Peripheral wedge-shaped radiographic lung opacity in a young patient

A 19-year-old female presented with right-sided chest pain, non-productive cough and dyspnea since 1 week. There was no history of fever, hemoptysis and anorexia or weight loss. A chest radiograph and, subsequently, a computed tomography (CT) scan were performed. Laboratory investigations were normal except for microcytic hypochromic anemia with Hb of 8 g/dL. Histopathology provided the final diagnosis.

QUESTIONS

1. What is the abnormality on chest radiograph and what is the differential diagnosis?

2. What are the findings on CT scan?

3. What is the most likely diagnosis on CT scan?

4. What is the histological characteristic of the chest lesion?

ANSWERS

The chest radiograph shows a peripheral wedge-shaped opacity in the right lower zone [Figure 1]. The differential diagnosis includes-

Figure 1.

Chest radiograph in the posteroanterior projection

1. Vascular wedges – pulmonary infarct, invasive aspergillosis Bronchial wedges – consolidation, atelectasis

2. An enhancing mass lesion arising from the right postero–lateral chest wall with a larger intrathroracic and a smaller extrathoracic component [Figure 2a]. The mass lesion is wedge shaped with a broad base toward the chest wall [Figure 2b]. Periosteal reaction is seen along the right 8^th rib, which was encased by the mass [Figure 2b].

3. A neoplastic lesion arising from the chest wall. Considering the patient's age and site of the lesion, the most likely diagnosis is primitive neuroectodermal tumor (PNET) of the chest wall.

4. Monotonous small round cells that stain dark blue with hematoxylin and eosin.

Figure 2.

(a) Contrast-enhanced computed tomography (CT) chest axial image in the mediastinal window setting and (b) CT chest sagittal image in the bone window setting

DISCUSSION

Considering the relatively short duration of symptomology, absence of signs of infection and the radiographic appearance, initially, a pulmonary infarct (Hampton's hump) due to thromboembolism was suspected in our patient. Further evaluation with CT scan however revealed a wedge-shaped mass lesion arising from the chest wall. Histopathology of the biopsied tissue confirmed the lesion to be a PNET.

Malignant round cell tumors are a group of aggressive malignancies with similar histopathological features. Some of the tumors that belong to this group are Ewing's sarcoma (ES), PNET, rhabdomyosarcoma, lymphoma and neuroblastoma.[1] PNET and ES share same chromosomal translocations. PNET commonly affects children and young adults in the first three decades of life. It commonly affects the central nervous system and rarely involves the peripheral sites. The chest wall is the most common peripheral site for PNET, where it is also known as Askin's tumor.[2] Thus, another “wedge” that should be considered in the differential diagnosis of wedge-shaped peripheral lung opacity in young patients is the neoplastic wedge of Askin's tumor.