A 58-year-old Indian male with a 10-year history of progressive dyspnea undergoes HRCT chest for suspected interstitial lung disease. The scan shows bilateral basal and subpleural reticulation with honeycombing and traction bronchiectasis. The structure marked **B** in the diagram (interlobular septum) is thickened irregularly throughout both lower lobes. Which of the following HRCT patterns best explains the irregular thickening of the structure marked **B** and is diagnostic of the underlying condition?