Multinodular Disease: Study

The most important differential diagnoses for this pattern of disease are silicosis and coal worker pneumoconiosis. In both of these occupational diseases, perilymphatic nodules are the primary abnormality, typically involving the mid and upper lung fields. While these entities may simulate the appearance of sarcoidosis, they are usually easily diagnosed when correlated with clinical history. This includes other rare occupational lung disease, for example, siderosis, that may also simulate the appearance of sarcoidosis.
While lymphangitic carcinomatosis may result in perilymphatic nodules, in fact, CT scan findings are most often characterized by markedly thickened nodular interlobular septae usually asymmetrically involving the lower lobes and usually associated with adenopathy and effusions. Nodules, when present, tend more often to be well-defined and are often associated with discrete feeding vessels, further identifying them as hematogenous in origin. Lym-phangitic carcinomatosis rarely mimics findings that are characteristic of sarcoidosis.
If nodules prove to be diffuse instead of clustered, they are properly considered to be random in distribution (Table 1). By definition, true random distribution will lead to nodules being identified along pleural and fissural surfaces as well as along the axial interstitium. However, in distinction from primarily perilymphatic disease, random nodules may also be identified in even greater numbers when dispersed randomly throughout the lungs,

Included in this category most importantly are hematogenous metastases. Unlike nodules in patients with sarcoidosis, metastatic nodules tend to be smooth, well-defined lesions (Fig 8, 9). However, a wide variety of morphologic appearances has been noted. In a study comparing the HRCT scan features of pulmonary metastatic lesions with autopsy findings, while nodules most often proved to have well-defined margins (38% of cases), nodules with well-defined irregular margins, poorly defined smooth margins, and poorly defined irregular margins could be identified in 16%, 16%, and 30% of cases, respectively. While nodules range from a few millimeters to > 1 cm, they are frequently similar in size.


Figure 8. Random nodules: hematogenous metastases. An HRCT scan of a 1-mm section through the lower lobes shows innumerable sharply defined nodules throughout both lungs. Note that while many of these lie along pleural and fissural surfaces, or less commonly appear related to adjacent vessels (arrows), most are unattached to adjacent structures. When sufficiently well defined and generally uniform in size, this pattern of diffuse nodularity is easily separable from that resulting from perilymphatic disease.


Figure 9. Random nodules: metastatic thyroid cancer. An HRCT scan of a 1-mm section through the mid-thorax shows innumerable small nodules. Note that, in addition to unattached nodules, many of these lie along both the minor and right major fissures (arrows), as well as along the proximal middle lobe pulmonary artery (arrowheads). Although there are fewer nodules than shown in Figure 8, in the appropriate clinical stetting this pattern is again consistent with metastatic disease.

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