Unilateral Opaque Hemithorax

Dharshan Vummidi, MD

Jeffrey P. Kanne, MD

DIFFERENTIAL DIAGNOSIS

Common

Pleural Effusion
Empyema
Hemothorax
Pneumonectomy
Community Acquired Pneumonia

Less Common

Endobronchial Tumor
Non-Small Cell Lung Cancer
Small Cell Lung Cancer
Pleural Metastasis

Rare but Important

Pulmonary Agenesis
Fibrous Tumor of Pleura
Malignant Mesothelioma

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Chest wall
- CT and MR usually definitive
- Absent mediastinal shift
- Associated osseous lesions (e.g., fracture with chest wall hematoma)
Pleural
- Obtuse margins with pleural interfaces
- Contralateral mediastinal shift
- CT and MR usually definitive
Pulmonary
- Acute margins with pleural surface
- Mediastinal shift varies depending on etiology
- CT usually definitive

Helpful Clues for Common Diagnoses

Pleural Effusion
- Contralateral mediastinal shift
- Atelectasis of underlying lung
- Meniscus sign: Lateral concave border where effusion meets costal pleura
- Downward displacement of hemidiaphragm on left
Empyema
- Lenticular shape
- Nondependent location with clear demarcation from adjacent lung
- Split pleura sign
  - Pleural fluid separates enhancing visceral and parietal pleura
  - Not specific for empyema: Occurs with any form of pleural inflammation
- Haziness in adjacent extrapleural fat
- Compresses adjacent lung and vessels
- Presence of gas in absence of thoracentesis
- Contralateral mediastinal shift
Hemothorax
- High-attenuation pleural fluid (> 50 HU)
- Usually unilateral
- Blunt or penetrating trauma
- Iatrogenic
- Spontaneous causes include rupture of aneurysms, coagulopathy, pleural metastases, and pleural endometriosis
Pneumonectomy
- Pneumonectomy space fills with fluid within 30 days
- Ipsilateral mediastinal shift
- New or increased gas in existing pneumonectomy space indicates bronchopleural fistula
Community Acquired Pneumonia
- Lobar consolidation
  - S. pneumoniae most common
  - TB, H. influenzae, Legionella less common
- Parapneumonic effusion
  - Can develop into empyema

Helpful Clues for Less Common Diagnoses

Endobronchial Tumor
- Whole lung collapse less common than lobar collapse
- Primary lung carcinoma: Squamous cell carcinoma most common
- Metastasis: Breast, colon, and renal cell carcinoma; melanoma
- Ipsilateral mediastinal shift
Non-Small Cell Lung Cancer
- Extrinsic compression of main bronchus
  - Primary tumor, lymph node metastases, or both
Small Cell Lung Cancer
- Extrinsic compression of main bronchus
  - Bulky lymph node metastases common
- May also invade mediastinum
Pleural Metastasis
- ∽ 90% of all pleural neoplasms
  - Lung carcinoma leading cause
  - Breast, ovary, and gastric carcinomas and lymphoma also common causes
- Usually multiple
- Can simulate benign pleural disease
- Nodular, circumferential, and mediastinal pleural involvement suggestive of malignancy
- Associated pleural effusion common
- Can have lung or thoracic lymph node metastases

Helpful Clues for Rare Diagnoses

Pulmonary Agenesis
- Complete absence of lung with no bronchial or vascular tissue
- Often associated with other congential anomalies, resulting in neonatal death
- Adults with isolated pulmonary hypoplasia often asymptomatic
- Identical imaging appearance to patients with childhood pneumonectomy
Fibrous Tumor of Pleura
- 5-10% of primary pleural neoplasms, 12% malignant
  - Imaging alone cannot determine whether malignant or not
- Peak incidence: 6th and 7th decades
- Approximately 50% patients symptomatic
  - Clubbing (4%)
  - Symptomatic hypoglycemia (4-5%)
- Radiography
  - Solitary peripheral pleural mass with smooth margins
  - May develop within pulmonary fissure
  - Can change orientation with changes in patient position
- CT
  - Smaller tumors homogeneous
  - Larger tumors heterogeneous with necrosis, cystic degeneration, and hemorrhage
  - Calcification (7-25%) (more common in larger tumors)
  - Has smooth margins, abuts pleural surface, and may form obtuse angles with adjacent pleura
  - Intense, uniform enhancement except in areas of necrosis
- MR
  - Fibrous tissue: Low to intermediate signal intensity on T1- and T2-weighted imaging
  - Cystic degeneration, necrosis, myxoid: Foci of high T2 signal intensity
  - Low signal septa on T2-weighted imaging
  - Blood products: T1 and T2 signal intensity vary depending on age of hemorrhage
Malignant Mesothelioma
- Most result from asbestos exposure
  - Latency of up to 40 years
- Can simulate benign pleural disease
- Nodular, circumferential, and mediastinal pleural involvement suggestive of malignancy
- Mediastinum relatively “fixed” with little or no shift
- Associated pleural effusion may be present
- Extrapleural spread
  - Chest wall, mediastinum, diaphragm