Mediastinal Paraganglioma

Clinical History

A 48 years old man without any relevant pathological history except for mild hypertension and hypercholesterolemia, on December 2006 was admitted to the emergency department for chest pain, tachycardia and moderate hypertension (160/90 mmHg). ECG showed atrial fibrillation with 130 bpm.

Imaging Findings

Cardiac MRI was then performed in order to characterize the unexpected finding (Fig. 2). Cardiac CT scan was accomplished one month later to better define the relationship of the mass with coronary vessels and monitor its potential growth (Fig. 3).
Fig. 1: Echocardiography showed normal ventricular morphology and function, and mild mitral valve prolapse; a mass with hyperechoic tissue was detected at the level of mitro-aortic junction
(arrow in Fig. 1).
Fig. 2: MRI shows a round, well defined 4 cm mass localized in epicardial fat among left ventricular outflow tract (LVOT), right ventricular outflow tract (RVOT), left coronary artery (LCA), pulmonary artery (PA), aortic root and left cardiac chambers. The lesion appeared isointense-to-heterogeneous on T1 weighted sequences, very bright on T2 weighted with fat suppression sequences and showed low contrast enhancement on perfusion (FGRET) sequences. No pericardial or pleural effusion was observed.
Fig. 3: CT scan confirmed the presence of the mass (white arrows), characterized by low-to-mid tissue density (mean value 40-50 UH) and low contrast enhancement. No signs of local invasivity, especially about coronary arteries (completely surrounded by the lesion, red arrows), aortic root and pulmonary trunk. No dimensional growth was note, neither pericardial/pleural effusion or mediastinal lymph nodes.
Differential diagnoses include Paracardiac Cyst, Coronary Aneurysm, Mediastinal Lymphoma, Mediastinal Paraganglioma and Cardiac Lipoma.

Discussion

The lesion described here is a rare case of mediastinal, paracardiac hyposecreting paraganglioma. Differential diagnosis includes a paracardiac cyst, which usually presents with dark signal on MR T1 weighted sequences and very low density (0-30 HU) on CT scan, with no contrast enhancement.
Also coronary aneurysm is not supported by evidence: The mass involves both, the anterior descending and circumflex artery, as well as the left main. Furthermore, shape, borders and size of coronary arteries are normal.
Mediastinal lymphoma looks like the above mentioned lesion, but some features are different: Lymphoma affects immunocompromised patients, generally involves the right atrium and is frequently associated with pericardial effusion. At CT, lymphoma is quite bright on un-enhanced scans, is usually locally invasive and mediastinal lymphadenopathy is often seen.
Finally, this lesion does not have the characteristics of cardiac lipoma, which has low signal on fat suppression sequences and low density (fat usually presents negative HU values) on CT scan.
Mediastinal, paracardiac paraganglioma typically affects young adults and involves the left atrium, coronary arteries or aortic root. The lesion is frequently associated with cathecholamine syndrome and has a hyperechoic signal. On MRI there is a hypo-isointensity signal on T1 weighted sequences and bright signal on T2 weighted sequences. The density on CT scan is low and normally contrast enhancement is strong, but it depends on vascularization and secerning activity. The patient is just mild symptomatic and hypertension is only moderate. This feature, together with low contrast enhancement (poor vascularization), support the hypothesis of an hyposecerning type.
The usefulness of CT or MRI scans in localizing extraadrenal catecholamine-producing tumors as cardiac paragangliomas has been showed in this case. Given their noninvasive nature and wide availability, either imaging technique represent a reasonable first step in the localization procedure, although MRI may be preferred. In this case, indeed, Multidetector CT was performed as a complement of MRI, just to emphasize anatomic details of coronary artery involvement.
Additional “second step” imaging procedures are generally required, including iodine-131 or, better, 123 metaiodobenzylguanidine (MIBG, a norepinephrine analogue) radionuclide scintigraphy scanning.
MIBG scintigraphy, a functional rather than topographic test that allows scanning of the entire body, is now considered the gold standard for localization of small adrenal lesions or extraadrenal tumors including cardiac paraganglioma. However, the high specificity of up to 100% of MIBG scintigraphy has to be balanced against its relatively low sensitivity (78%), expecially in case of low-secreting tumors: The radioisotope 123MIBG, indeed, accumulates preferentially in these tumours in proportion with catecholamine synthesis.
In this case MIBG study correctly located and confirmed the presence of an hyposecreting paraganglioma (low MIBG enhancement).
Because the tumor generally tends to engulf the coronary arteries (as in this case), surgical resection is often difficult and several deaths have been reported from intraoperative or postoperative hemorrhage.
The patient refused surgical treatment because of his good clinical conditions (actual absence of cathecholamine syndrome) versus complexity of the surgical approach.
A MR study performed one year after diagnosis didn’t show any change in morphology, dimension and signal.

Differential Diagnosis List

Final Diagnosis

Mediastinal Paraganglioma

URL:	https://www.eurorad.org/case/7470
DOI:	10.1594/EURORAD/CASE.7470
ISSN:	1563-4086