5-3-Diffuse reticular pattern:

1-Characterized by interlacing linear shadows appearing as a mesh or a net.

2-It is a diffuse disease with predominantly reticular pattern.

3- What the referring physician needs to know:

-Chest radiograph is normal in 10% of patients with interstitial lung diseases.

-Chest radiograph is of limited value in the differential diagnosis with interstitial lung disease.

-High resolution CT is the imaging modality of choice for assessment of patients with interstitial lung disease.

-High resolution CT often allow suggestive diagnosis.

-Definitive diagnosis requires integration of clinical and CT findings and, commonly, lung biopsy.

4-Reticular pattern HR CT findings:

-Most important signs are(All interstitial diseases give the same appearance).

*Peri bronchial cuffing---Bronchial thickening.

*Septal lines.

High-resolution CT image shows 0.5 to 2 cm long lines (straight arrows) and polygonal arcades outlining one or more pulmonary lobules. These linear opacities (septal lines) reflect the presence of thickening of the interlobular septa. Also noted are prominent centrilobular dots (curved arrows) which represent thickening of the interstitium along the centrilobular bronchiole.

*Cystic abnormalities and honey combing(thickened wall to differentiate it from cystic lung diseases).  

*Traction bronchiectasis(due to bronchial traction by fibrosis).

Transverse CT scan shows traction bronchiectasis (arrows) cased by retractile pulmonary fibrosis.

-Less important signs

*Spider appearance of blood vessels.

*Interface sign---sub pleural irregularities(pathognomonic of interstitial fibrosis in early stage). 

5-Reticular pattern causes:

-Interstitial pneumonias which are the following

Remember mnemonic---A N D U for types of interstitial pneumonias which are

A---Acute interstitial pneumonia(fever,cough,peripheral lesions).

N---Non specific interstitial pneumonia.

D---Desquamative interstitial pneumonia.

U---Usual interstitial pneumonia.

-Interstitial pulmonary edema(central lesions which could be linear with patchy types of pneumonia).

-Idiopathic pulmonary fibrosis.

-Collagen vascular diseases, as systemic lupus erythromatosis, Rheumatoid arthritis and poly arteritis nodosa.

-Induced lung diseases caused by drugs such as cytotoxic drugs or irradiation(interstitial or alveolar according to type of drug).

6-When you are facing a case of reticular pattern, try first to exclude interstitial pulmonary edema by looking to the heart, to prove no cardiac enlargement, if enlargement is not seen, review symptoms and signs of interstitial pneumonia, collagen vascular diseases, searching for history of drug intake or irradiation exposure, if not, go directly to idiopathic pulmonary fibrosis.

7-Remember important rules

-Never ever you will see an isolated diffuse parenchymal lung disease of one pattern.

-Almost all cases will be demonstrated by one or two types of diffuse parenchymal patterns such as reticular pattern with cystic one or ground glass pattern and so on.

-Look to the prominent pattern in your case and use it for diagnosis.

8-There are also two other lesions causing reticular pulmonary lesion with lymphadenopathy.
These lesions are:
-Sarcoidosis. 


*90% of patients with sarcoidosis have chest changes.
*Bilateral hilar and mediastinal lymphadenopathy.
*Interstitial lung disease plus or minus lymphadenopathy.
*Alveolar pattern simulating acute inflammatory disease.
*Cavitation, atelectasis and effusion(rare).

Types of sarcoidosis:
Type1-Nodal type causing lymphadenopathy without lung affection.
Type2-Nodal + interstitial lung disease.
Type3-Alveolar lung disease without lymphadenopathy.

Clasical appearance of sarcoid lymphadenopathy
It characterized by being discrete, homogenous, containing calcium (or not) lymphadenopathy occurring in a female patient suffering from coughing(which suggests interstitial components).


-Lymphangitis carcinomatosis.

1-To diagnose lymphangitis carcinomatosis, you should have history of primary. 
2-Characterized by reticular pulmonary opacities with beading appearance.
3-Some of these opacities could coalesce together forming bigger nodules similar to that of metastases, if you find this appearance, you can diagnose lymphangitis carcinomatosis.
4-Reticular lung disease in a patient having primary malignancy, you can diagnose lymphangitis carcinomatosis.