Examqo › Examqo library › Radiology › Chest and cardiac · IMLE

HRCT patterns of lung disease

On HRCT, identify the pattern (reticular, ground glass, nodules, cysts, mosaic) and its distribution (upper or lower, central or peripheral, and within the secondary lobule) — and the combination of the two narrows the differential diagnosis.

לקריאה בעברית

Why it matters in the exam

HRCT uses thin sections (about 1 mm) with a sharp kernel, sometimes prone and in expiration. UIP pattern: subpleural basal reticulation, honeycombing and traction bronchiectasis — in an older patient with no other cause this is enough to diagnose IPF without biopsy. NSIP: basal ground glass and reticulation with subpleural sparing and little or no honeycombing — common in connective tissue disease. Chronic HP: upper or mid-zone involvement, centrilobular nodules and mosaic areas with air trapping on expiration.

Nodule distribution: perilymphatic — along the fissures, pleura and bronchovascular bundles — in sarcoidosis, silicosis and lymphangitic carcinomatosis; centrilobular — away from the pleura — in HP, RB-ILD and infectious bronchiolitis ("tree-in-bud"); random — in miliary tuberculosis and haematogenous metastases. Upper-zone diseases: sarcoidosis, silicosis with progressive massive fibrosis (masses that migrate toward the hilum, with eggshell-calcified lymph nodes), LCH, tuberculosis and ABPA. Lower-zone diseases: IPF, NSIP, asbestosis, scleroderma and aspiration. Smoking-related diseases: RB-ILD, DIP, LCH (upper nodules and cysts sparing the angles) and emphysema; sarcoidosis and HP are actually less common in smokers.

Pointing findings: "crazy paving" (ground glass with septal thickening) is classic for PAP but not specific; diffuse thin-walled cysts in a young woman — LAM; cysts with ground glass in Sjögren — LIP; central upper-zone bronchiectasis with mucus plugs — ABPA; the main sign of bronchiectasis — a bronchus wider than its adjacent artery and lack of tapering toward the periphery. In invasive aspergillosis in a neutropenic patient — a nodule with a ground-glass "halo", and later an "air crescent". An incidental solid nodule of 6–8 mm at low risk: CT at 6–12 months; above 8 mm: consider CT at 3 months, PET-CT or biopsy; below 6 mm at low risk: no follow-up needed (Fleischner 2017).

Key points

• UIP — bases, subpleural, honeycombing.
• NSIP — ground glass with subpleural sparing.
• Perilymphatic — sarcoidosis; centrilobular — HP.
• Upper zones: sarcoidosis, silicosis, LCH, tuberculosis.
• Nodule 6–8 mm at low risk — CT at 6–12 months.

Summary table

A free exam question

In the full version for subscribers

• A simple algorithm
• Memory aid
• Exam traps
• 5 review cards
• Enough for IMLE

The full version is open to subscribers of: Diagnostic radiology, Medical licensing exam (IMLE), Internal medicine.

Subscriber? Read the full topic Plans and prices 25 free questions

Sources

• Fleischner Society White Paper: Diagnostic criteria for idiopathic pulmonary fibrosis, 2018 — HRCT patterns
• ATS/ERS/JRS/ALAT Clinical Practice Guideline: Idiopathic Pulmonary Fibrosis (an update) and Progressive Pulmonary Fibrosis, 2022 — Radiological UIP patterns
• Fleischner Society Guidelines for Management of Incidental Pulmonary Nodules Detected on CT, 2017 — Solid nodule recommendations

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.