Keywords
pulmonary artery sarcoma - sarcoma - angiosarcoma - wall eclipsing sign - PAS
Key Message
Multimodality imaging approach should be made use of in the setting of an atypical
clinical presentation to arrive at the diagnosis of pulmonary artery sarcoma and thereby
initiate prompt treatment.
Introduction
Primary pulmonary artery sarcoma (PAS) is a rare disease with poor prognosis, having
an incidence of ∼0.003%, with only close to 400 cases having been reported in literature
till date. Angiosarcomas form ∼3.6% of all the histological subtypes. They have an
atypical clinical presentation and, more commonly, mimic pulmonary thromboembolism,
thereby implicating the essential role of multiple noninvasive imaging modalities
in distinguishing them and aiding in their early diagnosis. The treatment consists
of surgical resection and chemotherapy. Here we report a rare case of multicentric
primary pulmonary artery angiosarcoma with substantial extension into lung.
Case Presentation
A 68-year-old male presented with 2 weeks history of breathlessness on exertion and
weight loss of approximately 10 kg over the last 2 years. There were no complaints
of chest pain, palpitation, or fever. He was a known diabetic and hypothyroid, and
was on regular medications. On examination, vitals were stable. Blood investigations
were normal except for an elevated C-reactive protein (75 mg/L).
The clinical diagnosis was of pulmonary thromboembolism (PTE). However, the chest
radiograph revealed a well-defined opacity in the left parahilar region ([Fig. 1]). Computed tomography (CT) pulmonary angiogram revealed a well-defined, 5.6 × 5.3 cm
sized rounded lesion in the superior segment of the left lower lobe, just extending
into the apicoposterior segment of the left upper lobe of lung causing complete obliteration
of the left pulmonary arterial tree from distal left pulmonary artery onward. There
was patchy, eccentric, minimal enhancement of this lesion (Hounsfield Unit [HU] of
21 on plain and 41 on contrast) ([Fig. 2]). Small ground glass nodules were seen in the inferior aspect of this lesion. A
focal filling defect sized 2.7 × 1.3 cm was seen at the root of the main pulmonary
artery, which also revealed enhancement (HU of 25 on plain and 61 on contrast) ([Fig. 2]). The main pulmonary artery was dilated, suggestive of pulmonary hypertension. There
was mild volume loss of the left lung with oligemia ([Fig. 2]). With these findings, the possibilities considered were primary pulmonary artery
sarcoma (PAS), primary lung malignancy, and thrombosed pulmonary artery aneurysm.
Fig. 1 Frontal chest radiograph shows a well-defined rounded opacity in the left parahilar
region (black arrow).
Fig. 2 (A, B) Axial computed tomography pulmonary angiogram (CTPA) images show patchy minimal
peripheral enhancement (white arrows) of the large mass lesion with Hounsfield Unit
(HU) of 28 and 41 in the early and delayed phases, respectively, occluding the distal
left pulmonary artery. (C) Axial CTPA image shows minimally enhancing filling defect in the root of the pulmonary
artery with HU of 61 (black arrow). (D) Coronal maximum intensity projection image showing normal right pulmonary arterial
tree (black arrow) and complete nonopacification distal left PA onward with corresponding
left lung oligemia (white arrows).
In view of the conflicting nature of the lesion, magnetic resonance imaging (MRI)
was done. The lesion was hypoisointense on T1-weighted images, heterogeneously hyperintense
on T2-weighted images (T2WI) with central hypointensity on gradient recalled echo
images and mild restricted diffusion ([Fig. 3]). There was enhancement in the central and medial part of the lesion on arterial
phase with progressive diffuse enhancement of the lesion on delayed phases. The lesion
at the root of the pulmonary artery, just distal to the pulmonary valve, appeared
mildly hyperintense on T2WI and showed subtle post-gadolinium enhancement ([Fig. 4]).
Fig. 3 Magnetic resonance imaging thorax. Arrows show the two lesions appearing isohypointense
on T1-weighted image (A), heterogeneously hyperintense on T2-weighted image (B), with central gradient recalled echo hypointensity (C) and hyperintense on PDFS images (D).
Fig. 4 Post-contrast magnetic resonance images: (A, B) Medial and central lesional enhancement (white arrows) in the arterial phase with
progressive diffuse enhancement on the delayed phases with occlusion of the left main
pulmonary artery distally. (C) Small enhancing lesion within the root of the main pulmonary artery (arrow). (D) Classical demonstration of left lung oligemia secondary to occlusion of the left
main pulmonary artery (arrow).
On further evaluation with fluorodeoxyglucose positron emission tomography-computed
tomography (FDG PET-CT), the lesion revealed heterogeneous intensely increased FDG
uptake with SUVmax of 10.7. Central necrotic areas with no FDG uptake were seen. Moderately increased
FDG uptake was seen in the filling defect at the root of the pulmonary artery with
SUVmax of 6.3 on the baseline images that increased to 9 on the delayed scan ([Fig. 5]). No other FDG avid area was seen. These findings were highly suggestive of neoplastic
etiology, most likely a multicentric angiosarcoma.
