Intrathoracic carotid-body tumour (chemodectoma)

Cross-Sectional Imaging and Thoracoscopic Resection of Functional Intrathoracic Paraganglioma of the Aortic Body

Paragangliomas are extra-adrenal tumors that are derived from neuroendocrine chromaffin cells. The rare disease has a variable presentation depending upon its anatomic location and functionality. We describe the case of a 56-year-old female patient who had an incidental mass found on imaging. The patient underwent biochemical testing and a mediastinal biopsy due to the nonspecific imaging findings. The mediastinal mass was resected through hemisternotomy and found to be a functional paraganglioma. This case highlights the importance of radiologists to consider the prospect of paragangliomas in the differential diagnosis of an intra-thoracic mass.

PHD2 inactivation in Type I cells drives HIF-2α-dependent multilineage hyperplasia and the formation of paraganglioma-like carotid bodies

KEY POINTS

The carotid body is a peripheral arterial chemoreceptor that regulates ventilation in response to both acute and sustained hypoxia. Type I cells in this organ respond to low oxygen both acutely by depolarization and dense core vesicle secretion and, over the longer term, via cellular proliferation and enhanced ventilatory responses. Using lineage analysis, the present study shows that the Type I cell lineage itself proliferates and expands in response to sustained hypoxia. Inactivation of HIF-2α in Type I cells impairs the ventilatory, proliferative and cell intrinsic (dense core vesicle) responses to hypoxia. Inactivation of PHD2 in Type I cells induces multilineage hyperplasia and ultrastructural changes in dense core vesicles to form paraganglioma-like carotid bodies. These changes, similar to those observed in hypoxia, are dependent on HIF-2α. Taken together, these findings demonstrate a key role for the PHD2-HIF-2α couple in Type I cells with respect to the oxygen sensing functions of the carotid body.

ABSTRACT

The carotid body is a peripheral chemoreceptor that plays a central role in mammalian oxygen homeostasis. In response to sustained hypoxia, it manifests a rapid cellular proliferation and an associated increase in responsiveness to hypoxia. Understanding the cellular and molecular mechanisms underlying these processes is of interest both to specialized chemoreceptive functions of that organ and, potentially, to the general physiology and pathophysiology of cellular hypoxia. We have combined cell lineage tracing technology and conditionally inactivated alleles in recombinant mice to examine the role of components of the HIF hydroxylase pathway in specific cell types within the carotid body. We show that exposure to sustained hypoxia (10% oxygen) drives rapid expansion of the Type I, tyrosine hydroxylase expressing cell lineage, with little transdifferentiation to (or from) that lineage. Inactivation of a specific HIF isoform, HIF-2α, in the Type I cells was associated with a greatly reduced proliferation of Type I cells and hypoxic ventilatory responses, with ultrastructural evidence of an abnormality in the action of hypoxia on dense core secretory vesicles. We also show that inactivation of the principal HIF prolyl hydroxylase PHD2 within the Type I cell lineage is sufficient to cause multilineage expansion of the carotid body, with characteristics resembling paragangliomas. These morphological changes were dependent on the integrity of HIF-2α. These findings implicate specific components of the HIF hydroxylase pathway (PHD2 and HIF-2α) within Type I cells of the carotid body with respect to the oxygen sensing and adaptive functions of that organ.

Lessons to be learned: a case study approach. Paraganglioma of the urinary bladder

Primary paraganglioma arises infrequently in the urinary bladder. We present here the clinicopathological, immunohistochemical and ultrastructural findings in a 23-year-old Saudi female. She was hospitalised because of gross haematuria over the previous seven days. The intravenous urogram revealed a filling defect in the urinary bladder. Cystoscopy disclosed a non-papillary tumour arising from the roof of the bladder neck. Transurethral resection was, accordingly, performed--but marked fluctuation in blood pressure was observed during the procedure. The histopathological findings of trabeculae and small nests of plump oval to spindle cells with a clear to acidophilic cytoplasm, forming an organoid pattern and demonstrating inconspicuous mitotic activity, were diagnostic of paraganglioma of the urinary bladder, the diagnosis was confirmed by means of immunohistochemical and ultrastructural studies. The endocrine markers chromogranin A and neuron-specific enolase were positive in chief cells; sustentacular cells at the periphery of neoplastic cell clusters were positive for S-100 protein. Neurosecretory granules were identified by electron microscopic examination. It is emphasised that, currently, there are no anatomico-pathological criteria to distinguish benign and malignant forms of the disease. Post-surgical recovery was uneventful in this case. Recurrence and metastases, though infrequent, have been reported in the literature; therefore, radiation therapy may be an important adjunct--and long-term follow-up is mandatory.

Aortico-pulmonary paraganglioma: report of a case with ultrastructural study and review of the literature

The light microscopic and ultrastructural features of an aortico-pulmonary paraganglioma (A-PP) are presented. The tumor was characterized by organoid clustering of neoplastic chief cells to form Zellballen. Argyrophilic granules were demonstrated within chief cell cytoplasm using a modified Grimelus technique. Ultrastructurally, three distinct cell types were present within the tumor: endothelial cells, pericytes and neoplastic chief cells. Membrane-bound neurosecretory granules were present and measured 100 to 2000 nm in diameter. "Light" and "dark" chief cells were less distinct than previously reported in other head and neck paragangliomas. Analysis of the 36 documented A-PP reported in the English literature reveals that the tumor has been either incompletely excised or has been considered unresectable in one-third of the cases. The reported surgical mortality is 9%, or approximately equal to the incidence of malignant behavior. The treatment of choice is surgical resection but when this is not possible, radiation may be a useful adjunct in therapy.

Mediastinal paragangliomas (aortic body tumor): a report of four cases and a review of the literature

Four cases of paraganglioma originating in the supra-aortic or aortico-pulmonary bodies are described. A review of the reported examples of aortic body tumors and a study of these four cases indicate that there is a high incidence of aggressive tumor growth in the mediastinum, with resultant important morbidity or death in 16 of 35 cases. The morphologic features of aortic body tumors are identical to those of paragangliomas of other locations, and the occurrence of invasive growth and/or metastasis cannot be predicted on histologic grounds.

Malignant mediastinal chemodectoma

A 20-year-old man with a posterior mediastinal mass and erosion of the rib proved to have a malignant chemodectoma. The case is of interest because of the rare location and malignant fatal course.