Fig. 16.2 Smooth interlobular septal thickening associated with overhydration interstitial pulmonary edema in a 59-year-old man who has mantle cell lymphoma. Patient received hydration before chemotherapy. (a, b) Lung window of CT scans (2.5-mm section thickness) obtained at levels of azygos arch (a) and lower lobar bronchi (b),

respectively, shows diffuse ground-glass opacity with smooth interlobular septal thickening (arrows) in both lungs, particularly in the anterior lungs. Also note bilateral pleural effusions (open arrows in b), small in amount. Lung lesions disappeared with diuretic therapy

Fig. 16.3 Niemann–Pick disease (lipid storage disease) in a 39-year- old woman. Targeted view of the right lung at level of the liver dome shows thickened interlobular septa (arrows) along with thickened intralobular lines (arrowhead). Also note background ground-glass opacity in lung parenchyma

CT Findings

TSCT demonstrates patchy bilateral areas of GGO, smooth thickening of the interlobular septa, and smooth intralobular lines [2, 10] (Fig. 16.3). The abnormalities may be diffuse but tend to involve mainly the lower lung zones.

Hepatosplenomegaly and peripheral lymph node enlargement are common.

CT-Pathology Comparisons

Pathologically, aggregates of large foamy cells (NP cell) are present in the parenchyma of many organs [11]. Areas of GGO on CT are related to the partial filling of the alveoli with NP cells and diffuse endogenous lipid pneumonia, and interlobular septal thickening is related to the accumulation of NP cells in the interlobular septa [2].

Patient Prognosis

Various therapeutic approaches, including enzyme replacement therapy, gene therapy, and stem cell transplantation, have been tried for this disorder. Neurodegeneration in patients with NPA proceeds rapidly and leads to death within 3 years, while those with NPB have little or no neurodegeneration and frequently survive into adulthood.

Nodular Septal Thickening

Definition

Interlobular septa are the sheetlike structures of 10–20-mm length that form the border of the secondary pulmonary lobules. The septa are usually perpendicular to the pleura in the lung periphery. They are composed of connective tissue and contain lymphatics and pulmonary venules. Nodular

thickening of the interlobular septa may be caused by the disease involving the lymphatics within the septa (Figs. 16.4, 16.5, and 16.6).

In amyloidosis, the lesions usually show lower lung zone predominance.

Diseases Causing the Pattern

The diseases causing nodular interlobular septal thickening include pulmonary lymphangitic carcinomatosis (PLC) [4] (Figs. 16.4 and 16.5) and pulmonary sarcoidosis [12] (Fig. 16.6). In silicosis and amyloidosis, nodular interlobular septal thickening may be occasionally associated [13, 14] (please also note section “Small Nodules with Perilymphatic Distribution” in Chap. 18).

Distribution

In most diseases, lung abnormalities show random or patchy and extensive distribution. In PLC, distribution may be unilateral or bilateral, focal or diffuse, and symmetric or asymmetric. In silicosis, the lesions show typically upper and middle lung zone predominance as in sarcoidosis. However, in sarcoidosis, the abnormalities may involve the whole lung without zonal predominance.

Clinical Considerations

The most common primary cancer sites related to PLC are the breasts, lungs, colon, and the stomach [4]. The presence of occupational exposure history to coal dusts or silica renders a diagnosis of pneumoconiosis. Patients with pulmonary sarcoidosis usually have no specific symptoms. The disease may be suspected with abnormal chest radiographs. Conversely patients with pulmonary sarcoidosis may have fatigue, fever, weight loss, dry cough, or shortness of breath. Up to 20 % of individuals with sarcoidosis develop skin problems such as rash or nodules. Eye symptoms such as blurred vision, pain, and photosensitivity may occur occasionally in sarcoidosis. Amyloidosis is a heterogeneous group of disorder characterized by accumulation of B-pleated sheets of insoluble proteins (amyloid). The deposition of amyloid in the lung is common in systemic amyloidosis, either in primary systemic disease or secondary to systemic disease processes such as chronic renal failure, chronic infections, rheumatoid arthritis, tuberculosis, syphilis, osteomyelitis, or inflammatory bowel disease [2].