Imaging in Hypertension

objectives 

 To describe application of imaging in aetiology  of hypertension.

 To state imaging features of the manifestations of various types of hypertension  and effects of hypertension.

 To understand the applications of imaging in therapeutic measures of hypertension.

Application of imaging in hypertension is as follows

     1.   Secondary hypertension < 35y

2. Malignant hypertension
3. Resistant to drugs
4. Unusual symptoms

 Imaging methods used in the evaluation of hypertension are

  US scan     

  CT  / CTU

  MRI / MRA

  Angiography

  Isotope scan  

  IVU                    

Imaging in Renal hypertension

      1.Parenchymal renal diseases ( medical renal diseases) 

      2.Obstructive uropathy    

      3.Reno vascular diseases 

Imaging in renal  parenchymal renal diseases is mainly carried out by US scans. Sizes of the kidneys are reliably assessed by US. Altered echopattern, increased echogenicity are non specific, but reliable features of US indicating medical renal diseases  such as AGN ( fig 1b), chronic glomerulonephitis and chronic pyelonephritis. Appearances are non specific, thus unable to give a histological diagnosis on US. However chronic parenchymal renal disease will show small renal sizes, compared to acute ones, which will give rise to enlargement of kidneys. Normal kidney sizes vary between 9- 12 cm and less than 9 cm is considered small. Doppler US measures the vascular resistance, which is a known manifestation assessed by US. In parenchymal renal diseases, resistive index ( RI) increases, usually it is more than 0 . 7 ( normal 0.6).

Fig 1a - Normal kidney, sagittal US   

 Fig. 1b - acute/sub acute

Renal parenchymal disease 

Fig 1c - end stage renal disease 


End stage renal disease ( ESRD)

It is characterized by a small scarred kidney of well below 9cm, which is echogenic with altered echopattern ( fig 1c).

Adult Poly cystic kidney disease
This is a well known cause of hypertension, which can be reliably assessed by US scan. Family screening is carried out by US as it an autosomal dominant condition. There can be cysts in liver, spleen, pancreas and even in testis, which can be demonstrated on US.This may be an incidental finding on a CT abdomen as in this patient ( fig 2).  

 

Fig 2 - Adult Poly cystic kidney disease

Imaging in Reno Vascular hypertension

Renovascular hypertension is a well known disease entity evaluated by imaging. The following causes are assessed on imaging methods such as US, CTA, MRA and digital subtraction angiography. 

1. Renal artery stenosis (RAS)

      Which could be atherolosclerotic or due to Fibromuscular hyperplasia, latter being more common in young. Fibromuscular hyperplasia affects mid renal artery where as atherosclerosis affects origins of renal arteries.

2. Diseases of small / medium sized vasculitides

           Polyarteritis nodosa

 

Role of US in Renal artery stenosis

US is considered a screening test. It detects a small kidney,  stenosed main renal artery and or segmental artery with some Doppler US changes due to arterial stenosis.  Colour ( fig 2a, b, c) and spectral Doppler ( fig 2d,e)US  flow pattern of interlobar artery  detects when the stenosis is more than 60 %.

 Fig 2a – normal renal arteries, colour Doppler

Fig 2 b – R / Renal artery stenosis

 Fig 2c – L / RAS

 Fig 2d – Spectral Doppl;er US,Normal

2e – spectral Doppler,RAS 

Isotope scans in Renal artery stenosis

Isotope scans are sensitive in the detection of RAS. It is carried out as a dynamic study to assess the renal vasculature and is done after giving an ACE inhibitor as well to confirm the diagnosis.(fig 3)

Fig 3 – an isotope scan showing R / RAS


Angiography ( DSA) in Renal artery stenosis

Angiography is considered the gold standard in diagnosing RAS. However, now it is performed  mainly when therapeutic angioplasty and stenting  is  considered as a therapeutic option. MR or CT angiography are now performed more common in the diagnosis of RAS when it is clinically or ultrasonically suspected.( fig 4c)

 

 














Fig 4 a- Unilateral  RAS on DSA

Fig 4 b- Bilateral  RAS  on DS

Fig 4 c- Bilateral  RAS on MRA

Fibromuscular hyperplasia
It causes stenosis of mid - distal  renal arteries. It has a characteristic corkscrew appearance compared to smooth narrowing in atherosclerosis.

Fig 5 – R / fibromuscular hyperplasia causing stenosis

Therapeutic interventions  of Renal artery stenosis
 This is carried by way of angioplasty and preferably with stenting following angioplasty ( fig 6a, b, c).

Fig 6a - Pre Angioplasty,mid stream aortogram

6b – selective angiogram

6c -  Post angioplasty dilatation