Fig. 5 Fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT):
(A) Initial and (B) delayed. Arrows show a large lesion with heterogeneous increased uptake and another
lesion at the root of the pulmonary artery, with increased uptake on delayed images.
Arrowhead marks central non-FDG avid area of necrosis within the lesion.
To confirm the same, a CT-guided transthoracic biopsy of the larger lesion was done
under local anesthesia by posterior approach and sent for histopathological analysis
([Fig. 6]). The microscopy of the biopsy cores revealed high-grade spindle cell sarcoma, showing
cytologic atypia, mitotic figures, and foci of necrosis. Immunohistochemistry showed
focal expression of epithelial membrane antigen, ETS-related gene, and CD31 and was
negative for cytokeratin (AE1/AE3), thyroid transcription factor-1, P 63, desmin,
smooth muscle antigen, h-caldesmon, S-100 protein, and CD34. These histopathological
features were suggestive of a high-grade spindle cell sarcoma, consistent with an
angiosarcoma.
Fig. 6 Computed tomography (CT)-guided biopsy of the mass lesion by posterior approach.
(A) Needle tract. (B) Post-biopsy plain axial CT with air foci within (arrows).
Thus, with two separate enhancing, FDG avid lesions and with histology as described
above, the diagnosis of multicentric primary pulmonary artery angiosarcoma was established.
Discussion
PAS are neoplasms with origin from the mesenchymal cells of the intimal layer of the
pulmonary artery. The occurrence of primary PAS is so rare, only ∼0.001 to 0.03%,[1] that though the first case was described in 1923, thereafter its description has
been limited to case reports and case series. A total of ∼391 cases have been described
thus far in literature.[2] Among the sarcomas of the great vessels, PAS are the most common, affecting the
trunk (80%), the right pulmonary artery (57%), and the left pulmonary artery (58%),
both the arteries in 37% and the pulmonary valve in 29%.[3] Angiosarcomas are estimated to have an incidence of ∼3.6% among the various types
of PAS.[4]
PAS can present with varied symptoms that may mimic PE. However, they can even be
completely asymptomatic initially and cause short duration of symptoms only at an
advanced stage, like in unilateral extension into the lung from peripheral involvement
of the pulmonary artery,[5] as observed in our case. Shortness of breath is the most common presenting symptom,
others being chest pain, cough, hemoptysis, weight loss, fatigue, dizziness, and fever.[2] Lack of predisposing factors for thromboembolism, persistent symptoms, recurrence
despite adequate anticoagulation, and unilateral massive perfusion defect should raise
the possibility of tumoral obstruction.[6] The differential diagnoses include pulmonary thromboembolism and lung neoplasm.
CT helps differentiate PAS from PE by indicating a low-attenuation filling defect
occupying the entire luminal diameter of the proximal or main pulmonary artery, expansion
of the involved arteries, or extraluminal tumor extension.[7] In our case, filling defect was seen in distal left pulmonary artery with extraluminal
tumor extension. PAS on CTPA has been demonstrated to show eclipsing of the pulmonary
artery wall before it infiltrates beyond the artery, absent in PE, termed as the wall
eclipsing sign and defined as almost full occupation of the lumen of the pulmonary
trunk, left pulmonary artery or right pulmonary artery by a low-density mass; protrusion
of the proximal end of this mass toward the right ventricular outflow tract; and eclipsing
of one or both walls of the artery by the lesion.[8] Though this could be a useful sign assisting in the diagnosis of PAS, it was not
visualized in our case, most likely due to substantial extension of the tumor into
the adjacent lung, beyond the left pulmonary artery.
Multiparametric MRI findings of PAS include hyperintense filling defect in the main
pulmonary artery on fat suppressed T2-weighted and diffusion-weighted imaging and
contrast enhancement.[9] These findings were also observed in our case.
Potential benefits of metabolic imaging using F-18 FDG PET-CT have been sporadically
described in the literature. Unequivocal positive findings with mean SUVmax of 13.1 have been described for PAS.[10] The mean SUVmax of 7.6 was significantly higher in PAS than PE.[11] Our case also revealed significantly higher FDG uptake in both the lesions that
favored the diagnosis of PAS. PET-CT being a whole-body examination helps to decide
on the possible malignant nature of a filling defect and also serves as a staging
modality.[10] Thus, FDG PET-CT should also be considered as part of the imaging workup in a case
of suspected PAS.
Conclusion
Thus, in a clinical setting of high index of suspicion, multimodal imaging approach
should be made use of, so that prompt diagnosis and timely institution of appropriate
treatment can be made, thereby improving the prognosis. The definitive diagnosis,
however, is achieved only by histopathology.
