Ductus Arteriosus and its Remnants in Adults

The ductus arteriosus involutes during infancy, sometimes leaving a small remnant called the ductus bump or diverticulum. It can also remain patent into adulthood or form into an aneurysm.

A ductus bump or diverticulum is a focal outpouching of the proximal descending aorta and is a normal variant, not to be confused with either a patent ductus arteriosus, aneurysm, or pseudoaneurysm.

Aneurysm of the ductus diverticulum is rarely seen in adults . Patients may present with hoarseness, dyspnea, hemoptysis, and/or cough. The aneurysm can erode into a bronchus, the esophagus, pericardium, or pleural cavity, with disastrous consequences. Risk of rupture increases when the aneurysm is larger than 3 cm. The main differential consideration for a ductus aneurysm is just a regular aortic arch aneurysm. Three dimensional reconstructions help by showing ductus aneurysms pointing toward the left pulmonary artery.

A traumatic pseudoaneurysm is also a consideration. They tend to occur in the region of the isthmus and usually form an acute angle with the aorta, unlike the more gentle obtuse angle of the ductus bump.

On the axial images, we see a rounded structure (pink arrow) arising from the aortic arch (blue arrow) and heading toward the left pulmonary artery. At this point, we could be dealing with a patent ductus arteriosus or a diverticulum. The fact that the study was done without intravenous contrast limits our evaluation of this incidental finding in a 70-year-old woman, but coronal and sagittal oblique maximum intensity projections help a bit. In the case of a diverticulum, we'd expect to see a plane between the structure and the left pulmonary artery, but we don't see one here.

References

• Goitein O, Fuhrman CR, Lacomis JM. Incidental finding on MDCT of patent ductus arteriosus: use of CT and MRI to assess clinical importance. AJR Am J Roentgenol. 2005 Jun;184(6):1924-31.
• Lee EY, Boiselle PM, Cleveland RH. Multidetector CT evaluation of congenital lung anomalies. Radiology. 2008 Jun;247(3):632-48
• Sugimoto T, Takahashi T, Inui K, Minowa T, Watanabe T, Shimazaki Y. Aneurysm of the ductus diverticulum in adults: the diagnostic value of three-dimensional computed tomographic scanning. Jpn J Thorac Cardiovasc Surg. 2003 Oct;51(10):524-7.

Left Aortic Arch with an Aberrant Right Subclavian Artery

Left aortic arch and aberrant right subclavian artery (ARSCA) is commonly referred to as the most common congenital arch anomaly, affecting 1% of the population. Sometimes the statement is qualified by noting that the so-called bovine arch, which occurs in ~15% of the population, is actually more common.

An aberrant right subclavian artery refers is a right subclavian artery that arises from the aortic arch distal to the left subclavian artery origin. The ARSCA then may travel posterior to esophagus (most common course), between the trachea and esopahgus (~20% of cases), or anterior to the traches (~5% of cases).

While dysphagis lusoria, described in 1794 by David Bayford as a lusus naturae (freak or jest of nature), was in reference to dysphagia due to an aberrant right subclavian artery, most people with left aortic arch and ARSCA are asymptomatic. About a third do experience symptoms, with dysphagia being the complaint in about 90% of cases. Airway symptoms may also occur, but are much less common.

The diagnosis is easy on cross sectional imaging. Chest radiographs do not demonstrate the anomaly directly, but in the rare case of coarctation of the aorta proximal to an ARSCA, unilateral left rib notching may be seen.

An aberrant right subclavian artery is more than just an incidental finding or a trivia question about unilateral left rib notching. It's important to make note of it for many reasons:

• Head and neck surgeons will want to know about this because of the association of ARSCA with a nonrecurrent laryngeal nerve (NRLN). A NRLN is a laryngeal nerve that leaves the vagus nerve in the neck to directly innervate the larynx, instead of swinging down below the arch. The nerve can be inadvertently injured in carotid artery or thyroid procedures if this anomalous course is not suspected.
• Thoracic surgeons will want to know about this because of the association with an aberrant course of the thoracic duct. In addition, clamping the aorta proximal to the left subclavian artery during surgery will occlude both vertebral arteries, which will lead to brainstem infarction.
• Pediatric cardiologists will want to know about an ARSCA, because it is found in 35% of children with Down syndrome who have other cardiac anomalies. An ARSCA in a child with Down syndrome should prompt further investigation.
• Trauma surgeons will care because an aortic dissection may extend into the ARSCA, which may perforate into the esophagus and lead to exsanguination.

