|ECR 2019 / C-2382|
|Diverticular lesions of the thorax: a comprehensive review.|
Findings and procedure details
We classify diverticula by their localization inside the thorax:
Airway (tracheal and bronchial diverticulum).
Esophagus (Zenker and Killian diverticulum, traction and epiphrenic diverticulum).
Cardiac (ventricular diverticula, myocardial clefts and atrial diverticula).
Pericardium (pericardial diverticulum and pericardial cyst).
Vascular (Kommerell and ductus diverticulum).
Neural (radicular cyst and meningocele).
We review imaging findings and discuss potential pitfalls and differential diagnosis.
Tracheal diverticula (TD) represent outpouchings that can be filled with air or mucus.
Congenital diverticula are composed of muscle and cartilage and represent remnants of an aborted division of the primary lung bud.
Acquire diverticula are simple little evaginations of the mucosa through a weak point. They can be cause by prolonged increased of intraluminal pressure (e.g. due to a chronic cough or COPD), or external traction (e.g. adenopathy or pulmonary fibrosis).
Both are typically located in posterolateral position on the right side. Less frequently acquired ones can be located at other levels, be larger and have septa inside (atypical presentation) (Fig. 2).
Paratracheobronchial structures containing air (Zenker’s diverticulum, apical lung hernia or bulla and tracheal bronchi) should be included in the differential diagnosis.
BRONCHIAL DIVERTICULA (BD)
Less frequent than tracheal diverticula.
They can occur on both sides of the bronchial tree (Fig. 3).
Generally, 1- to 3-mm outpouchings, may be single or multiple, as frequently seen in association with chronic obstructive pulmonary disease (COPD) (Fig. 4), or even as a diverticulosis in Mounier-Kuhn disease.
May be secondary to traction phenomena, usually in relation with adenopathy (Fig. 20 : D, E and F) or pulmonary fibrosis.
The presence of cartilage may suggest a congenital origin. Nevertheless, it remains difficult to demonstrate these features with CT.
Both TD and BD are generally asymptomatic and can coexist; they can present clinical symptoms related to infection. The knowledge of their presence is important to avoid complications as iatrogenic perforation.
Tracheobronchomegaly or Mounier-Kuhn syndrome associates TD and BD (Fig. 5). It is caused by the absence or marked atrophy of the elastic fibers and smooth muscle within the wall of the trachea and main bronchi.
Diagnosis is based on imaging criteria:
Tracheal diameter > 3 cm, generally associated with tracheal and bronchial diverticula and bronchiectasis (Fig. 6).
AIRWAY DIVERTICULA: PITFALLS
Tracheal bronchus (TB) originates directly from the trachea or main bronchi (usually within 2 cm and up to 6 cm of the carina (Fig. 7 : A and B) (Fig. 8), generally ventilating part of the superior right upper lobe.
An incomplete or atretic TB may present as a diverticulum at CT and bronchoscopy (Fig. 7 : C). Differential diagnosis is generally based on its location.
ACCESSORY CARDIAC BRONCHUS
The accessory cardiac bronchus (ACB) generally originates in the medial wall of the intermediate bronchus.
Typical ACB appears as a saccular diverticular image with smooth margins without connection with adjacent pulmonary parenchyma (Fig. 9).
Infrequently direct connection between ACB and distal bronchi and parenchyma can be appreciated (Fig. 10).
ACB and TB can also be associated (Fig. 11).
The esophageal bronchus is a rare condition where a diverticular image, representing an accessory bronchus arises directly from the esophagus (Fig. 12) (Fig. 13). It is more commonly describe in females and can be associated with esophageal atresia and tracheoesophageal fistula.
A rare, but serious complication of endotracheal intubation, especially when tracheal diverticula coexist.
It is generally located in the posterior membranous wall of the trachea. The presence of pneumomediastinum is key in the differential diagnosis (Fig. 14).
The presence of endobronchial material, as mucous plug or blood clot, can generate diverticular like images. MPR reconstructions are helpful for a correct diagnosis (Fig. 15).
Esophageal diverticula are sac or pouch projections arising from the esophagus, due to an increased pressure or traction.
They can be classified according to different aspects:
True : include all esophageal layers
False: contains only mucosa and submucosa herniating through the muscular layer.
Mechanism of formation:
Traction : secondary to pulling forces on the outer aspect of the esophagus.
Pulsion : secondary to increased intraluminal pressure.
Upper esophageal : Zenker diverticulum and Killian-Jamieson diverticulum
Middle esophageal : traction, pulsion and aortopulmonary window diverticula
Lower esophageal : epiphrenic diverticula.
