Split Renal Function in a Pelvic Kidney

This is an interesting case in that it involved a patient to be injected with two different renal imaging agents:  DTPA and DMSA.

The radiation oncologists wanted to asses the renal function within this patient, prior to having radiation therapy for endometrial cancer.  The big problem was that the patient has a left pelvic kidney, and they feared that it would be ablated during the treatment.  The CT image below details where the kidney lies within the pelvis.

Fig. 1  Sagittal slice of the patient.  Note the ovoid shaped organ on the bottom right of the image just below the sacrum.

The assessment of renal function in our department generally includes the determination of glomerular filtration rate (GFR) and the split renal function (differential renal function) to help the clinicians determine the implications of residual kidney function if a kidney or kidneys are irradiated.  It is also used to determine whether a person is a good candidate for kidney donation, since our hospital is a major organ transplant centre.  The assessment of renal function is a routine procedure for us.  

We perform our renal scans mainly with DTPA, along with corresponding blood samples at time 0 pre-injection, 1 hour post injection and at 3 hours post injection.  We combine this with the Gates analysis method to get an idea of the overall kidney function.  The images below are what we have obtained using the DTPA and blood sampling method.  All dynamic and static images with respect to the kidneys are performed in the supine position.

Fig. 2  Both camera and blood sampling methods are used to determine the GFR.  Regions of interest (ROI's) are drawn over the kidneys, bladder and aorta as per protocol.  Associated background regions are drawn corresponding to each kidney.

Fig. 3  Split renal function (differential) is primarily determined by the camera method.

Fig. 4  The renal dynamic and static images are made into reports to assess drainage from the kidneys as well as to determine the quality of the injection (ie. an interstitial injection?).  However if you look carefully on the top row of images the left pelvic kidney, over time, becomes obscured by the bladder.

We perform continuous imaging over a 20 minute period and then static views of pre and post void kidneys (standing), along with the injection site to assess for residual activity.  

In this case here, as you can see from the images above, the assessment of the right kidney seems to be straight forward, but the problem is the assessment of the left pelvic kidney.  In Fig. 3, over time, it becomes obscured by the bladder.  

(Note, I have tried to load the dynamic acquisition to demonstrate this more clearly, but could not get the correct intensity to illustrate this event)

The problem is, our reporting radiologist could not be confident in reporting the GFR values nor the split renal function, since the regions of interest (ROI's) would incorporate the expanding bladder and would result in an inaccurate estimation of these values.

Essentially our reporting radiologist spoke with the requesting radiation oncologists to consult them with regards to the imaging.  To make a long story short, in the end, the GFR values were not as important as the split renal function.  Thus to avoid the bladder uptake, DMSA was used to scan the kidneys again and a geometric mean was used to determine the split renal function.  Below are the images of the DMSA scan.

Fig. 5  Anterior and posterior images of the kidneys were obtained using DMSA.  A geometric mean was used to better estimate the split renal function.  Imaging was performed in the supine position.

The use of the DMSA essentially limited the amount of bladder activity seen, but provided good parenchymal imaging to allow for the split renal function to be calculated.

Takayasu Arteritis and PET/CT

Takayasu arteritis is one of the indications that we perform an F18 FDG PET/CT scan on, primarily as a research protocol.  This is one of those research studies that we do not do very frequently but once in awhile they pop up on our list.  

What is interesting about this condition, besides the name, is that this is a rare condition that causes vasculitis in the large vessels, such as the aorta and it's branches.  

The history of Takayasu arteritis is pretty interesting as well.  Originally this vascular disease was reported by Dr. Mikito Takayasu, an ophthalmologist in 1908 at the 12th Annual Meeting of the Japan Opthalmology Society. It basically came about with the appearance of "coronary anastomosis" in the eyegrounds and arteriovenous anastomosis around the papila of a 21 year old woman that Dr. Takayasu was examining.  Further investigation lead others to report "pulselessness" in their patients which is another clinical feature.  The radial, brachial and carotid pulses are absent in these patients as the result of the ischemic cerebrovascular circulation.  There's more, but if you click on the link at the start of this paragraph, you can read the rest.

So here is what it looks like in PET:

Fig. 1  FDG PET imaging of a patient with Takayasu arteritis.  Abnormal increased activity are identified along the brachiocephalic and proximal right and left common carotid arteries.

Fig. 2  A fused image denoting the areas of uptake with anatomical features.

Fig. 3  Sagittal fused image with uptake through the common carotid artery.

The preparation for the Takayasu arteritis scans are fairly similar to the other oncological preps that we do in the department except for the fact that we scan with the arms down, we wait for a 90 minute uptake (since the appearance of the inflamed arteries are very subtle thus maximizing the uptake time is essential) and we use an ideal body weight (IBW) calculation.  The cut off glucose measurement is around 11.0mmol/l.  This is slightly higher than the normal cut off of 9.8mmol/l for the rest of our scans.  Imaging is taken from the base of the skull to mid thigh, but 4 minutes per bed for the PET as oppose to the 3 minutes per bed with most of our oncological studies.

As you can see in Fig. 1, there is abnormal increased activity identified along the brachiocephalic and proximal right and left common carotid arteries.  There is also increased activity in the descending aorta at the L2-L3 vertebra, which I did not capture on my screen shots.  PET/CT would probably not be the first choice in terms of imaging with a suspected case of Takayasu arteritis, the more likely options would be CT angiography or MRI to examine the nature of the large vessels.