The S curve: a novel morphological finding in the internal carotid artery in patients with fibromuscular dysplasia

Vasc Med. 2014 Oct;19(5):356-62. doi: 10.1177/1358863X14547122. Epub 2014 Aug 18.


Fibromuscular dysplasia (FMD) is a non-atherosclerotic vascular disease commonly affecting the renal and internal carotid arteries (ICAs). A previously unrecognized finding is a redundancy of the mid-distal ICA in FMD patients causing an 'S'-shaped curve. Carotid artery duplex ultrasounds were reviewed in 116 FMD patients to determine S-curve prevalence. FMD patients with an S curve were matched to four control patients divided equally into two groups: (1) age and sex-matched and (2) age ≥70 and sex-matched. S curves were present in 37 (32%) FMD patients. Of these, nine (24%) had angiographic evidence of FMD in their ICA only, 13 (35%) had renal artery FMD only, and 15 (41%) had both ICA and renal FMD. Two patients in the age and sex-matched group had S curves (odds ratio 16.86, 95% CI 3.92-72.48; p<0.0001) while 12 (16.2%) patients in the age ≥70 and sex-matched group had S curves (odds ratio 2.42, 95% CI 1.16-5.03; p=0.016). In conclusion, the S curve is a novel morphological pattern of the mid-distal ICA. While the S curve may not be specific, its presence in individuals <70 years old should alert the clinician to the possibility that FMD is present.

Keywords: Doppler ultrasound; S curve; carotid artery; dissection; fibromuscular dysplasia; tortuosity.

MeSH terms

  • Adult
  • Age Distribution
  • Aged
  • Carotid Artery Diseases / diagnostic imaging*
  • Carotid Artery Diseases / epidemiology*
  • Carotid Artery Diseases / physiopathology
  • Carotid Artery, Internal / diagnostic imaging*
  • Carotid Artery, Internal / pathology
  • Case-Control Studies
  • Comorbidity
  • Cross-Sectional Studies
  • Female
  • Fibromuscular Dysplasia / diagnosis*
  • Fibromuscular Dysplasia / epidemiology*
  • Fibromuscular Dysplasia / physiopathology
  • Humans
  • Male
  • Middle Aged
  • Prevalence
  • Prognosis
  • Reference Values
  • Risk Assessment
  • Sex Distribution
  • Ultrasonography, Doppler, Duplex / methods