Mediastinal Tumors Flashcards
Discuss mediastinal masses.
A variety of mediastinal masses may present in children.
In the anterior mediastinum, germ cell tumors and thymomas are the main diagnoses.
The need for thymectomy in a context of myasthenia will be discussed.
In the middle mediastinum, hematologic diseases (lymphomas) are the most common. An appropriate imaging is necessary.
Biopsies under general anesthesia need special precautions as the upper airways can collapse.
Finally, in the posterior mediastinum three types of foregut duplication cysts may be diagnosed: bronchogenic cysts, esophageal duplication cysts, and neuroenteric cysts.
Also, neurogenic tumors frequently occur in this anatomic compartment.
Foregut duplication cysts are generally not a surgical problem.
Thoracoscopy, whenever possible, should be used and favored over open surgery.
Which anatomic structures are located in the mediastinum and how is it divided?
The mediastinum is located in the chest and delimited laterally by the pleura of the right and the left lung.
It is bordered superiorly by the thoracic inlet, inferiorly by the diaphragm, anteriorly by the sternum and posteriorly by the vertebra.
Division of the mediastinum into specific anatomic compartments is mandatory to develop a differential diagnosis for a mediastinal mass identified on imaging.
In the anterior mediastinum the thymus and heart are located.
The trachea, carina, vena cava and aorta are part of the middle mediastinum.
In the posterior mediastinum esophagus, sympathetic ganglia chain, thoracic duct, vagus nerve and descending aorta are the main structures.
What is the most frequent localization of a pediatric mediastinal mass?
Posterior mediastinal masses are most frequent.
In a series of 120 cases, 44% tumors were located in the posterior mediastinum, 31% in the anterior and 25% in the middle mediastinum [2].
How many % of mediastinal masses are malignant in children?
50%. If a malignancy is suspected a collaboration with an oncologist is mandatory.
What masses are typical for each part of the mediastinum? [3, 4]
In the anterior mediastinum, the most common tumors include thymomas and ter- atomas followed by thymic cysts.
In the middle mediastinum, malignant hemo- pathies such as lymphoblastic tumors, Hodgkin disease, or mediastinal large cell non-Hodgkin’s lymphomas can develop.
Because of the surrounding structures, respiratory symptoms can occur related to the compression of the carina and/or trachea.
In the posterior mediastinum, neurogenic masses such as neuroblastomas or gangliomas are the most important tumors.
Foregut duplication cysts deriving from the esophagus or bronchus and even rare masses like lymphangiomas can be found.
What kind of mediastinal masses are diagnosed prenatally?
Cystic masses. These can be foregut duplication cysts, lymphangiomas and rarely neuroenteric cysts. Infrequently, fetal mediastinal teratomas can be diagnosed compromising the airway or presenting with pericardial effusion which can lead to fetal demise.
Parents need to be counselled before delivery.
A CT scan or MRI needs to be performed postnatally to plan surgery.
What is the role of the Ex Utero Intra Partum (EXIT) procedure in the management of prenatally diagnosed mediastinal mass?
Mediastinal teratomas can compress intrathoracic structures and present with non-immune fetal hydrops and/or respiratory distress in the newborn. EXIT allows to secure the airway after delivery. Planning an EXIT requires a thorough planning with a multidisciplinary team.
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The EXIT procedure has resulted in a high survival rate of fetuses with neck masses causing upper aerodigestive tract compression. The procedure was developed as a tool to manage a fetus with a congenital diaphragmatic hernia following a fetal tracheal occlusion procedure.
It allowed time to maintain the fetus on placental circulation while the occluding clip or balloon was removed, and airway patency was reestablished.
The EXIT procedure was subsequently found to be a versatile tool that can be used to manage a variety of fetal conditions, including giant cervical masses.
Prior to the EXIT procedure, a few cases of fetal intubation on placental circulation had already been reported in fetuses with cervical masses. This procedure was described under the acronym OOPS, operation on placental support. The term is no longer used and has been replaced by EXIT.