Here we see an aberrant right subclavian artery (pink arrow) arising from a diverticulum of Kommerell (blue arrow) and traveling posterior to the esophagus.

References

• Donnelly LF, Fleck RJ, Pacharn P, Ziegler MA, Fricke BL, Cotton RT. Aberrant subclavian arteries: cross-sectional imaging findings in infants and children referred for evaluation of extrinsic airway compression. AJR Am J Roentgenol. 2002 May;178(5):1269-74.
• Proto AV, Cuthbert NW, Raider L. Aberrant right subclavian artery: further observations. AJR Am J Roentgenol. 1987 Feb;148(2):253-7.

Intrapulmonary Lymph Nodes

One of the main reasons people go into radiology is the promise that one day, if they play their cards right, they can spend half their day doing nothing but hunting nodules on chest CTs ordered for "cough." Not uncommonly, we come across peripheral nodules that may or may not be intrapulmonary lymph nodes.

At least two papers (one from our institution back in 1996, and a recent one from NYC) have described the CT appearance of these intrapulmonary lymph nodes. They tend to be predominantly in the lower lobes and in the right middle lobe, all below the carina.

They can range in size from a few mm to 9 mm and are located within 20 mm of the chest wall, with the ones farthest away from the chest wall abutting fissures. The nodules are sharply defined and uncalcified. They may have a discrete thin tag or thickened interlobular septum extending to the pleural surface.

References

• Bankoff MS, McEniff NJ, Bhadelia RA, Garcia-Moliner M, Daly BD. Prevalence of pathologically proven intrapulmonary lymph nodes and their appearance on CT. AJR Am J Roentgenol. 1996 Sep;167(3):629-30.
• Shaham D, Vazquez M, Bogot NR, Henschke CI, Yankelevitz DF. CT features of intrapulmonary lymph nodes confirmed by cytology. Clin Imaging. 2010 May-Jun;34(3):185-90.

Radiographic Findings in Aortic Trauma

The most reliable signs of mediastinal hemorrhage on supine radiographs are an abnormality of the aortic contour or the presence of one or more of the following:

• Transverse mediastinal width > 8 cm just above the aortic knob
• Apical cap sign
• Widening (> 5 mm) of the right paratracheal stripe
• Deviation of the nasogastnic tube to the right of the T4 spinous process

We can achieve a sensitivity of 93% and specificity of 60% for ruptured aorta in a trauma patient with evidence of mediastinal hemorrhage if at least one of these two signs is present:

• Deviation of the nasogastnic tube to the right of the T4 spinous process
• Widening (> 5 mm) of the right paratracheal stripe

When both the nasogastric tube and trachea are deviated to the right, we have a 96% chance of having an aortic rupture, and some feel that this is a very specific sign for aortic rupture.

Displacement of the left mainstem bronchus inferiorly and to the right can be seen with mediastinal hemorrhage and has been advocated as a specific sign of aortic isthmus rupture

Signs such as an increased (> 0.25) mediastinal width to chest width ratio, tracheal deviation to the right of midline, left hemothorax without associated rib fracture, widening of the paraspinal lines, and aortopulmonary window opacification do not reliably separate patients with mediastinal hemorrhage from normal.

References

Woodring JH, Loh FK, Kryscio RJ. Mediastinal hemorrhage: an evaluation of radiographic manifestations. Radiology. 1984 Apr;151(1):15-21.

Reversed Halo Sign

The reversed halo sign, also known as the atoll sign, refers to a round area of ground-glass attenuation surrounded by a crescent (> 3/4 of a circle) or ring of airspace consolidation that is greater than 2 mm in thickness.

The reversed halo sign has been classically described in cryptogenic organizing pneumonia, but can be seen in a number of conditions. Recently it has been suggested that nodularity of the ring can be used to differentiate granulomatous infections and active sarcoidosis from cryptogenic organizing pneumonia, which has a smoother ring.

Differential considerations include:

• Cryptogenic organizing pneumonia (COP): Classical description of the reversed halo sign. Seen in up to 20% of patients with COP and thought to be fairly specific, although it can be seen in other conditions.
• Infections: Cryptococcosis, South American blastomycosis (paracoccidioidomycosis), schistosomiasis, pneumonococcal pneumonia, tuberculosis.
• Vasculitides: Wegener granulomatosis, dermatomyositis.
• Sarcoidosis:
• Lymphomatoid granulomatosis: Rare Epstein-Barr virus–associated lymphoproliferative disease, characterized by vascular destruction, classically in the lungs.

