Key Words
Aortic dissection - Vasa vasorum - Intramural hematoma
Introduction
The natural history of intramural hematoma (IMH) in the aorta remains difficult to
define. A number of investigators have reported on factors that predict whether IMH
will progress to formal aortic dissection (AD) or regress with complete resolution[1]. A consensus of opinion has developed that IMH in the ascending aorta and descending
aorta should be treated as for formal Type A and Type B dissection, respectively[2]. However, it is known that roughly a third to a half of IMHs will regress with medical
management[3]. The exact pathological evolution of this process has remained undefined. Intercostal
artery rupture has been identified as part of the process of an acute aortic syndrome
in an analysis of imaging follow-up data[4]. It is generally thought that rupture of vasa vasorum leads to the development of
IMH and that expansion of the tunica media causes longitudinal distraction of the
intercostal artery as it crosses the aortic mura, and this leads to rupture of the
intercostal artery. Coalescence of blood from this rupture may lead to formal dissection.
In this report we present the case of a patient who demonstrated clear images of intercostal
artery rupture during the process of expansion of IMH in a Type B acute aortic syndrome.
Of unique interest is the demonstration of complete resolution of this pathology with
medical management.
Case Presentation
A 63-year-old female presented to the Accident and Emergency Department of a District
General Hospital with unremitting chest pain radiating to the intrascapular region.
She had a documented history of hypertension. She had no cardiac family history and
no other comorbidities. On examination, her blood pressure was 210/115 mm Hg in both
arms with a regular pulse of 92 bpm. There was no pulse deficit or cardiac murmur,
and no neurological deficit. Laboratory workup was normal. A 12-lead ECG showed normal
sinus rhythm with no ischemic changes. She underwent a contrast-enhanced CT scan of
the chest and abdomen ([Fig. 1]).
Figure 1. Contrast-enhanced CT scan of the thoracic aorta demonstrating several small collections
of contrast in the intramural hematoma representing inflow from the intercostal arteries.
There is good perfusion to the celiac axis superior mesenteric artery and renal arteries.
The CT scan demonstrated a normal caliber aortic root and ascending aorta. There was
a common origin of the left common carotid and innominate artery. The left subclavian
artery was normal in appearance, and an aberrant right subclavian artery with a thickened
wall was present. There was an intramural hematoma extending from the proximal descending
thoracic aorta, immediately distal to the left subclavian artery, which extended through
to the midabdominal aorta, terminating just superior to the inferior mesenteric artery.
Several small collections of contrast were seen within the thickened wall, which is
most likely caused by inflow from ruptured intercostal arteries ([Figs. 1] and [2]). The maximal diameter of the descending aorta was 4.7 cm. A large left pleural
effusion was noted on the scan with normal lung parenchyma and no hilar or mediastinal
lymphadenopathy. The celiac axis, the superior mesenteric artery, and the renal arteries
were adequately perfused. Otherwise, there were no other abnormalities noted.
Figure 2. Close up of contrast-enhanced CT scan of the thoracic aorta demonstrating a small
collection of contrast in the intramural hematoma representing inflow from the intercostal
arteries.
The patient was immediately transferred to our center for further stabilization. She
was admitted to the intensive care unit and started on intravenous infusion of labetalol
to control her blood pressure. Over a period of 1 week, she was weaned from intravenous
β-blockers to oral hypertensive medications. She was discharged home and regular follow-up
was organized. Her current status, a further 2 years later, is stable. CT scans reveal
no change in the size of her aorta and a regression of the IMH and pleural effusion
([Fig. 3]). She continues with medical management and yearly surveillance.
Figure 3. Follow up contrast-enhanced CT scan demonstrating a regression of the collections
and IMH.
Discussion
Intramural hematoma is part of a spectrum of disease known as acute aortic syndrome
and includes other pathologies such as intimal tear, penetrating atherosclerotic ulcers,
and formal dissection. Hirst et al.[5] demonstrated that IMH was secondary to the rupture of vasa vasorum within the media
and subadventitia. A functional definition of IMH, from the perspective of flow, is
that it is a blood collection within the aortic wall, not freely communicating with
the lumen, with restricted flow[6]. IMH comprises 10-30% of acute aortic syndrome[7]. The interesting behavior of IMH is that it may progress to formal dissection or
regress to complete resolution[4]
[5]
[6]
[7]. Predicting its behavior has significant clinical consequence as surgery may be
avoided if there is confidence that with appropriate medical management the pathology
may resolve.
Whether the right aberrant subclavian artery encountered in this case report may have
contributed to the IMH remains a possibility, but a challenge to prove. Penetrating
atherosclerotic ulcer, classic aortic dissection, and aortic rupture may have similar
clinical manifestations; however, they are radiologically distinguishable. The CT
features of penetrating ulcers include focal involvement with adjacent subintimal
hematoma located beneath the frequently calcified and inwardly displaced intima in
the middle or distal third of the thoracic aorta. The ulcer is often associated with
thickening or enhancement of the aortic wall[8].
Moreover, an interesting observation made previously is that expansion of IMH may
cause rupture of intercostal arteries in their transmural portion leading to coalescence
of pools of free blood within the wall of the aorta, so-called “aortic branch artery
pseudoaneurysms”[7]. It is conceivable that such pseudoaneurysms and pooling of blood within the media
is one possible intermediary step in the evolution to formal dissection. What has
not been demonstrated so clearly before is that this phenomenon is clearly not an
irreversible step. The patient presented here shows clearly the presence of aortic
branch pseudoaneurysms and that with medical management there is complete resolution
to normal size and morphology of the aorta.
Conclusion
Expanding intramural hematoma may cause rupture of intercostal and bronchial arteries
in the transmural portion as they cross the tunica media of the aorta. This leads
to pseudoaneurysms, which may be an intermediary step in the evolution of aortic dissection.
Intercostal rupture is not an irreversible step, and our case presentation demonstrates
reversibility of the process with good medical management.
