What is a Phlebolith?
A phlebolith is a benign calcified thrombus (blood clot) that forms within veins, most commonly in the pelvic region, and requires no treatment unless associated with an underlying symptomatic vascular malformation. 1, 2
Definition and Pathophysiology
- Phleboliths are composed of calcified laminated fibrous tissue with a surface layer continuous with vein endothelium 2
- They occur at sites of microshunts in venous malformations, representing organized and calcified thrombi within dilated veins 3, 1
- Histologically, they consist of calcified thrombi that have undergone lamination and mineralization over time 2
Clinical Significance and Prevalence
- Phleboliths are extremely common, occurring in 38.9%-48% of adults, with increasing prevalence after age 40 2
- They affect both genders equally and are more commonly seen in individuals from economically developed countries 2
- Phleboliths are benign findings that do not cause symptoms themselves and require no treatment 1, 2
- They may be associated with underlying venous malformations or diverticulitis 2
Imaging Characteristics
On Plain Radiography:
- Appear as rounded calcifications, often with a characteristic radiolucent center (seen in 66% of cases on X-ray) 2, 4
- Multiple phleboliths are typically present, especially in the pelvic region 3
On CT Imaging:
- Despite appearing with radiolucent centers on X-rays, 99% of phleboliths fail to show a low-attenuation center on routine CT 4
- Phleboliths demonstrate lower Hounsfield unit enhancement (160-350 HU) compared to ureteral stones 2
- The "comet-tail sign" (21%-65% sensitivity, 100% specificity) suggests a phlebolith rather than a ureteral stone 5, 2
On Ultrasound:
- Appear as echogenic structures within venous malformations 3, 1
- Multiple anechoic spaces with echogenic phleboliths are characteristic of venous malformations 3
On MRI:
- Appear as signal voids within venous malformations 6
- MRI with contrast is recommended for proper characterization when phleboliths are associated with vascular malformations 1, 6
When Treatment is Needed
Treatment is only indicated when phleboliths are associated with symptomatic venous malformations, not for the phleboliths themselves. 1
- Management depends on the underlying vascular malformation and associated symptoms 1
- May involve interventional embolization/sclerotherapy and/or surgical intervention over years for symptomatic venous malformations 1
- The American College of Radiology recommends MRI evaluation for proper characterization when venous malformations are suspected 1, 6
Important Clinical Pitfall
- The primary clinical significance of phleboliths is their potential to be mistaken for ureteral stones on imaging, particularly in patients with flank pain 3, 5
- The "rim sign" (circumferential ureteral soft tissue edema) with 50%-77% sensitivity and 92%-100% specificity suggests a ureteral stone rather than a phlebolith 5, 2
- When CT is inconclusive, contrast-enhanced CT or CT urography can help differentiate phleboliths from ureteral stones by demonstrating the "soft tissue rim sign" around true stones 3