HRCT LUNG

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					Approach to nodular lesions on
            HRCT
     Basic anatomy
for HRCT interpretation
Airways
Arteries and veins
Lymphatics
Interstitium
      Primary pulmonary lobule
• The primary pulmonary lobule consists of
  alveolar ducts, alveolar sacs and alveoli

• Approximately 30–50 primary pulmonary
  lobules can be found in one secondary
  pulmonary lobule.
                          ACINUS
• Acinus is the portion of lung distal to a terminal bronchiole
  and supplied by a first-order respiratory bronchiole or
  bronchioles.



• The reported number of acini in one secondary pulmonary
   lobule varies considerably in different studies and numbers
  are found between 3 and 12
    The secondary pulmonary lobule

• The smallest functional unit of lung structure

• Marginated by connective tissue septa

• Irregularly polyhedral in shape

• 1 to 2.5 cm in diameter in most locations
               Components

• Interlobular septa.

• Centrilobular structures.

• Lobular parenchyma and acini
Interlobular septae and centrilobular central artery
Venule visualisation is indirect evidence of visualisation of
                    interlobular septae
Pulmonary edema with interlobular septal thickening
           Centrilobular structures


• Centrilobular artery

• Centrilobular bronchiole and its divisions

• Supporting connective tissue
         Normal measurements

• Secondary lobular artery and bronchiole -1 mm
  in diameter.

• Intralobular terminal bronchioles and arteries -
  0.7 mm in diameter.

• Acinar bronchioles and arteries range from 0.3
  to 0.5 mm in diameter.
 Appearance of intralobular artery


• A linear, branching, or dot like opacity.

• Within the centre of a lobule or within 1 cm of
  the pleural surface.
    Definition – HRCT nodule.


Rounded opacity, well defined or ill defined
with size not more than 3 cm in diameter
             HRCT NODULES
• Size

• Appearance

• Attenuation

• Distribution
                             Nodule size

• Miliary nodule -(1-3 mm).
• Micronodule. – (3 - 7 mm).
 Fleischer Society has recommended that “micronodule” be used to refer to nodules no
 larger than 7 mm in diameter, but generally this term should be reserved for nodules less
 than 3 mm in diameter.

• Small nodule -Smaller than 1 cm.

• Large nodule – 1- 3 cm.
• Mass ( > Mass).
       NODULE APPEARANCE


Predominantly interstitial or predominantly air
space
                    • Airspace nodules are usually caused
                      by a replacement of alveolar air by
                      fluid and/or cells.
Air space nodules

                    • Airspace nodules can have a soft
                      tissue density or a ground-glass
                      density and can be sharply defined but
                      are usually ill defined.

                    • Airspace nodules are mostly located
                      near the centre of the secondary
                      pulmonary lobule.

                    • when disease progresses, involve the
                      entire lobule.
Ill defined airspace nodules - Hypersensitivity pneumonitis
Well defined airspace nodules -Acute viral bronchilolitis
Merging of airspace nodules can be
responsible for the development of larger
nodules and areas of ground-glass opacity and
lung consolidation
    Differential diagnosis for airspace
                  nodules

Infectious
• Bronchiolitis
• Bronchopneumonia
• Tuberculosis
• Mycoplasma
• Aspergillus
• Bronchoinvasive aspergillosis
Smoking related parenchymal lung disease

• (RB-ILD)
Others
• Hypersensitivity pneumonitis
• Organising pneumonia.
• Bronchio alveolar carcinoma
• Pulmonary oedema
• Pulmonary haemoaspiration
• Cystic fibrosis
• Allergic bronchopulmonary aspergillosis
               TREE IN BUD
• Reflects the presence of dilated centrilobular
  bronchioles

• Lumina impacted with mucus, fluid, or pus.

• Associated with peribronchiolar inflammation
Pathogenesis
                Interstitial nodules
• Interstitial nodules are usually caused by a nodular cellular
  proliferation in the interstitium.



• Interstitial nodules are mostly sharply defined and have in most
  cases a soft-tissue attenuation.



• Most interstitial nodules are related to diseases that show a
  vascular or a (peri)lymphatic distribution, although some of
  them are located in the interstitial tissue of bronchiolar walls.
Nodule attenuation
     Differentials for high attenuation
             nodules on HRCT
•   Infections.
•   Lung metastases
•   Chronic pulmonary hemorrhage
•   Pneumoconiosis.
•   Metastatic calcifications
•   Pulmonary alveolar microlithiasis
Axial CT scans shows multiple small calcific PNs due to old healed
histoplasmosis
                     Calcispheres within alveoli (consist of
Pulmonary alveolar      calcium phosphate)
microlithiasis
                     • Very rare
                     • 20-50 years of age
                     • Familial incidence in half
                     • Often asymptomatic at diagnosis
                     • Abnormalities progress slowly
                     Radiographs
                     • Dense lungs
                     • Basal predominance
                     • Individual calcified nodules visible
                     • Black pleural line
                     HRCT
                     • Subpleural and perivascular
                        predominance of calcified nodules
                     • Black pleural line = emphysema
         Metastatic calcification




