|CASE IN POINT: CLINICS IN RADIOLOGY
|Year : 2015 | Volume
| Issue : 3 | Page : 141-144
An unusual cause of scimitar sign: Anomalous unilateral single right pulmonary vein associated with accessory liver lobe
Pragya Singh, Mahesh Kumar Mittal
Department of Radiodiagnosis and Imaging, Vardhman Mahavir Medical College, Safdarjung Hospital, New Delhi, India
|Date of Web Publication||2-May-2016|
Flat No. 903, Trimurti Heights, Sector 39, Gurgaon - 110 019, Haryana
Source of Support: None, Conflict of Interest: None
We report a case of an anomalous unilateral single right pulmonary vein resembling a scimitar sign on chest X-ray. Only a few cases have been reported in the literature describing this interesting rare anomaly that is often confused with arteriovenous malformation and hypogenetic lung syndrome (scimitar syndrome). This report briefly discusses the embryology of the pulmonary veins, classification of the pulmonary venous anomalies, and various causes of scimitar sign.
Keywords: Left atrium, pulmonary vein, scimitar sign
|How to cite this article:|
Singh P, Mittal MK. An unusual cause of scimitar sign: Anomalous unilateral single right pulmonary vein associated with accessory liver lobe. Astrocyte 2015;2:141-4
|How to cite this URL:|
Singh P, Mittal MK. An unusual cause of scimitar sign: Anomalous unilateral single right pulmonary vein associated with accessory liver lobe. Astrocyte [serial online] 2015 [cited 2020 Nov 27];2:141-4. Available from: http://www.astrocyte.in/text.asp?2015/2/3/141/181515
| Introduction|| |
The “scimitar sign” on plain chest radiograph is commonly attributed to the presence of a scimitar vein, which is a variant of partial anomalous pulmonary venous drainage. Scimitar syndrome was usually a plain X-ray diagnosis with no differential diagnosis. However, with the advent of multidetector computed tomography (CT), many other conditions are detected which resemble scimitar syndrome on plain X-ray and their management is drastically different. The various causes of scimitar sign on plain X-ray are scimitar syndrome, scimitar variant, anomalous unilateral single pulmonary vein (AUSPV), meandering pulmonary vein, pulmonary arteriovenous malformation, pulmonary varix, an anomalous intrapulmonary venous connection to superior vena cava (SVC), obstruction of a major pulmonary vein with development of distended intrapulmonary collateral, and an anomalous inferior vena cava (IVC) with normal pulmonary venous drainage.,
The normal pulmonary venous drainage is into the left atrium (LA) through superior and inferior pulmonary veins on each side. This type of drainage is found in 82% of the population. The classification of pulmonary venous anomalies is described as anomalous connections, anomalous drainage, or abnormal numbers of pulmonary veins. When one or more than one pulmonary veins connect abnormally to systemic veins instead of the LA, it is termed as anomalous pulmonary venous connection whereas in abnormal pulmonary venous drainage, pulmonary veins connect normally to the LA but drain abnormally, most commonly due to malaligned atrial septum. Both the above-mentioned conditions cause left to right shunt.
The number of pulmonary veins draining into the LA can vary from one to five. There is a wide variation in the anatomy, clinical presentation, and expected outcome of these anomalies., The most common variation of the pulmonary veins' number is the presence of a common pulmonary vein on either the right or left side with an incidence of 23.9%. The next most common variation is the increase in their numbers which is mainly observed as an additional vessel called the right middle lobe pulmonary vein with a prevalence of 1.6%.
