Segmental low-density area on contrast-enhanced CT is a possible clue to diagnosing branch artery fibromuscular dysplasia

Fibromuscular dysplasia can cause renovascular hypertension. Since fibromuscular dysplasia may be underdiagnosed, precise diagnosis and management are crucial, especially for young women. A 20-year-old woman with hypertension and hypokalemia was referred to our hospital for further evaluation of secondary hypertension. At the previous hospital, her blood pressure was 160/110 mmHg and the serum potassium level was 2.9 mEq/L. The equilibrium phase on contrast-enhanced computed tomography revealed a low-density area in the upper median portion of the right kidney. On admission to our hospital, her blood pressure was 141/96 mmHg under 5 mg of amlodipine. Laboratory tests revealed plasma renin activity of 11.3 ng/mL/h and plasma aldosterone concentration of 117.1 pg/mL. Renal venous sampling of active renin concentration showed a right-to-left renin ratio of 3.13, confirming a significant increase in renin secretion from the right kidney. Selective reno-angiography detected focal stenosis with adjacent aneurysmal dilation and tortuosity in the proximal branch of the right renal artery. She was diagnosed with branch artery fibromuscular dysplasia and successfully treated with percutaneous transluminal angioplasty. After the treatment, she was free from hypertension and hypokalemia without any medications. Since branch artery fibromuscular dysplasia is sometimes difficult to diagnose, contrast-enhanced computed tomography can be a promising diagnostic tool as shown in this case. Concerning treatment, our patient was treated with percutaneous transluminal angioplasty, which should be considered for women of reproductive age because recommended antihypertensive medications can be teratogenic even in the first trimester of pregnancy.