What is a Phlebolith?
A phlebolith is a calcified thrombus (blood clot) that forms within a vein, most commonly associated with venous malformations, appearing as round calcifications with a laminated structure on imaging. 1
Characteristics and Formation
Phleboliths develop through the following process:
- They originate as thrombi (blood clots) within veins
- Over time, these thrombi undergo calcification
- They commonly occur at sites of arteriovenous microshunts in venous malformations 2
- They typically have a characteristic "onion-ring" appearance histologically, with concentric lamellar fibrosis around a central core 3
Imaging Appearance
Phleboliths can be detected through various imaging modalities:
- Radiography: Appear as round calcifications with laminated structure 1
- Ultrasound: Show as echogenic structures with acoustic shadowing 1
- MRI: Appear as signal voids (areas of signal loss) 2, 1
- CT: Excellent for visualizing phleboliths and differentiating them from other calcifications 1
Clinical Significance
Phleboliths have several important clinical implications:
- Most commonly associated with venous malformations but can occasionally occur in isolation 4, 5, 6
- Generally do not require specific treatment unless associated with symptomatic vascular malformations 1
- Their presence should prompt evaluation for underlying vascular malformations 1
- Can be mistaken for other calcified structures, particularly urinary tract stones in the pelvic region 2, 1
Differential Diagnosis
Phleboliths must be differentiated from:
- Urinary tract stones (particularly in the pelvis)
- Arterial calcifications
- Sialoliths (salivary gland stones)
- Calcified lymph nodes
- Foreign bodies 1
Common Locations
While phleboliths can occur in various locations, they are most frequently found in:
- Pelvic veins 5
- Oral and maxillofacial regions (often associated with hemangiomas) 7
- Occasionally in isolated locations without associated vascular anomalies 4, 6
Clinical Pearls and Pitfalls
- The "soft tissue rim" sign on contrast-enhanced CT can help differentiate ureteral stones from phleboliths 2
- Multiple phleboliths are considered pathognomonic for hemangiomas and vascular malformations in the oral and maxillofacial region 7, 3
- Isolated phleboliths without associated vascular malformations are rare but do occur 4, 5, 6
- When found incidentally without symptoms, observation is the standard approach 1
In summary, phleboliths are calcified venous thrombi that serve as important radiologic markers, often indicating the presence of underlying vascular malformations, though they can occasionally occur in isolation.