ZENKER DIVERTICULUM (ZD)
ZD is a false, pulsion and upper esophageal (hypopharyngeal) diverticulum. Protrudes through a triangular weak site (cricopharyngeus dysfunction), between horizontal and oblique components of cricopharyngeus muscle, in the posterior wall (Killian's dehiscence). More than 50% of the affected patients present in 60-80 years.
At neck or chest radiographs appears as a mass, typically located at the C5-6 level, frequently with air-fluid level.
The esophagram shows a collection with midline posterior origin just above cricopharyngeus muscle protruding lateral, usually to left, and caudal with enlargement (Fig. 16).
CT demonstrates a generally large diverticulum with air-fluid level, depending from the superior portion of the esophagus, with a posterior neck at the level of the cricoid cartilage (Fig. 17). CT allows a correct differential diagnosis from TD, generally without air-fluid level and narrow neck.
KILLIAN-JAMIESON DIVERTICULUM (KJD)
KJD is a false, pulsion and upper esophageal (hypopharyngeal) diverticulum. Protrudes through a lateral anatomic weak site of the cervical esophagus below the cricopharyngeus muscle (Killian-Jamieson area). CT allows demonstrate a left sided location (Fig. 18) or less commonly bilateral outpouching. They are smaller than Zenker diverticulum (usually <1.5 cm), and also rarely symptomatic.
AORTOPULMONARY WINDOW DIVERTICULUM (APD)
In APD, the normal esophagus transiently protrudes into the aortopulmonary window. Fixed protrusion is an inconsequential diverticulum (Fig. 19).
Secondary to fibrous changes on the adjacent structures of the esophagus (lung parenchyma, lymph nodes), generally affecting the middle esophagus. CT can demonstrate the direct causes of these diverticula (Fig. 20 : A, B and C).
EPIPHRENIC DIVERTICULUM (ED)
ED is a false, pulsion and lower esophageal type diverticulum.
Frequently located on the right posterolateral wall.
ED symptoms are dysphagia, regurgitation, compression or aspiration.
They are associated with: neuromuscular dysfunction, hiatus hernia, esophageal stricture, esophageal web.
On chest X-ray, they may appear as a retrocardiac soft tissue mass with or without an air-fluid level, mimicking a hiatus hernia. Fluoroscopy is the best imaging method. CT demonstrates diverticular morphology, eventual complications, as aspiration, or concomitant pathology as pulmonary fibrosis(Fig. 21).
VENTRICULAR DIVERTICULA (VD) AND VENTRICULAR CLEFTS (VC):
VD and VC are rare congenital outpouchings of the ventricular cavity.
Saccular outpouching structure that extends beyond the confines of the myocardium most frequently located in the left apex. Right VD are rare with only eighteen cases reported in literature (Fig. 22).
Contain all three myocardial layers
Display normal contraction (Fig. 23).
VD can be:
Congenital (no history of damage cause) (Fig. 24).
Acquired (utero viral infection, muscle and connective-tissue defects or excessive primordial-cell stimulation)
Association to midline thoracoabdominal defects (as Cantrell syndrome) and other congenital cardiac malformations is described.
Generally, asymptomatic but potentially responsible of complications (thrombosis, embolism, heart rupture, congestive heart failure, ventricular arrhythmias and valvular abnormalities).
Treatment is not established, generally individualized according to clinical characteristics of each patient, associated abnormalities and potential complications.
Narrow fissure-like outpouchings (also reported in literature as myocardial diverticula), most frequently located in the left ventricular side of the septum or inferior wall(Fig. 25).
Can affect also the right ventricle(Fig. 26).
More common than VD (approximately 2–3% of patients undergoing cardiac CT).
Do not extend beyond the margins of the myocardium
Obliterate during systolic contraction.
Associated with hypertrophic cardiomyopathy (increased prevalence among genotype-positive and phenotype-negative patients) (Fig. 27).
No adverse prognostic significance.
No treatment required.
VD and VC are important to distinguish from acquired ventricular aneurysms, particularly false aneurysms which carry a risk of rupture and require prompt attention.
Key imaging findings are:
Contraction on cine MR images or retrospectively gated CT, with myocardial thickening in VD and collapse of ventricular cavity in VC.
Lack of late gadolinium enhancement (LGE) at MR in VD and VC, indicative of absence of fibrosis inside the diverticular cavity.
Both MR and CT allow to define eventual presence of hypertrophic cardiomyopathy in VC patients (Fig. 27).
