The most likely diagnosis is: b) a persistent left SVC

Upon further review of the coronal enhanced CT image (Figure 2), it’s evident that the opacified (bright white) left subclavian vein (from the left antecubital contrast injection) drains directly into the vertical vascular structure, identified with arrows on Figure 2. The right superior vena cava (SVC), marked on that image as well, does not contain contrast, as it’s not connected to the left-sided upper body venous structures, the way it normally would be. The left-sided vertical vascular structure corresponds to a persistent left-sided SVC, which drains into the coronary sinus through an anomalous congenital connection, back to the right side of the heart. The anomaly is unrelated to the patient’s presentation and is purely an incidental finding.

A persistent left-sided SVC (PLSVC) results from lack of involution of the embryologic remnant vascular structure present in the developing fetus. It’s present in 0.3% of the population. With this anomaly the left brachiocephalic vein doesn’t fully develop and as a result the left upper extremity and the left side of the head and neck drain into the right atrium via the PLSVC, typically through the coronary sinus. This venous anatomical anomaly, on its own, is considered benign and is often discovered incidentally, as in the case presented. However, the anomaly can also be associated with congenital heart defects (including ventricular septal defect [VSD], atrio VSD) that can be associated with significant morbidity and mortality.

During detailed obstetrical ultrasound scanning, the discovery of a PLSVC should prompt a thorough search of the fetus for more cardiac, and extracardiac, abnormalities. Referral for a specific fetal echocardiography study would be reasonable in such a case.

A Pancoast tumour is the term given to describe a primary bronchogenic carcinoma that develops in the apical pleuropulmonary groove (lung apex). These tumours often involve local invasion into adjacent thoracic inlet structures, including the brachial plexus. The primary tumour type could be adenocarcinoma, squamous cell or large cell but almost never small cell carcinoma. The lesion typically produces a local irregular mass appearance and shouldn’t be considered in the case presented.

Pulmonary AVMs can be solitary or multiple (as seen in Osler-Weber-Rendu disease or hereditary hemorrhagic telangiectasia). These lesions typically produce a local lobulated mass lesion with definable tortuous vessels (arterial and venous) entering and exiting the structure. Although a consideration in this case, the direct connection to the enhanced left-sided venous structures of the PLCVS with non-opacification of the right SVC provides the real diagnosis.

Some lung metastases can be quite vascular with increased chance of secondary pulmonary hemorrhage, from primaries such as melanoma, choriocarcinoma, renal cell carcinoma and certain sarcomas. These vascular metastases are typically multiple, with quite irregular margination (due to local hemorrhage), and increased density on enhanced CT scans (due to vascularity). This diagnosis shouldn’t be seriously considered in this case.

Castleman’s disease (benign angiofollicular hyperplasia) describes a usually benign disorder of the lymph nodes, typically involving the mediastinum region. The nodes are characteristically bulky and hypervascular, and as such are seen as brighter than normal mediastinal nodes on enhanced CT. Occasionally, the condition can become more widespread in the body and run a more aggressive course, progressing to non-Hodgkin’s lymphoma (or as some have termed it, ‘Castleman’s lymphoma’), thus requiring systemic therapy. Although this diagnosis might have been considered on the axial image alone, the elongated appearance of the highlighted abnormality (the PLSVC) on the coronal CT image would rule it out.

References:

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