Mass Effect

Mass Effect :
“effect of a growing mass that results in secondary pathological effects by pushing on or displacing surrounding tissue”

It probably comes as no surprise to people with ADPKD that the sheer size of our kidneys and liver will cause symptoms from pressing on other organs in the abdomen. A study from Korea, published earlier this month, has tried to put some measurements and figures to this phenomenon. They are asking three main questions:

  1. Do enlarged kidneys and liver cause significant mass effect?
  2. Can symptoms be anticipated by measurements of the volume of the kidneys or liver?
  3. How common are symptoms of mass effect?

Owners of an X-box may know “Mass Effect” as a game where your role is to save the galaxy from strange invaders from dark space – so not too different from our battle with cysts! In medical fields mass effect is more commonly used in relation to the way in which a tumour in the brain exerts pressure that distorts the normal brain anatomy. It is also applied to tumours and growths elsewhere.
While kidney and liver cysts are not tumours or growths as such they do exert a pressure on surrounding organs. They compete for space in the abdomen with bowels, stomach, spleen, uterus, bladder and blood vessels. This can trigger symptoms that are not directly related to impaired kidney or liver function. In some cases the other organs may be damaged to the extent they also fail to function normally – such as when ascites develops or bile duct obstruction. These symptoms and signs are the “mass effects” I am talking about.
It probably helps at this point to list symptoms of mass effect due to polycystic kidneys and liver:

  • Abdominal distension and feelings of fullness
  • Early satiety and indigestion
  • Reflux and vomiting
  • Shortness of breath or breathless when lying flat
  • Change in bowel habit and haemorrhoids
  • Prolapse of the bladder and uterus
  • Swelling of the legs from obstruction of the veins and lymphatic vessels
  • Obstruction of bile ducts and blood vessels in the liver
  • Fluid collecting in the abdomen (ascites)

The Korean study was set in a single renal unit and included 461 patients. All had CT scans to measure the total kidney volume (TKV) and total liver volume (TLV). Obviously a tall person will have larger organs in the first place so the volume measurements were adjusted for height (htTKV and htTLV). Height adjusted total volumes are stated in “millilitres per metre or ml/m”.

Other measurements included blood tests for renal and liver function with estimations of glomerular filtration rate (GFR). These are the more standard measurements taken at clinic visits.  For each patient the medical records were reviewed for a history of symptoms and signs that could be attributable to mass effect from the enlarged kidneys and liver. In addition 253 patients also completed questionnaires designed to elicit symptoms from pressure, including pain and disturbed bowel function.
The focus of the analysis in the paper is on liver volumes.  They did not find a clear relationship of kidney volume with symptoms of mass effect.

The normal height-adjusted liver volume (htTLV) for a Korean is 850ml/m (a figure arrived at from examining deceased liver donors)
The measured liver volumes in the study population ranged from 500ml/m to over 5,000ml/m.
From the study measurements the paper classifies liver enlargement as

  • Mild – less than 1600ml/m
  • Moderate – between 1600 and 3200ml/m
  • Severe – over 3200 ml/m

As an aside, these parameters differ from those used in the HALT-PKD trials where severe liver enlargement was anything above 1800ml/m. There is no standard definition for degrees of liver enlargement when assessed by htTLV.
By the Korean definitions 5% had severe liver enlargement and most of these were female. A further 12% had moderate enlargement, again with a preponderance of females.
Because of the difference in classification this study cannot be compared directly with others that have included measurements of liver volume. However this study does support the observations that, in patients with ADPKD, there is a higher prevalence of liver cysts in women and that the numbers and volume of these cysts tend to increase with advancing age.
Using data from the questionnaires and medical records the study authors conclude that the liver volume relates directly to the symptoms, so an increase in htTLV is associated with an increased likelihood of pressure-related symptoms.

This is interesting because recently several papers have suggested using height-adjusted total kidney volume (htTKV) as a measure for progression of disease. But this study strongly suggests that it is the liver volume (htTLV) that is more closely related to the experience and progression of symptoms.  In fact it highlights the fact that many of the symptoms that actually bother us as PKD patients are not related directly to the kidney function. Perhaps using the GFR to assess ADPKD should be supplemented by measurements of both htTKV and htTLV.

  • 47% of study patients experience abdominal fullness and discomfort
  • 44% felt breathless due to the enlarging organs
  • 23% could eat only small amounts due to feeling full
  • 20% had leg swelling from obstruction of leg veins and lymphatics
  • 60%+ had pains in back and flanks that was not attributable to cyst rupture or infection

The authors of this paper conclude that patients with htTLV above 1600ml/m are very likely to suffer from mass effect and to require therapeutic intervention for this. So this value serves as an appropriate cut-off point above which patients deserve referral to hepatic specialists and centres equipped to deal with liver enlargement.
I think it is an important paper. Currently it is not regular practice to measure either kidney or liver volumes. This is only undertaken in clinical studies or in some centres for investigations of intractable symptoms. Disease management can tend to focus on measurable abnormalities but should also address patient symptoms. Perhaps by introducing a measurement that has been shown to relate directly to symptoms experienced this will validate the previously less quantifiable symptoms of mass effect in ADPKD.
Reference:
Kim H, Park HC, Ryu H, Kim K, Kim HS, Oh K-H, et al. (2015) Clinical Correlates of Mass Effect in Autosomal Dominant Polycystic Kidney Disease. PLoS ONE 10(12): e0144526. doi:10.1371/journal.pone.0144526

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