Complications as thrombi inside the cavity are infrequent in VD and are practically absent in VC.
Right VD must be distinguished from ventricular aneurysm, more frequent and generally associated with arrhythmogenic cardiomyopathy.
Ventricular aneurysm (VA)
VA is another lesion that can present a diverticular morphology.
Key imaging findings are:
Paradoxical motion (akinesis or dyskinesis) (Fig. 28).
LGE at MR (figure) indicative of myocardial fibrosis inside the aneurysm cavity.
Complications as thrombi inside the cavity are frequent and well depicted by MR or CT (Fig. 29).
Ventricular pseudoaneurysm (VP).
VP is a rupture of the LV free wall contained by the adjacent pericardium which prevents from extravasation and tamponade.
Causes are: MI, cardiac surgery, infectious endocarditis, and chest trauma.
Typically we can observe thin LGE (Fig. 33) representing the pericardium that constitute the fibrous wall of the pseudoanuerysm. As in VA thrombi can be detected and most severe complication is rupture.(Fig. 33)
LEFT ATRIAL DIVERTICULUM (LAD) AND LEFT ACCESSORY APPENDAGE (LAA):
- Pouch-like structure located in the atrial wall.
- Sac-like shape with a broad-based ostium and a smooth contour (Fig. 34).
- Frequent incidental finding (20% of patient undergoing cardiac CT).
- Typically located in the superior anterior atrial wall but can also be in other positions (Fig. 35).
- Less frequent than LAD (9% of patients undergoing cardiac CT).
- Small neck and an irregular contour, suggestive of presence of pectinate muscles (Fig. 36).
- Generally, affects the inferior lateral atrial wall (Fig. 37).
Both of these structures (Fig. 38):
- Are not associated with other cardiac congenital abnormalities in the majority of cases.
- May be associated with supraventricular arrhythmia.
- May be a possible cause of systemic embolic events during AF ablation.
Rare entities compared to LAD and LAA.
Congenital malformation with possible genetic origin.
Generally characterized by a saccular structure with small neck.
Associated with atrial tachyarrhythmias and Wolff-Parkinson-White syndrome.
Complications are compressive symptoms, progressive dilatation of the AD, formation of thrombi, rupture and sudden death. Hence, there is a recommendation for surgical resection for large diverticula.
CT and MRI (Fig. 39) are useful to differentiate them from pericardial cysts and mediastinal tumors.
Atrial septal aneurysm (ASA) is a diverticular saccular bulge of the interatrial septum, generally located at fossa ovalis level that protrudes to right, left or both atria(Fig. 40). ASA is a condition associated to cerebrovascular accident (sometimes linked to an interatrial shunt, usually a patent foramen ovale).
Diagnostic is commonly incidental through echocardiography, CT or MRI. In case of ASA, CT and MRI show:
• A focal outpouching of the interatrial septum of at least 10 mm
• A bulge with at least 15mm long at its basis
Due to its location or coexistent interatrial communication, CT and MR allows to differentiate it from an atrial diverticulum.
PERICARDIAL DIVERTICULAR IMAGES
PERICARDIAL DIVERTICULUM AND CYST
Incidental, rare, benign congenital malformations arising from the pericardium.
Diverticula can be radiologically identical to cysts, but they retain direct communication with the pericardial cavity and modify their size with changes in body position or breathing (Fig. 41). Cyst are generally located in the right cardiophrenic angle, have a constant size but may alter in shape (Fig. 42).
VASCULAR DIVERTICULAR IMAGES
KOMMERELL (Fig. 43)
Diverticular aortic image at the origin of an aberrant subclavian artery, potentially responsible of dysphagia.
Most frequently present in cases of right aortic arch with an aberrant left subclavian artery.
Possible complications is early calcified ateromatosis.
Kommerell-like diverticulum can be found in association with aberrant vertebral artery (Fig. 44).
DUCTUS DIVERTICULUM (Fig. 45)
The ductus diverticulum is and outpouching of the thoracic aorta in the correspondence of the aortic insertion of the ligamentum arteriosum.
NEURAL DIVERTICULAR IMAGES
Protrusion of meningothelial elements through a bone defect in the vertebral column. Generally located in the posterior area of the column. At CT or MR, they can appear as diverticular outpouchings in communication with the spinal canal(Fig. 48).
PERINEURAL CYST (TARLOV CYST)
Extradural meningeal cyst containing neural tissue, see as dilatation of the neural root sheath filled with cerebrospinal fluid (Fig. 49). They can cause remodeling or bone erosion.