References

• Agarwal R, Aggarwal AN, Gupta D. Another cause of reverse halo sign: Wegener's granulomatosis. Br J Radiol. 2007 Oct;80(958):849-50.
• Algin O, Gokalp G, Topal U. Signs in chest imaging. Diagn Interv Radiol. 2010 Jul 28.
• Benamore RE, Weisbrod GL, Hwang DM, Bailey DJ, Pierre AF, Lazar NM, Maimon N. Reversed halo sign in lymphomatoid granulomatosis. Br J Radiol. 2007 Aug;80(956):e162-6.
• Gasparetto EL, Escuissato DL, Davaus T, de Cerqueira EM, Souza AS Jr, Marchiori E, Müller NL. Reversed halo sign in pulmonary paracoccidioidomycosis. AJR Am J Roentgenol. 2005 Jun;184(6):1932-4.
• Kim SJ, Lee KS, Ryu YH, Yoon YC, Choe KO, Kim TS, Sung KJ. Reversed halo sign on high-resolution CT of cryptogenic organizing pneumonia: diagnostic implications. AJR Am J Roentgenol. 2003 May;180(5):1251-4.
• Kumazoe H, Matsunaga K, Nagata N, Komori M, Wakamatsu K, Kajiki A, Nakazono T, Kudo S. "Reversed halo sign" of high-resolution computed tomography in pulmonary sarcoidosis. J Thorac Imaging. 2009 Feb;24(1):66-8.
• Marchiori E, Grando RD, Simões Dos Santos CE, Maffazzioli Santos Balzan L, Zanetti G, Mano CM, Gutierrez RS. Pulmonary tuberculosis associated with the reversed halo sign on high-resolution CT. Br J Radiol. 2010 Mar;83(987):e58-60.
• Marchiori E, Zanetti G, Hochhegger B, Irion KL. Re: Reversed halo sign: nodular wall as criterion for differentiation between cryptogenic organizing pneumonia and active granulomatous diseases. Clin Radiol. 2010 Sep;65(9):770-1.
• Tokuyasu H, Isowa N, Shimizu E, Yamadori I. Reversed halo sign associated with dermatomyositis. Intern Med. 2010;49(15):1677-8.
• Tzilas V, Bastas A, Provata A, Koti A, Tzouda V, Tsoukalas G. The "reversed halo" sign in pneumonococcal pneumonia: a review with a case report. Eur Rev Med Pharmacol Sci. 2010 May;14(5):481-6.
• Voloudaki AE, Bouros DE, Froudarakis ME, Datseris GE, Apostolaki EG, Gourtsoyiannis NC. Crescentic and ring-shaped opacities. CT features in two cases of bronchiolitis obliterans organizing pneumonia (BOOP). Acta Radiol. 1996 Nov;37(6):889-92.

Nuclear Medicine and Liver Lesions

Remembering which lesions do what with which radiotracers can be more difficult than understanding this sentence. Some (perhaps over-simplified) points:

• Tc-99m sulfur colloid: Shows Kupffer cell activity.
• Tc-99m HIDA: Shows hepatocyte function.
• Tc-99m red blood cell: Shows tumor vascularity.

Focal nodular hyperplasia (FNH) has hepatocytes but disorganized biliary canaliculi. As a result, it will take up HIDA rapidly, but because of the disorganized biliary canaliculi, will keep the tracer around longer than the rest of the liver. FNH also has Kupffer cells of varying function; therefore, most are indistinguishable from the rest of the liver on sulfur colloid, but they may infrequently be cold or hot. FNH is a vascular tumor, so tagged red blood cell scans will show early uptake with or without persistent uptake on delayed images.

Adenomas are derived from hepatocytes, but and may show uptake on HIDA. They don't have that many Kuppfer cells, however, so the majority will be cold on sulfur colloid, but about 20% will be warm. Adenomas are vascular tumors, so tagged red blood cell scans will show early uptake with or without persistent uptake on delayed images.

Hepatocellular carcinoma (HCC) is also derived from hepatocytes, but these mutated hepatocytes may or may not function that well, so about 50% of HCCs will show uptake on HIDA and may be associated with a better prognosis. Whatever Kuppfer cells there may have been in the beginning are overrun by the cancer, so HCC is usually cold on sulfur colloid imaging in cirrhotic livers. HCC is a vascular tumor, so tagged red blood cell scans will show early uptake with or without persistent uptake on delayed images.

