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Q1: Describe the findings on radiography and computed tomography
The plain radiograph and computed tomogram of the chest (see p 543) demonstrated considerable reduction in the volume of her right lung with hyperlucency, a paucity of vascular markings on that side, and mediastinal shift to the right, suggesting a possible diagnosis of Swyer-James-MacLeod syndrome (a rare disease with unilateral hyperlucent lung due to bronchiolitis obliterans and pulmonary artery hypoplasia, which generally develops after lower respiratory tract infection during early childhood).
Q2: Describe the findings on bronchoscopy
Bronchoscopy (see p 543) revealed a pigmented tumour causing almost complete obstruction of the right main stem bronchus at the level of the carina.
Q3: What is the most likely diagnosis?
The most likely diagnosis is a benign pigmented lung tumour, or a melanocytic carcinoid tumour. The age of the patient, her general wellbeing and health apart from wheeze on exertion, and never having smoked, make a malignant tumour unlikely.
Q4: How would you manage this patient?
The most appropriate management is surgical excision, in view of the symptoms of progressive wheeze on exertion, and to prevent complete obstruction of the bronchus.
In our patient, a surgical opinion was sought, and a right upper lobectomy with sleeve resection of the right main stem bronchus and carina, with carinal reconstruction by tracheobronchial anastomosis was performed. Light microscopy disclosed a tumour composed of polygonal cells with clear and abundant cytoplasm. The cytoplasm contained abundant periodic acid-Schiff positive material which was digested by diastase, indicative of glycogen granules. An extensive immunohistochemical panel was applied to the tumour, which revealed positivity to HMB-45 (a marker of melanocytic lineage). Histology was consistent with a nodular clear cell tumour, with prominent melanin pigment deposition and a very low mitotic index. Abdominal ultrasonography revealed no evidence of a primary intra-abdominal tumour. On review three months later in the outpatient clinic, the patient was in excellent health, and pulmonary function tests had normalised, with an FEV1 of 2.39 l/min (95% of predicted value), and FVC of 2.68 l/min (91% of predicted value). The patient was now off all inhaled therapy, and her wheeze on exertion had resolved.
Benign clear cell tumour (BCCT) or “sugar tumour” of the lung is an unusual primary tumour originally described in 1963 by Liebow and Castleman.1 Since this time more than 40 cases of BCCT of the lung have been published worldwide, but there is only one prior report on the occurrence of a BCCT in the conducting airways.2 The presence of immense quantities of intracytoplasmic glycogen is a distinguishing feature, responsible for the name “sugar” tumour. Patients with BCCT of the lung are usually asymptomatic, and tumours are most often peripheral coin lesions discovered incidentally on routine chest radiographs.3 There is a slight female predominance among the patients, ranging from 8 to 67 years of age (median 57).3
BCCT has been thought to originate from smooth muscle cells, pericytes or neuroendocrine cells including melanocytes, although the origin of BCCT has not been clearly defined. Recent reappraisal of the entity came from the discovery of HMB-45 positivity in sugar tumour cells, suggesting an histiogenic relation with other non-melanocytic lesions known to express HMB-45, including lymphangioleiomyomatosis and angiomyolipoma, which are leiomyocytic or perivascular myofibroblastic proliferation.4 Recognition of “sugar tumour” of the lung is clinically important, as the histology of this benign tumour closely resembles pulmonary clear cell carcinoma, and also the clear cell pattern of renal cell carcinoma metastatic to the lung. However, only the BCCT demonstrates abundant intracytoplasmic glycogen, HMB-45 positivity, and negative staining for epithelial markers such as cytokeratin, epithelial membrane antigen, chromogranin, and usually S-100 protein.5 Therefore, BCCT of the lung can be distinguished from pulmonary clear cell carcinoma on the basis of electron microscopy and immunohistochemistry. Renal cell carcinoma should further be excluded by ultrasonography or abdominal computed tomography. Although slow growth is a characteristic feature of BCCT of the lung, a case report described a tumour that doubled its diameter within 21 months.6 Furthermore, while BCCT of the lung has traditionally been considered benign, a 1988 report described the case of a patient who died from metastatic BCCT of the lung.7 This fatal case indicates that benign behaviour of this tumour is not invariable.
Benign clear cell tumour (“sugar tumour”).
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