Metastases

Melissa L. Rosado-de-Christenson, MD, FACR

Key Facts

Terminology

Lung most common site of metastases
Pathways: Hematogenous, lymphatic, endobronchial

Imaging Findings

Multifocal bilateral pulmonary nodules
- Peripheral, basilar predominant
- Variable size
- Spherical shapes; smooth, lobular, or irregular margins
- Ground-glass opacity and mixed attenuation nodules
Lymphangitic carcinomatosis
- Smooth or nodular thickening of interlobular septa
- Peribronchovascular thickening
Rare: Solitary nodule, cavitation, calcification

Top Differential Diagnoses

Multifocal Pulmonary Nodules
- Vasculitis, septic emboli, lymphoma
Lymphangitic Carcinomatosis
- Sarcoidosis, silicosis

Pathology

Mechanical arrest model: Metastases are 1st established in filtering organ
Environmental model: Metastases occur in environments favorable for growth

Clinical Issues

Death from malignancy usually attributable to metastatic disease
Metastasectomy for early metastases to prevent systemic disease

Axial CECT shows multiple bilateral peripheral well-defined lung nodules from hematogenous metastases. Note the feeding vessel sign

Axial NECT shows lobular multifocal peripheral nodules and masses of various sizes from hematogenous metastases from adenoid cystic carcinoma.

TERMINOLOGY

Definitions

Metastasis: Spread of disease from 1 organ to another nonadjacent organ or body part
- Used to describe spread of malignant neoplasms and infections
Ability to metastasize is hallmark of malignancy
Metastatic pathways: Hematogenous, lymphatic, and endobronchial
Proposed mechanism of hematogenous metastases
- Invasion of vascular structures by tumor cells
- Transport of tumor cells in bloodstream
- Arrest of tumor cells in filtering organ
- Adherence to vessel walls and subsequent extravasation into tissues
- Micrometastasis
Lung is most common site of metastases: Up to 50% at autopsy
- Filtering organ; receives systemic venous drainage
- “Seed and soil” hypothesis of chemokine-modulated “homing” of tumor cells to specific organs

IMAGING FINDINGS

General Features

Best diagnostic clue: Multifocal bilateral pulmonary nodules &/or masses
Patient position/location
- Lung bases
- Lung periphery; subpleural; outer 1/3 of lung
Size: Variable; 2-4 mm (miliary) to several centimeters
Morphology
- Spherical with smooth margins
- Also lobular and irregular-shaped

CT Findings

Multifocal bilateral pulmonary nodules and masses
More numerous in lung bases (dominant pulmonary arterial flow) and subpleural lung periphery (outer 1/3)
Variable size
- Miliary nodules: Thyroid cancer, renal cell cancer, and melanoma
- Large masses: Sarcomas, colon, and renal cancer
Morphology: Typically spherical
Margins: Well defined, smooth, lobular, irregular
Attenuation: Typically solid nodules
- Ground-glass nodules: Hemorrhagic metastases, endobronchial dissemination, metastatic adenocarcinoma
- Mixed attenuation nodules: Solid nodule surrounded by ground-glass; CT halo sign
Random or uniform distribution of nodules with respect to normal structures
Feeding vessel sign; association of nodule with pulmonary artery
Variable attenuation
- Most are solid nodules
- Ground-glass nodules: Metastatic adenocarcinoma
- Nodules with surrounding ground-glass; hemorrhagic lesions
Lymphangitic carcinomatosis
- Advanced adenocarcinoma
- Hematogenous or lymphatic dissemination
- Smooth &/or nodular thickening of interlobular septa
  - Peripheral reticular opacities
  - Central polygonal arcades
- Thickening of peribronchovascular interstitium
  - Prominent central dot; thick centrilobular bronchovascular bundle
- Asymmetric involvement (50%)
- Normal pulmonary architecture
- Lymphadenopathy (30-50%), pleural effusion (30%)
Unusual manifestations
- Solitary nodule (2-10%)
  - Colon and kidney primaries, melanoma, sarcoma
  - New primary lung cancer must be excluded
- Cavitation (4%): Typically from central necrosis
  - Cavity walls usually thick and nodular
  - Squamous cell carcinomas: Head & neck and cervical cancer
  - Adenocarcinomas and sarcomas
  - Treated metastases
  - Metastatic osteosarcoma may result in spontaneous pneumothorax
- Calcification typically in bone-forming neoplasms
  - Osteosarcomas, chondrosarcomas; also mucinous adenocarcinomas
- Endobronchial metastases (2%)
  - Typically renal cell carcinoma; also melanoma, breast cancer
  - May mimic central primary lung cancer
  - May produce mucus plugs, atelectasis, postobstructive pneumonia
- Intravascular tumor emboli
  - 2.5% of autopsied malignancies
  - Occlusion and enlargement of pulmonary arteries by tumor
  - Branching nodular enlargement of small and medium-sized pulmonary arteries
Other thoracic metastases
- Pleural metastases
  - Pleural effusion, exudate, may be large
  - Solid pleural nodules
  - Pleural effusion and solid pleural nodules
  - Circumferential nodular pleural thickening
- Lymphadenopathy
  - Genitourinary, breast, head and neck primaries, melanoma
  - Typically right paratracheal; other lymph node groups affected

Radiographic Findings

Pulmonary nodules
- Multifocal, bilateral, lower lobe predominant
- Well-defined or ill-defined margins
- Variable size
- Rarely: Solitary nodule, calcification, cavitation, endobronchial metastasis
Lymphangitic carcinomatosis
- Asymmetric reticular opacities
- Thick interlobular septa; Kerley B lines
- Pleural effusion; lymphadenopathy
Pleural metastases
- Pleural effusion
- Pleural masses
- Circumferential nodular pleural thickening
Mediastinal lymphadenopathy
- Genitourinary malignancies, breast cancer, head and neck cancer
- Right paratracheal lymphadenopathy