Langerhans Cell Histiocytosis

to a greater percentage of tumors occurring in the periphery of the lung with 53 % in one study [18]. The borders of the nodule are often irregular or lobulated. Approximately 10 % of SCCs show cavitation. The cavities are usually thick walled and have a nodular inner surface. Discordance between the inner and outer walls of a cavitary lesion (e.g., smooth inner walls and uneven outer walls or uneven outer and inner walls and discordant uneven sectors) is more common in peripheral lung cancer cavity and concordance between the walls (e.g., smooth inner and outer walls or uneven outer and inner walls and concordant uneven sectors) is more common in single pulmonary tuberculous cavity. Thus, the characterization of a cavitary lesion according to its cavitary internal and external walls on CT is valuable in differentiating between peripheral lung cancer cavity and single pulmonary tuberculous thick-walled cavity [9].

CT-Pathology Comparisons

dilatation of involved airways and eosinophils is commonly seen (Fig. 12.2). In late Þbrotic phase, Langerhans cells are diminished and replaced by Þbrous tissue [6].

Symptoms and Signs

Clinical presentation of pulmonary LCH is variable [19]. Despite diffuse lung involvement, symptoms can be minor or absent. Initially patients often attribute their symptoms to smoking. Dry cough and dyspnea on exertion are present in approximately two-thirds of the patients. Spontaneous pneumothorax responsible for chest pain occurs in up to 20 %. Bone lesions (<20 %), diabetes insipidus with polyuria and polydipsia (5 %), and skin lesions are the most common extrapulmonary manifestations.

CT Findings

In SCC, necrosis of the central portion of the tumor is common, especially in larger ones. Possibly because of their intimate association with proximal airways, the necrotic material can drain relatively easily and cavity formation is common. Occasionally, a cavity results from infection and abscess formation in an area of obstructive pneumonitis. Nodular inner surface of cavity is probably related to local differences in necrosis and growth rate within the tumor.

Patient Prognosis

Surgical resection is a potentially curative treatment of the early stage of SCC of the lung, with a 5-year survival rate up to 70 %. Combined modality therapy with surgery, radiotherapy, and chemotherapy can improve the survival in the patients with stages II and III. Clinical trials with novel targeted agents for advanced stage lung cancer are ongoing. Prognosis is poor (5-year survival 1 %) in the stage IV group.

Langerhans Cell Histiocytosis

Pathology and Pathogenesis

Langerhans cell histiocytosis (LCH) is a rare interstitial lung disease caused by proliferation of Langerhans cells. It can either be limited to the lung (pulmonary LCH) or be part of a systemic LCH. Langerhans cells are characterized by large, folded nuclei, vesicular chromatin, and abundantly pale to eosinophilic cytoplasm. LCH can be divided into two phases: early cellular (proliferative) and late Þbrotic phases. Early cellular phase is characterized by nodular proliferation of Langerhans cells centered on small airways, such as terminal bronchioles, and cystic

The incidence of these Þndings depends on the stage of disease. The most common thin-section CT Þndings of early LCH are multiple poorly deÞned small nodules with a centrilobular distribution [20, 21] (Fig. 12.2). Nodules measure 1Ð5 mm in diameter, although larger nodules are seen in approximately 30 % of cases. Their margins may be smooth or irregular. Larger nodules may show lucent centers. As the disease progresses, the nodules tend to cavitate, and a combination of cysts and nodules is characteristic (Fig. 12.2). Cysts are often seen in association with nodules but may be the only HRCT Þnding. They range from a few millimeters to several centimeters in diameter and may be round or irregular in shape. Regardless of the stage, the abnormalities are most severe in the upper and mid-lung zones; the lung bases are relatively spared (Fig. 12.2). Less common Þndings include reticular pattern, interlobular septal thickening, large bullae, and ground-glass opacity. The radiologic abnormalities may regress, resolve completely, become stable, or progress to advanced cystic changes. According to a study, more than half of patients show improvement on follow-up CT scans because even thin-walled cysts harbor active inßammatory cells in their walls and show improvement with treatment [6]. Spontaneous pneumothorax is seen in approximately 10 % of patients.

CT-Pathology Comparisons

LCH is histopathologically characterized by peribronchiolar proliferation and inÞltration of Langerhans cells that form stellate nodules. With progression, cellular nodules are transformed into cavitary nodules or thin-walled cysts (Fig. 12.2). In advanced stages, Þbrotic scars are surrounded by enlarged and distorted air spaces. Centrilobular nodules seen on HRCT correspond histopathologically to the area of peribronchiolar granulomas composed of Langerhans cell, eosino-