contrast administration (to be used as a mask).
• The sagittal 2D multiphase sequence was repeated as the radiologist injected the test bolus (approx 2 ml sec-1) followed by a saline bolus.
• Peak enhancement was calculated using a “region of interest” placed over the aorta (time to peak).
• The delay time was calculated using Equation 1.

Equation 1

DELAY TIME = TIME TO PEAK + PERFUSION TIME / 2 – SCAN TIME / 2
(General Medical Systems, 2000)

• The coronal 3D volume acquisition was repeated with the patient given breathing instructions for the appropriate delay time (see Equation 1).
• Post processing of the contrast enhanced sequence was then performed (see Figures 1 and 2).

Discussion
MRI renal angiography clearly demonstrated the blood supply to both kidneys without any artefact from the platinum coils (see Figures 1 and 2). The angiomyolipoma was not optimally visualised on the fat saturated images however the raw data demonstrated that there was no blood supply to the tumour, and only directly to the lower pole of the kidney. The technique confirmed the success of renal embolisation stopping the angiomyolipoma from growing.

Alison Burnham
MRI Technologist North Region (case study completed in part fulfilment for PgDip MRI)


References
Bracco (2002) Balt Extrusion Spirale® Platinum Coils information sheet.
Hilfiker, P et al (2000) Partial Fat-Saturated Contrast-Enhanced Three-Dimensional MR Angiography Compared with Non Fat-Saturated and Conventional Fat-Saturated MR Angiography Radiology 216, 298-303.
Maki, J et al (2000) Contrast-Enhanced Mr Angiography Applied Radiology Supplement 29, 3, 5-20.
Mitsuzaki, K et al (2000) Abdomen, Pelvis and Extremities: Diagnostic Accuracy if Dynamic Contrast-Enhanced Turbo MR Angiography Compared with Conventional Angiography – Initial Experience Radiology 216, 909-915.
Nelson, C (2002) Contemporary Diagnosis and Management of Renal Angiomyolipoma Journal of Urology 168, 4, 1315-1325.
Shellock, F & Kanal, K (1996) Magnetic Resonance. Bioeffects, Safety and Patient Management 2nd ed, London: Lippincott Williams & Wilkins.
Volk, M et al (2001) Renal Time Resolved MR Angiography: Quantitative Comparison of Gadobenate Dimeglumine and Gadopentetate Dimegumine with Different Doses Radiology 220, 484-488.
Whitley, A et al (1999) Clarke’s Special Procedures in Diagnostic Imaging Oxford: Butterworth-Heinemann.

Table 1
3D CE-MRA Renal Arteries GE 1.5T SIGNA LX
Fast TOF Spoiled GRASS
TR 6.1
TE 2.8
FOV 26cm x 26cm
Matrix 256 x 128
NEX - 1
BW 31.2 khz
TI 30
Flip Angle 30°

Other software options
Zip 512 and Zip 2, Variable Bandwidth, Special fat suppression, Fastest Turbo mode

Printer friendly version

Back >>