An AUSPV is a rare anomaly, which also presents with the scimitar sign. Despite a similar radiographic appearance, they have very different prognostic implications. AUSPV is often confused with the more common scimitar syndrome as both consist of an anomalous right pulmonary vein, taking a tortuous route through the lung, resulting in a scimitar sign on chest X-ray. However in contrast to scimitar syndrome, the AUSPV terminates normally in the LA, rather than the IVC. Our case is rare as the meandering right pulmonary vein (MRPV) was the single vein draining the entire right lung and was associated with numerous other congenital anomalies of scimitar spectrum.
| Case Report|| |
A chest X-ray of 33-year-old male presented with occasional cough and dyspnea on exertion. Chest radiograph demonstrated a curvilinear tubular structure running from the right mid zone toward the right cardiophrenic recess [Figure 1], resembling a scimitar sign. In addition, there was volume loss in the right hemithorax with mediastinal shift to the right suggesting cardiac dextroposition. An anomalous pulmonary vein––such as that seen in scimitar syndrome––was suspected.
|Figure 1: Posteroanterior chest radiograph shows a curvilinear structure running from the right mid zone toward the right cardiophrenic recess (straight arrow), resembling a scimitar sign. In addition, there is volume loss in the right hemithorax with mediastinal shift to the right suggesting cardiac dextroposition. A well defined homogenous radiopacity is seen in the right paravertebral region with broadbase toward mediastinum silhouetting the right hemidiaphragm (curved arrow).|
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Contrast-enhanced CT revealed a single dilated right pulmonary vein with an aberrant tortuous route, coursing inferomedially toward the diaphragm before turning upward and draining normally into the LA [Figure 2]. There was no connection to the IVC. It also confirmed the X-ray findings of right lung hypoplasia and cardiac dextroposition. The right main pulmonary artery was smaller than the left, suggestive of mild pulmonary artery hypoplasia. In addition, the right bronchus showed left type of bronchial branching with absent bronchus intermedius. Inferior accessory fissure and azygos fissure were present with separate azygos lobe being supplied by the azygos bronchus. The medial basal segment showed anomalous systemic arterial supply from the superior aspect of celiac artery. No abnormal arteriovenous connection was seen. Focal eventration of the right hemidiaphragm was also present with focal intrathoracic herniation of accessory hepatic lobe connected with caudate lobe into the left hemithorax through the IVC hiatus [Figure 3]. Left internal jugular vein and subclavian vein were joined to form the left brachiocephalic vein, which further formed left-sided SVC draining into the right atrium. Right-sided brachiocephalic vein formed right-sided SVC draining into the right atrium. Left superior and inferior pulmonary veins were normal in morphology, course, and drainage. Heart was normal in morphology with no evidence of any congenital anomalies. No focal lung parenchymal lesion was seen.
|Figure 2: (a) Maximum intensity projection in axial reformat demonstrating the path of the anomalous pulmonary vein (white block arrows) and its connection to the left atrium. (b) Hypoplastic right pulmonary artery (curved solid arrow) and double superior vena cava (line arrows) are shown in axial maximum intensity projection. Right lung is hypoplastic with ipsilateral mediastinal shift. Coronal (c) and sagittal (d) maximum intensity projection reformats are showing the the path of the anomalous pulmonary vein (white block arrows) and its connection to the left atrium.|
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|Figure 3: (a) Coronal minimum intensity projections show the bifurcation of the right main bronchus (bilateral left type of bronchial branching). Azygos bronchus supplying azygos lobe is seen demarcated by the azygos fissure. (b) Axial computed tomographic image in lung window shows inferior accessory fissure (solid arrow). (c) Systemic supply from celiac artery (solid arrow) entering the right hemithorax through inferior vena cava hiatus and supplying the medial aspect of the right lung. There is no evidence of any sequestration. (c and d) The accessory lobe from the caudate lobe of liver herniating into the right thorax through the inferior vena cava hiatus (curved solid arrow). The herniated lobe is in posterior relation to the inferior vena cava (black line arrow).|
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| Discussion|| |
The scimitar sign describes a curved vascular shadow on a chest X-ray, which courses along the right cardiac border toward the right cardiophrenic angle. It is so-called because the appearance resembles a Turkish sword or scimitar. Scimitar syndrome is a rare pulmonary anomaly which consists of anomalous pulmonary venous drainage of the right lung to the IVC (giving rise to the scimitar sign), anomalous systemic arterial supply of the right lower lobe from either the thoracic or abdominal aorta, hypoplasia of the right lung, with resultant cardiac dextroposition and right pulmonary artery hypoplasia.
