What Does Lung Base Mean?

Lung base means a process at the bottom of the lungs.  The lungs have left upper and lower lobes and right upper, middle, and lower lobes on the right.  When we say lung base, we mean the bottom of the lower lobes on both sides.  This is a common location for abnormalities.  We will often see an abnormality described as being at the lung base in a report.  This can be described on all types of imaging studies including X-ray, CT and MRI.

What kinds of studies do you see lung bases on?

The lung base or bottom of the lungs can be seen on CT scan of the chest and abdomen.  CT scans of the abdomen will include at least a part of the lung bases.  Sometimes unexpected abnormalities can be seen at the lung bases even on a CT scan of the abdomen when you have no chest symptoms.  The lung bases are included in their entirety on a CT scan of the chest.

What are some of the most common conditions seen at the lung bases?

Many scans will have atelectasis at the lung bases.  This means that a small amount of the lung is airless or collapsed.  This often looks like ground glass densities along the dependent or back part of the lung bases.  This usually is of no consequence and can reverse with deep breathing.  Scarring of lung tissue can have some overlap in appearance and is more serious permanent damage.  This will sometimes be most severe at the lung bases.

We often see nodules at the lung bases or spots.  These are most commonly under a centimeter.  Nodules which are under 6 millimeters often receive no follow up or follow up is optional because they are mostly benign.  Those small nodules between 6-8 millimeters are followed with another scan in 6-12 months.  Nodules above 8 mm may be followed more frequently or worked up with more testing.  The main concern is cancer although scars and inflammatory conditions can also have this appearance.

Pneumonia is common at the lung bases.  Pneumonia is an infection of the lung which results in lung air spaces being filled with pus and liquid.  Pneumonia will look like an area of ground glass or white lung.  It may involve more than the lung bases.  Pneumonia related to aspiration or when swallowed materials go into the lung can occur at the bases in a standing patient.

Lung base means the bottom of the lungs.  It is a common place for abnormalities, some of which are detailed above.    Knowing a process is at the lung bases can help us narrow the diagnostic possibilities.  Clinical history is important when evaluating abnormalities at the lung bases.  More imaging testing may be needed based on the suspected diagnosis.