What are the mimickers of chronic pulmonary thromboembolism and how are they diagnosed and managed?

Mimickers of Chronic Thromboembolic Pulmonary Hypertension

The primary mimickers of CTEPH include in situ pulmonary artery thrombosis, pulmonary artery sarcoma, fibrosing mediastinitis, large vessel pulmonary arteritis (particularly Takayasu's arteritis), and pulmonary vasculitis—all of which can present with similar perfusion defects on V/Q scanning but have distinct imaging characteristics on CT angiography that allow differentiation. 1, 2

Key Mimickers and Their Distinguishing Features

In Situ Pulmonary Artery Thrombosis

• Occurs without preceding pulmonary embolism, typically in patients with underlying pulmonary arterial hypertension, malignancy, or hypercoagulable states 2
• Distinguished from CTEPH by the absence of organized thrombus characteristics and lack of prior PE history 1
• Clinical context is critical: look for underlying conditions predisposing to local thrombosis rather than embolic disease 2

Pulmonary Artery Sarcoma

• Presents as an intraluminal filling defect that can closely mimic chronic thromboembolic disease 1, 2
• Key distinguishing CT features include: eccentric location contiguous with the vessel wall, extravascular extension beyond the pulmonary artery, and heterogeneous enhancement pattern 3, 2
• Often shows progressive enlargement on serial imaging, unlike stable organized thrombus 2
• May demonstrate calcification within the mass 3

Fibrosing Mediastinitis

• Causes extrinsic compression and narrowing of pulmonary arteries rather than intraluminal obstruction 1, 2
• CT shows mediastinal soft tissue infiltration with calcification, particularly in the context of histoplasmosis or other granulomatous disease 2
• Bilateral hilar and mediastinal lymphadenopathy may be present 2

Large Vessel Pulmonary Arteritis (Takayasu's Arteritis)

• Can present with pulmonary artery obstruction mimicking CTEPH but represents an inflammatory vasculopathy 4
• Distinguishing features include: smooth arterial wall thickening, involvement of the aorta and its branches, absence of intraluminal webs or bands, and younger patient age (typically <40 years) 4
• Systemic inflammatory markers are often elevated 4
• Angiography shows smooth tapering and stenosis rather than the irregular contours seen in CTEPH 4

Pulmonary Vasculitis and Sarcoidosis

• Can produce perfusion defects on V/Q scanning similar to CTEPH 2
• CT typically shows additional parenchymal abnormalities, nodules, or ground-glass opacities not characteristic of CTEPH 2
• Clinical context includes systemic vasculitis symptoms or extrapulmonary sarcoidosis manifestations 2

Diagnostic Approach to Differentiate CTEPH from Mimickers

Initial Screening

• V/Q scintigraphy remains the best screening test, showing multiple large mismatched perfusion defects in CTEPH 5
• However, V/Q scanning cannot distinguish CTEPH from its mimickers—all may show abnormal perfusion patterns 2

Definitive Imaging Characteristics of True CTEPH

• Specific diagnostic signs on CT angiography include: ring-like stenoses, webs, slits, chronic total occlusions, and abrupt cut-off of lobar or segmental arteries 3
• Irregularities of vessel diameter and eccentrically located masses contiguous with the vessel wall suggest chronic disease 3
• Direct vascular signs must be present after at least 3 months of effective anticoagulation to confirm CTEPH rather than acute PE 3, 6

Critical Diagnostic Pitfalls

• A relatively normal CT angiogram can occur in CTEPH despite substantial V/Q scan abnormalities, particularly when disease is predominantly distal 5
• Prominent perivascular tissue may be confused with intravascular thromboembolic material 3
• Breathing artifacts can create pseudo-hypoattenuating areas mimicking clot 3
• The diagnosis of CTEPH is often missed on initial CT interpretation—radiologists must actively evaluate for concurrent chronic disease in all cases of acute PE 1

Management Implications

When CTEPH is Confirmed

• All patients require referral to specialized CTEPH centers for multidisciplinary team evaluation 6, 7
• Right heart catheterization is mandatory to confirm mean PAP ≥25 mmHg and pulmonary arterial wedge pressure ≤15 mmHg 6
• Surgical operability assessment determines treatment pathway, with pulmonary endarterectomy offering near-normalization of hemodynamics and mortality as low as 4.7% 6, 7

When a Mimicker is Identified

• Pulmonary artery sarcoma requires oncologic evaluation and surgical resection when feasible 2
• Takayasu's arteritis necessitates immunosuppressive therapy rather than anticoagulation 4
• Fibrosing mediastinitis management focuses on treating underlying infection and managing complications 2
• In situ thrombosis requires treatment of the underlying predisposing condition 2

The key to avoiding diagnostic error is recognizing that multiple conditions can produce similar perfusion defects on V/Q scanning, and that detailed CT angiography interpretation focusing on specific vascular morphology is essential for accurate differentiation. 1, 2