The scimitar sign was originally thought to be diagnostic of scimitar syndrome; however, a false positive scimitar sign (pseudoscimitar sign) is a rare possibility. Morgan and Forker, in 1971, described the first case in which the scimitar sign and features of scimitar syndrome were present, but the aberrant pulmonary vein ultimately drained normally into the LA. Previous case reports of scimitar sign were reviewed. Review of the literature demonstrates that 14 out of 35 cases have had associated lung hypoplasia. Our case is the sixth to date associated with a bi-lobed right lung. As per the review of literature, various causes of scimitar sign on chest X-ray are enlisted in [Table 1]. A case report of accessory hepatic lobe with coincident association with intralobar pulmonary sequestration has been described. No association between accessory hepatic lobe with scimitar sign/syndrome has been reported yet.
According to the revised classification by Rodrigues et al., MRPV to describe cases in which the anomalous vein draining part of right lung terminates normally into the LA, reserving the scimitar variant for those with a dual connection to IVC and the LA. The term “MRPV” was coined by Goodman et al. and is suggested for cases that have more than one anomalous pulmonary vein draining into the LA. AUSPV should be used to describe cases where there is a single anomalous vein draining the entire ipsilateral lung to the LA or IVC.
Scimitar syndrome, scimitar variant, AUSPV, and MRPV can be considered as a spectrum of pulmonary anomalies having a common embryological basis, with scimitar syndrome at one extreme, AUSPV at the other, and scimitar variant somewhere in between. The differential diagnosis is highlighted in [Table 2]. It is likely that the stage of embryogenesis at which the anomaly occurs determines which condition develops. For example, persistence of the primitive communications between the pulmonary and systemic vascular supplies may lead to scimitar syndrome if the connection between the right pulmonary vein and LA is obstructed, or scimitar variant if this connection is patent., Abnormally delayed obliteration of the pulmonary and systemic connections may result in a MRPV with an anomalous route in the lungs, but ultimately draining normally into the left atrium. AUSPV occurs as a consequence of atresia or hypoplasia of one of the pulmonary veins prior to pulmonary segmentation, with drainage of the entire lung subsequently occurring via the remaining vein. The frequent association of the anomaly with a hypoplastic hemithorax supports this mechanism.
Evidence that scimitar syndrome and AUSPV both represent variations within the same spectrum of anomalies lies in the fact that some additional anatomical variants are shared between both anomalies. As mentioned previously, both are frequently associated with a hypoplastic right lung and cardiac dextroposition. Anomalous systemic arterial supply to the lower right lung is classically associated with scimitar syndrome; this anomaly has also been described in two of the published cases of AUSPV as was seen in our case. Associated findings of bi-lobed right lung, accessory fissures, and intrathoracic herniation of accessory lobe of liver as seen in our case have not been described previously in case of AUSPV. Pearl  reported a small branch from the anomalous single pulmonary vein draining to the IVC. These anomalous vessels––although small in caliber and unlikely to be of great physiological significance in these cases––represent forms of AUSPV that are closest to the scimitar end of the spectrum of pulmonary venous anomalies.
| Conclusion|| |
This case highlights that the chest X-ray features of scimitar syndrome are not diagnostic and AUSPV should be considered in their presence. AUSPV has many features in common with scimitar syndrome, with both conditions likely sharing a similar pathogenesis. However, the anomaly does not require intervention. Scimitar syndrome results in a left-to-right shunt, which can lead to cyanosis and may require surgical correction. Consequently, the patients are often symptomatic and present at a young age. In contrast, there is no left-to-right shunt in AUSPV. As in this case, patients are usually asymptomatic, with the diagnosis made incidentally. Treatment has not been required in any reported case of AUSPV. Awareness of both of these uncommon anomalies, their radiographic appearance, and other frequently associated anomalies are important for the practicing clinician, to spare unnecessary investigations for those patients presenting with the scimitar sign on chest radiograph. Differentiation between these conditions is required to help decide whether treatment is necessary. Modern multislice CT technology allows clear depiction of the vascular connections and associated anatomy and has superseded invasive pulmonary angiography and cardiac catheterization as the investigation of choice for AUSPV.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]