Intrathoracic metastasis (M1a)
Lung
Contralateral lung metastasis are found in 16–28% of patients,
and are considered stage M1a.
If the patient has pulmonary oligometastatic disease,
he can be treated with surgical resection or stereotactic body radiotherapy.
Use of the post-processing tool MIP (maximum intensity projection),
which displays the highest-density voxels from a data set onto a predefined single image plane,
helps detection of small nodules that can otherwise be missed.
Pulmonary lung cancer metastasis tend to be rounded,
multiple,
of varying sizes and have a random distribution Fig. 1.
Fig. 1: Axial chest CT of a patient with left lung cancer shows a round nodule in the middle lobe (arrow) in keeping with pulmonary metastases. Note the interlobular septal thickening in the left lung in the setting of lymphangitis carcinomatous (*).
References: Department of Radiology, University Hospital Santa Lucía
Pleura and pericardium
Pleural and pericardial metastasis usually appear as irregular thichkening or nodules of varying number and size that enhance after injection of contrast medium,
with or without associated effusion.
The presence of pleural or pericardial malignant effusion is also considered metastasis Fig. 2 .
Fig. 2: Coronal contrast-enhanced chest CT in a patient with a confirmed pulmonary adenocarcinoma (*) shows multiple nodules with pleural base in keeping with pleural metastasis (arrows).
References: Department of Radiology, University Hospital Santa Lucía
The use of PET/CT scan may be helpful in unclear cases if it shows an increase in the glucose uptake in pleural and pericardial effussions,
which would be in favor of them being metastatic.
However this technique has false positives if the nodules are too small (typically,
smaller than 1 cm).
Extrathoracic (M1b,
single and M1c,
multiple)
Adrenals
Adrenal metastases are common (up to 20%) and usually accompanied by metastases in other organs,
although they can present as oligometastatic disease.
They tend to appear as rounded necrotic masses,
even though if they are not very big,
they may be mistaken for adrenal adenomas.
For differentiating adenomas from metastasis,
a non-enhanced adrenal CT can be made.
If the density of the lesion is not confirmed to be benign (<10 HU),
the absolute and relative washout values can be calculated.
Other imaging techniques such as adrenal MRI including chemical shift imaging can also be made to try to rule out adrenal metastasis.
However,
the imaging modality of choice when suspecting an adrenal lung cancer metastasis is PET/CT scan,
as it can also detect other hidden metastasis Fig. 3.
Fig. 3: Images of the same patient with known lung cancer.
A. Axial contrast-enhanced abdominal CT shows a hipodense nodule in the right adrenal gland (arrow).
B. PET-CT shows 18-FDG uptake of the right adrenal gland (SUV: 5.5), which supports its malignant nature.
References: Department of Radiology, University Hospital Santa Lucía
Metser and colleagues found that when malignant adrenal lesions were compared with adenomas,
PET data alone using a standardized uptake value (SUV) cutoff of 3.1 yielded a sensitivity,
specificity,
positive predictive value (PPV),
and negative predictive value (NPV) of 98.5%,
92.0%,
89.3%,
and 98.9%,
respectively (Fig.
3).
Bone
Between 5-40% of patients with lung cancer have bone metastasis.
The most frequent site of bone metastases from lung cancer are the rib,
followed by the thoracic and lumbar spine.
The reasons for these sites to be the most affected are the existence of venous traffic branches among lung,
intercostals and vertebral veins,
and the short distance among these organs.
Squamous cell and large cell lung cancers tend to produce osteolytic lesions,
whereas small cell and adenocarcinoma (the most common hystological type to cause them) may produce osteolytic or ostebolastic lesions.
PET/CT is particularly effective for detecting osteolytic bone metastasis in patients with lung cancer,
with sensitivity,
specificity,
PPV,
and NPV of PET/CT of 94.3%,
98.8%,
90.0%,
and 99.3%,
respectively.
This is because PET/CT has the ability to detect early bone metastasis as well as early neoplastic infiltration of bone marrow before they can be seen in CT alone on some occasions. Fig. 4
Fig. 4: Axial CT scan (A) shows a lytic lesion in the anterior aspect of the 5th lumbar vertebra (arrow) in a patient with lung cancer. PET/CT scan of the same patient (B) shows increased 18-FDG uptake of the lesion, which confirms its metastatic nature.
References: Department of Radiology, University Hospital Santa Lucía
Brain
Brain metastasis are present in 20% patients.
They are usually symptomatic and more frequent in the histological subptypes of small cell cancer and adenocarcinoma.
The higher number of metastasis,
the worse outcome.
Contrary to lung cancer metastasis in other sites,
PET/CT has limitations in the evaluation of brain metastases as there is physiologic increased metabolic activity of this organ.
Brain MR Imaging with contrast is the modality of choice for the evaluation of intracranial metastatic disease,
since it may show metastasis that are missed with brain CT Fig. 5 .
Fig. 5: Brain metastasis of lung cancer in three different imaging techniques of the same patient:
A. Brain CT shows supratentorial bilateral vasogenic edema (*).
B. T1 weighted contrast-enhanced magnetic resonance imaging (MRI) shows vasogenic edema (*) and two ring-enhancing lesions (yellow arrosws).
C. PET-CT depicted vasogenic supratentorial edema (*) with lack of 18-FDG uptake in the anatomic region of the known brain metastases.
References: Department of Radiology, University Hospital Santa Lucía
On brain CT or MRI after the administration of intravenous contrast,
they usually appear as ring-enhancing lesions with associated vasogenic edema,
which,
if very extensive,
may cause displacement of anatomical structures Fig. 6 .
Fig. 6: Axial brain CT scan without intravenous contrast (the patient had renal insufficiency) shows a round cystic lesion in the right parietal lobe (blue*) with marked vasogenic edema (yellow *) producing a subfalcine herniation (arrow). A primary lung cancer was found later.
References: Department of Radiology, University Hospital Santa Lucía
Liver
Liver metastasis are present in 5-15% of patients,
and usually coexist with other extrathoracic metastasis.
Its appearance may vary,
even though they usually show washout in the portal phase Fig. 7
Fig. 7: Axial contrast-enhanced CT of the abdomen in portal phase in a patient with lung cancer. There is a hypodense lesion in the upper pole of the left kidney. The value of the pixel count rules out a cystic lesion (blue circle).
Liver metastasis can also be seen (*).
References: Department of Radiology, University Hospital Santa Lucía
Renal
Renal metastases are usually small,
multiple,
bilateral,
wedge-shaped,
less exophytic than other renal tumors,
and located within the renal capsule (bean-type lesion).
When they are present,
other extrathoracic metastasis are usually present too.
Differential diagnosis has to be made mainly with simple cysts,
renal cell carcinomas,
focal pyelonephritis and lymphoma
Fig. 7 .
Fig. 7: Axial contrast-enhanced CT of the abdomen in portal phase in a patient with lung cancer. There is a hypodense lesion in the upper pole of the left kidney. The value of the pixel count rules out a cystic lesion (blue circle).
Liver metastasis can also be seen (*).
References: Department of Radiology, University Hospital Santa Lucía
Others: Pancreatic,
splenic
Pancreatic and splenic metastasis are not frequent.
When they are present,
multiple extrathoracic metastasis are often present too.