Metastatic calcification in the lungs in a patient with chronic renal failure
          Metastatic calcifications
Calcification due to abnormal calcium and phosphate metabolism
Etiology.
• Hypercalcemia
• Renal failure
• Secondary hyperparathyroidism
• Chronic hemodialysis
• Commonly affects lung
• Apices most often involved (more alkaline)
HRCT
• Opacities often centrilobular
• May be ground-glass opacity
• Not all nodules are calcified.
High attenuation nodules due to   Talc embolism following the post
pulmonary alveolar hemorrhage.    percutaneous vertebral plasty
             Calcified metastasis

• Osteosarcoma, chondrosarcoma.
• Synovial sarcoma, mucin-producing carcinoma.
• Adenocarcinoma, thyroid tumours .
Distribution pattern of the nodules
Perilymphatic nodules                    Centrilobular nodules




                        Random nodules
Perilymphatic distribution of nodules
Centrilobular distribution of nodules
Random distribution of nodules
Small nodules – distribution




 perilymphatic          random   centrilobular
Perilymphatic nodules


            • Pleural surfaces.
            • Interlobular septa
            • Peribronchovascular
              interstitium.
            • Fissures.
   PERILYMPHATIC DISTRIBUTION
• Sarcoidosis

• Silicosis and CWP

• Lymphangitic spread of carcinoma

• Lymphoma

• Lymphoproliferative disease such as lymphoid
  interstitial pneumonia.
Random nodules
Random nodules.
        • Hematogenous
          metastases
        • Miliary tuberculosis
        • Miliary fungal infection
        • Disseminated viral
          infection
        • Silicosis or coal-worker’s
        • pneumoconiosis
        • Langerhans’ cell
          histiocytosis
             Miliary infections


• Recognized tendency to
  predominate in the lung
  periphery and at the
  lung bases.
Randomly distributed nodules in case of GB carcinoma
Randomly distributed cavitating nodules in case langhans of
histiocytosis
Centrilobular nodules with tree in bud
• Bacterial pneumonia with infectious
• bronchiolitis
• Typical and atypical mycobacterial infections

•   Aspiration
•   Allergic bronchopulmonary aspergillosis
•   Cystic fibrosis
•   Diffuse panbronchiolitis
•   Endobronchial neoplasms (particularly
•   bronchioloalveolar carcinoma)
    Centrilobular nodules without tree in
                    bud
• All causes of Centrilobular nodules with tree-in-bud opacity

•   Hypersensitivity pneumonitis
•   Respiratory bronchiolitis and respiratory
•   bronchiolitis-interstitial lung disease
•   Cryptogenic organizing pneumonia
•   Pneumoconiosis' (especially silicosis
•   and coal-worker’s pneumoconiosis)
•   Langerhans’ cell histiocytosis
•   Pulmonary edema
•   Vasculitis
•   Pulmonary hypertension
          Centrilobular distribution
• Reflect the presence of either interstitial or air-space abnormalities.

• May be well-defined or ill-defined.

• Range from a few millimeters to about 1 cm in size.

• A single centrilobular nodule or a centrilobular rosette of nodules
  may be visible.

• Nodules are roughly evenly spaced from one another and approach
Centrilobular nodules
           • Do not contact visceral
             pleural surfaces.

           • Usually positioned
             about 5 to 10 mm from
             the visceral pleural
             surface.
Ill-defined centrilobular nodules in a patient with
hypersensitivity pneumonitis
Ill defined centrilobular nodules in patient with cryptogenic
organizing pneumonia
Cases
Sarcoidosis
                Sarcoidosis.

• Nodules ranging in size from several
  millimeters to 1 cm or more in diameter.

• Sharply defined despite their small size.

• Nodules are most frequently seen in
  relationship to the perihilar
  peribronchovascular interstitium.
                               Silicosis




There are pleural nodules ,lymphatic distribution and are in upper lobe
predominantly posterior in distribution
                   Silicosis
•   Well defined.
•   Soft tissue attenuation.
•   Calcification may be present.
•   Symmetric.
•   Posterior and upper lobe predominance.

• Other features – fibrosis , pleural plaques .Egg
  shell calcification in lymphnodes.
                     Lymphangatic carcinoma




These nodules are predominantly located in the subpleural interstitium (also
along the great fissures) and in the interlobular septa (beaded
septa). Some nodules are centrilobular, whereas some interlobular septa show
a more homogenous thickening (linear opacities)
         Lymphangatic carcinoma

• Tumor growth in the lymphatic system of the lungs.
• Usually results from haematogenous spread to the lung later
  interstitial and lymphatic invasion.
HRCT
• Small, well-defined nodules , Soft-tissue density
• Septal lines, subpleural thickening, proximal
  Peribronchovascular thickening
• Combination with nodules and beaded septa
                      Lymphoid interstitial pneumonia




Small, sharply defined nodules are visible, particularly along the right major fissure.
Interlobular septal thickening and nodules are visible. Ground-glass opacity is also present
on the left side, and a single cyst is visible in the left lower lobe (black arrow).
      Lymphoid interstitial pneumonia
• It can have both centrilobular and
  perilymphatic nodules.
• Cyst s are present.
• Ground glassing will be seen.
Miliary TB post primary.
                     Hypersensitivity pneumonitis




HRCT through the upper lobes shows patchy areas of ground-glass opacity and ill-
defined nodular opacities with a centrilobular predominance, HRCT at the lung base
shows patchy ground-glass opacities. Focal areas of relative lucency represent mosaic
perfusion. The combination of patchy ground-glass opacity and areas of lucency is
termed the headcheese sign and is typical of hypersensitivity pneumonitis.

				
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posted:4/28/2011
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