Spider angiomas (SAs), collections of small blood vessels radiating from a central, dilated arteriole that form near the surface of the skin, are  found in 10-15% of healthy adults and young children, as well as in a variety of conditions, including pregnancy, women taking oral contraceptive pills (OCPs),  thyrotoxicosis, and chronic liver disease¹.  

Although the exact mechanism of the formation SAs has not been fully elucidated, several hypotheses have been offered:

• Arteriolar vasodilation caused by estrogen excess due to impaired hepatic metabolism in cirrhosis; ²this is supported by the association of SAs also with other high-estrogen states, such as in pregnancy and OCPs.
• Vasodilatory effects of substance P, a neuropeptide partially inactivated by the liver and elevated in patients with liver disease. ³ 
• Neovascularization promoted by vascular endothelial growth factor and basic fibroblast growth factor released by damaged hepatocytes. ⁴
• Alcohol itself may contribute, as SAs are more commonly seen in individuals with alcoholic cirrhosis than in those with non-alcoholic causes of liver disease. ²

For unknown reasons, in adults spider angiomas most commonly occur in areas drained by the superior vena cava, namely the face, arms, neck, and chest.

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References

1. Khasnis A, Gokula RM. Spider nevus. J Postgrad Med 2002;48:307.         
2. Li CP, Lee FY, Hwang SJ, et al., Spider angiomas in patients with liver cirrhosis: role of alcoholism and impaired liver function. Scand J Gastroenterol 1999;  34: 520-3.https://www.ncbi.nlm.nih.gov/pubmed/10423070
3. Li CP, Lee FY, Hwang SJ, et al., Role of substance P in the pathogenesis of spider angiomas in patients with nonalcoholic liver cirrhosis. Am J Gastroenterol 1999; 94: 502-7.https://www.ncbi.nlm.nih.gov/pubmed/10022654
4. Li CP, Lee FY, Hwang SJ,  et al., Spider angiomas in patients with liver cirrhosis: role of vascular endothelial growth factor and basic fibroblast growth factor. World J Gastroenterol 2003; 9: 2832-5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4612064/ 

Contributed by Camille Mathey-Andrews, Medical Student, Harvard Medical School