Primary Hemangiopericytoma Arising in Extralobar Pulmonary Sequestration: A Coincidence or Two Rare Disorders?

Discussion

The term HPC was initially suggested by Stout and Murray in 1942 to describe a rare tumor of vascular origin, mainly composed of capillary pericytes (1). Primary pulmonary localization of this type of neoplasm is extremely rare, can occur at any age and may have malignant potential. Benign or malignant differential diagnosis is almost impossible to establish on the basis of clinical examination or plain chest x-rays. Among 36 cases reported in the literature until 1979 (2, 3) and a subsequent case series of 18 patients (4), approximately 40% to 50% of patients with pulmonary HPC were asymptomatic at presentation, despite the impressively large size (≥5 cm) of the tumor in up to two-thirds of cases. Non-specific symptoms such as hemoptysis and chest pain were the commonest, while dyspnea or cough were less frequently met. Large-sized, homogenous, soft-tissue masses with round or slightly lobulated margins and infrequent calcification or no sign of atelectasis were characteristic, though not pathognomonic, radiographic features on x-ray (2, 3). In later studies, CT scan more accurately described calcification in 10% of cases and recognized large central areas of low attenuation in large HPCs, as a radiological indicator of malignancy (5).

Pulmonary sequestration accounts for 0.15-6.4% of all congenital pulmonary anomalies (6). EPS comprises 25% of sequestrations (7). Most cases (approximately 80%) of EPS lie between the lower lobe and the diaphragm, are left-sided and occupy the region of the posterior basal segments (6). The characteristic position of the lesion and recurrent lung infections without significant radiographic resolution in childhood or young adulthood makes intrapulmonary sequestration a possible diagnosis. On the contrary, EPS due to lack of communication with the tracheobronchial tree may remain asymptomatic for many years or less frequently present in the neonatal period with more intense clinical manifestations such as respiratory failure, cyanosis, infections and/or recurrent pulmonary hemorrhage (8). Contrast-enhanced helical CT scanning with 3-dimensional reconstruction can confirm the suspected diagnosis (9). Conventional or CT arteriography is helpful in differentiating the lesion from other abnormalities of the lung, such as pulmonary arteriovenous fistula, based on the demonstration of systemic arterial blood supply of sequestration (10). Despite the lack of a history of susceptibility to pulmonary infections in our elderly patient, the presence of a well-circumscribed mass located in the lower lung field determined our decision to proceed to CT arteriography and 3-dimensional reconstruction imaging.

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Figure 3.

Histological examination of the solid soft-tissue mass resected from the right lower lung lobe. The tumor had a perivascular hemangio-pericytomatoid pattern of cellular growth, and vessel dilatation was also observed in eosin-hematoxylin images (100×) (A). Tumor cells were strongly and diffusely positive for vimentin (B), CD34 (C): and CD99 (D) (200×).

The therapy for pulmonary sequestrations is controversial. If asymptomatic, they are often left alone. Even though EPS may show spontaneous regression, the latest study suggests that the volume and diameter of systemic feeding arteries of EPS spontaneously decreased within 4 years without treatment in neonatal patients (11). For those patients with recurrent infections or other symptoms, surgery or embolization or both have been recommended (12). Although the incidence of carcinoma is low, its existence has provided an argument for the need for surgery (13).

The occurrence of benign or malignant neoplasms within pulmonary sequestrations is extremely rare. Nine other cases of primary lung cancer (mainly adenocarcinoma or squamous carcinoma) have already been reported in the English literature. The tumor was found to arise within an intralobar sequestration in all but one case (14). Therefore, the etiology of the carcinomas in the sequestration cases may be multifactorial and may include chronic inflammation and irritation.

There is a single published case of vascular tumor, sclerosing hemangioma, arising within an EPS in a young child (15). A more recent study of a small series of surgically removed intra- and extrapulmonary sequestrations, revealed hypertensive vascular changes and a possible mechanism of exposure to the elevated pressures of systemic arterial supply was implied (16). Although developmental abnormalities and chronic vascular changes within pulmonary tissue may have a pathogenetic role, this extremely rare case of HPC development in EPS might be considered a coincidental association.

Radical surgical excision is the treatment of choice for HPC. Intraoperative and postoperative radiotherapy has been proposed as an innovative approach after complete tumor resection (17). The benefits of radiotherapy as palliative treatment for local recurrence or superior vena cava obstruction or chemotherapy for treating patients with metastatic disease or those for whom surgery is not feasible have not yet been clarified (3). Long-term postoperative observation is highly recommended (5), since primary pulmonary HPC may recur locally (pleura, lung, mediastinum) or distally in up to one-third of cases, usually within the first 1-2 years but rarely more than a decade after surgical excision of the tumor (4, 18).