Superior vena cava syndrome with hot quadrate lobe sign

A 69-year-old man, currently a cigar smoker, was referred to the otorhinolaryngology, especially for dysphonia and was diagnosed with right vocal cord paralysis. He presented with mild thoracic and abdominal collateral circulation, productive cough, dyspnoea and thoracic discomfort.

Complementary exams were performed to aid the diagnosis, and a CT scan highlighted the presence of a neoplastic mass with an infiltrative appearance in the right paratracheal region. The diagnosis of an adenocarcinoma was established, and the patient underwent radical chemotherapy and radiotherapy.

A revaluation enhanced CT was obtained and revealed signs of local recurrence, with a large heterogeneous mass in the right upper paramediastinum, corresponding to the region of the primary lesion, causing obstruction of the superior vena cava in its most cranial portion, sparing the portion that joins the right auricle (Figure 1). There were signs of chronicity, such as venous collaterals on the abdominal and thoracic walls, and engorgement of the azygos and hemi-azygos systems (Figures 1 and 2).

In the upper abdomen, the CT scan identifies a hypervascular area in the anterior portion of segment IVb, reflecting a change in perfusion explained by the context of obstruction of the superior vena cava (Figure 3).

Background

In superior vena cava syndrome (SVCS), CT scans may reveal enhancement of the quadrate lobe during the arterial or early portal venous phase [1]. We present a case of a paratracheal adenocarcinoma leading to SVCS and highlight the physiological cause and significance of this imaging characteristic.

The “hot spot” or “hot quadrate lobe” refers to an increased blood supply in segment IVa of the liver (also known as the quadrate lobe) [1–3]. It is occasionally observed in obstruction of the SVC and arises due to the alternative blood circulation routes between the superior vena cava and the left portal vein, through the superficial thoracoabdominal and paraumbilical veins [1–5].

Clinical Perspective

SVCS is usually caused by extrinsic compression, with thoracic malignancies accounting for over 60% of the cases [1,3,4]. Clinical manifestations include the gradual dilation of veins and oedema in the upper body, central nervous system disturbances, as well as respiratory distress due to oedema in the trachea and oesophagus [1,4]. When partial and gradual, sufficient collateral circulation may develop, leading to the absence of noticeable signs and symptoms [1,3,4].

The systemic veins can establish connections with the umbilical and paraumbilical veins through the musculophrenic and superficial epigastric veins [1]. The umbilical and paraumbilical veins tend to drain into the left branch of the portal vein, leading to the formation of a systemic portal shunt [1]. As a result, there is an increase in blood flow during the arterial phase in the specific area of the liver supplied by the left branch of the portal vein [1,2,4]. This phenomenon of systemic portal shunting, combined with the preferential drainage of the umbilical and paraumbilical veins into the left branch of the portal vein (Figure 4), constitutes the physiological foundation for the “focal hepatic hot spot” in the quadrate lobe (Figure 3) [1,2,4,5].

Imaging Perspective

CT diagnosis of SVCS requires two imaging findings:

• Decreased or absent opacification of central venous structures beyond the point of obstruction, which is typically accompanied by an obstructing lesion or an intraluminal filling defect (Figure 1) [1–5].
• The presence of opacified collateral venous channels, indicating the development of alternative pathways for blood flow (Figure 2) [1–5].

The focal hepatic “hot spot” in the quadrate lobe is characterised by a distinct region of concentrated enhancement during the arterial phase that is equal to or even greater than that of the aorta [1]. This area subsequently undergoes partial washout and appears slightly hyperdense or isodense during the venous phase [2]. The unique location, wedge shape, arterial and venous phase characteristics, as well as the presence of collateral vessels, contribute to the high specificity of this lesion as an SVCS (Figure 4) [1–5].

Take-Home Message / Teaching Points

• This sign serves as a valuable clue in diagnosing thoracic central venous obstruction.
• This sign is particularly relevant if clinically unapparent SVCS.
• This sign is highly specific for SVCS.

Written informed patient consent for publication has been obtained.