Hemangiomas are a tangle of vessels that takes up space amidst normal hepatocytes and Kuppfer cells, so they will be cold on sulfur colloid and HIDA scans. Tagged red blood cell scans will show a focal cold spot on early images and persistent filling on delayed images. This is the same as its behavior on dynamic CT, since we're basically following blood in both modalities.

Finally, liver metastases are alien to the liver, so they will not pick up hepatocyte or Kuppfer cell agents, appearing cold on sulfur colloid and HIDA scans.

References

• Mettler FA and Guiberteau MJ. Chapter 8. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 203-242.
• Schulze PJ, Stritzke P, Stolzenbach G. Liver imaging and detection of liver metastases with 99mTc-HIDA. Nuklearmedizin. 1981 Oct;20(5):214-9.

Duplex Evaluation of the Carotid Arteries

Degree of stenosis	ICA PSV (cm/s)	Plaque	ICA/CCA PSV ratio	ICA EDV (cm/s)
Normal	<125	None	< 2.0	<40
< 50%	<125	<50%	< 2.0	<40
50%-69%	125-230	≥50%	2.0-4.0	40-100
≥70<near occlusion	>230	≥50%	> 4.0	> 100
Near-occlusion	Anything goes	Visible	Anything goes	Anything goes
Total occlusion	Undetectable	No detectable lumen	NA	NA

A tight stenosis in an internal carotid artery (ICA) can cause falsely elevated peak systolic and end diastolic velocities in the contralateral ICA evaluated by duplex ultrasound. This artifactually increased velocity can lead to a false positive diagnosis of a stenosis. One explanation put forward is that the increased flow is caused by cross filling via the circle of Willis to the cerebral hemisphere on the same side as the tight stenosis. Unfortunately, this has not been confirmed by angiography. In any case, if you see a velocity increase out of proportion to real-time vessel characteristics (i.e., large plaque), you should do a careful evaluation for high-grade stenosis of the contralateral ICA.

Aortic regurgitation can present with different findings on carotid duplex. Aortic regurgitation results in reflux of blood from the aorta back into the left ventricle, and causes a widened pulse pressure and increased stroke volume. Ejection fraction may be normal or high early on, but as left ventricular decompensation occurs with longstanding aortic regurgitation, the ejection fraction normalizes and then drops.

A bisferious pulse, also known as pulsus bisferiens, is the presence of two systolic peaks that can be seen in pressure tracings of the the ascending aorta, the aortic arch, and the carotid artery in patients with aortic regurgitation with or without concurrent aortic stenosis. It can also be seen in patients with severe obstructive hypertrophic cardiomyopathy.

Reversal of diastolic flow direction can also be seen in the carotid arteries of patients with aortic regurgitation

Aortic stenosis can cause a characteristic tardus-parvus waveform: prolonged systolic acceleration time (tardus) with low peak systolic velocity (parvus). Bilateral tardus-parvus waveforms in the carotids can be seen with aortic stenosis. In general a tardus-parvus waveform is indicative of a severe stenosis proximal to the point of measurement. For example when sampling distal renal artery branches in a patient with renal artery stenosis.

Right subclavian steal can be reflected in the carotids as a tardus-parvus waveform of the right common and internal carotid arteries.

Cardiac dynamic factors can also affect the carotid waveform. Hypertension can result in high flow (> 135 cm/s) in both common carotid arteries, whereas poor cardiac output can lead to low flow (< 45 cm/s) in both common carotid arteries.

Bradycardia, by allowing longer diastolic filling of the left ventricle, produces increased stroke volume and increased systolic velocities in the carotids. The prolonged diastolic time also leads to a longer diastolic runoff and spuriously decreased end diastolic values.

References

• Beckett WW Jr, Davis PC, Hoffman JC Jr. Duplex Doppler sonography of the carotid artery: false-positive results in an artery contralateral to an artery with marked stenosis. AJR Am J Roentgenol. 1990 Nov;155(5):1091-5.
• Kallman CE, Gosink BB, Gardner DJ. Carotid duplex sonography: bisferious pulse contour in patients with aortic valvular disease. AJR Am J Roentgenol. 1991 Aug;157(2):403-7.
• Tahmasebpour HR, Buckley AR, Cooperberg PL, Fix CH. Sonographic examination of the carotid arteries. Radiographics. 2005 Nov-Dec;25(6):1561-75.