PHACE Syndrome: Comprehensive Imaging Guide and Clinical Overview
Overview
PHACE syndrome is a complex neurocutaneous disorder named as an acronym representing its primary clinical features: Posterior fossa brain malformations, large facial infantile Hemangiomas, Arterial anomalies, Coarctation of the aorta and other cardiac defects, and Eye abnormalities. It also sometimes includes sternal defects and supraumbilical raphe anomalies. The name PHACE was coined to encompass this constellation of findings.
PHACE syndrome typically presents in infancy with segmental facial hemangiomas larger than 5 cm, mainly involving the face, scalp, or cervical region. It is a sporadic condition with no clear inheritance pattern described, though genetic contributions remain under investigation.
Key Imaging Features
- Brain MRI showing posterior fossa malformations such as cerebellar hypoplasia or Dandy-Walker variant.
- MR angiography (MRA) of brain, neck, and aortic arch revealing arterial anomalies including narrowed or absent cerebral arteries, arterial tortuosity, and aberrant branching patterns.
- Coarctation or other obstruction of the aortic arch evaluated through echocardiography and confirmed by cardiac MRI and MRA.
- Identification of large facial segmental infantile hemangiomas with typical imaging features on ultrasound and MRI.
- Occasionally, asymmetric enlargement of Meckel’s cave or ventricular abnormalities are noted on neuroimaging.
- Sternal or midline defects can be detected clinically but may be evaluated further with imaging if indicated.
Pathophysiology
PHACE syndrome pathogenesis involves developmental vascular dysgenesis affecting craniofacial and cerebral vasculature during embryogenesis. The large segmental infantile hemangiomas arise from abnormal proliferation of endothelial cells in facial segments deriving from neural crest cells, while arterial anomalies reflect disrupted embryonic artery formation leading to hypoplasia, stenosis, or aberrancies in the aortic arch and cerebral arteries.
Posterior fossa structural defects, such as hypoplasia of the cerebellum, result from disturbed hindbrain development linked to these vascular abnormalities. These malformations contribute to hydrocephalus in some cases, occasionally necessitating neurosurgical intervention like ventriculoperitoneal shunts. The progressive nature of arterial stenoses and coarctation predisposes to ischemic strokes in early childhood if not managed promptly.
Differential Diagnosis
- CLOVES syndrome: Characterized by congenital lipomatous overgrowth, vascular malformations, and epidermal nevi; differs by its truncal-based malformations and absence of posterior fossa brain malformations.
- Sturge-Weber syndrome: Involves facial port-wine stain and leptomeningeal angiomas but lacks characteristic large segmental hemangiomas and aortic arch anomalies seen in PHACE.
- Capillary malformation-arteriovenous malformation (CM-AVM): Features vascular malformations without associated brain structural anomalies typical of PHACE.
- Isolated infantile hemangiomas: Generally smaller, focal, and lack systemic vascular or structural brain anomalies.
Imaging Protocols and Techniques
For suspected PHACE syndrome, a comprehensive imaging workup includes:
- Brain MRI with T1, T2, and FLAIR sequences focused on posterior fossa visualization to identify structural anomalies.
- Time-of-flight (TOF) MRA of the brain, neck, and aortic arch to define arterial anatomy, detect stenoses, hypoplasia, or aberrant vessels critical for stroke risk stratification.
- Contrast-enhanced cardiac MRI and MRA for detailed assessment of aortic arch and cardiac anomalies when echocardiogram suggests abnormalities.
- Use of sedation or anesthesia should be minimized; in infants, physical restraint techniques may be employed to avoid risks associated with sedation.
- Follow-up imaging frequency is individualized: high-risk cases may undergo imaging every 3 months, whereas lower-risk infants may be imaged annually to monitor evolution of vascular anomalies and hemangiomas.
Ultrasound may be used initially for hemangioma evaluation, but MRI/MRA remain the modalities of choice for detailed vascular and brain assessment. Radiologists should carefully evaluate neurovascular anatomy and document key measurements such as arterial diameters and extent of coarctation. Recognition of progressive stenosis or aneurysmal changes over time is crucial for management planning.
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