EXIT procedures require advanced multidisciplinary planning. Members of an EXIT team include maternal fetal medicine specialists, both pediatric and obstetrical anesthesiologists, pediatric surgeons and/or pediatric head and neck surgeons, and a pediatric cardiologist to continuously monitor cardiac output through a fetal echocardiogram. EXIT procedures should be carried out in centers with significant fetal and neonatal expertise. The procedure has undergone some refinements since first described.
Its major components include
1) pharmacologic uterine relaxation,
2) accurate placental mapping by ultrasound,
3) an efficient hysterotomy at least 5 cm away from the placental border performed using a special uterine stapler that decreases blood loss,
4) maintaining the fetus partially within the uterine cavity,
5) exposing only the relevant organs,
6) fetal intravenous access in order to directly administer anesthetic agents, and
7) direct monitoring of fetal cardiac function by echocardiography.
Uterine relaxation is induced using inhaled anesthetics, in addition to beta-adrenergic agonists if necessary.
A rapid flow fluid warmer helps maintain the uterine fluid volume and temperature.
If antegrade intubation of the trachea is not possible during an EXIT procedure, the trachea should be identified by dissection through the tumor and intubated retrograde.
A tracheostomy is not recommended, as it does not constitute a stable airway in these patients with massive cervical lesions, and it will also be within the field of dissection during tumor excision.
Survival rates of 60%–90% have been reported in cohorts of fetuses with giant cervical masses. Fetal demise may occur due to hydrops fetalis, severe polyhydramnios resulting in premature birth, or associated malformations.
Several fetal treatment centers have reported survival in the 75%–95% range after an EXIT procedure for a giant fetal cervical mass.
Mortality after an EXIT procedure is frequently due to pulmonary hypoplasia, which may affect up to 30% of these fetuses. This is thought to result from upward traction by the large cervical mass on the airway, compressing the lungs against the apex of the thorax.
Recent studies have investigated whether fetal lung volumes calculated using the MRI performed for evaluation of the mass may predict this complication. However, this has yet to be widely validated.
Long-term outcomes of patients with giant cervical masses appear to depend on the etiology of the mass. Patients with giant cervical lymphatic malformations are more likely to require multiple procedures and are at high risk for persistent disease, cranial nerve dysfunction, and moderate to severe disfigurement, compared to those with teratoma.
Some teratomas can result in mandibular hypoplasia and craniofacial deformities. However, long-term functional and cognitive outcomes are good in most patients.
From the maternal perspective, the EXIT procedure requires a general anesthetic during delivery, a longer delivery, and a potential for higher blood loss related to uterine relaxation.
The incidences of hemorrhage and infectious complications appear similar to that of conventional Caesarean section.
Unlike patients who undergo open maternal fetal surgery, uterine dehiscence is rare after an EXIT procedure. The ability to undergo an uncomplicated delivery in future pregnancies is preserved.
The choice of an EXIT procedure for the treatment of a giant cervical mass has also been analyzed in several studies.
Lymphatic malformations are less likely to result in esophageal and airway obstruction as they usually displace the upper aerodigestive tract, rather than compress it.
The prenatal diagnosis of teratoma and the presence of polyhydramnios have therefore been found to predict the need for an EXIT procedure.
More recently, a tracheoesophageal complex displacement index (TEDI) has been described. This index is calculated using MRI by adding the vertical and lateral distances between the tracheo-esophageal complex and the ventral border of the cervical spine.
A TEDI greater than 12 mm was found to be predictive of significant airway compromise requiring an EXIT procedure.
Sherif
How do mediastinal masses present? [1]
Many mediastinal masses are an incidental finding on chest radiographs and asymptomatic.
The most common symptoms at presentation are dyspnea, cough, fever, aching pain.
Children may also present with recurrent pulmonary infections.
Malignant tumors are most likely to be symptomatic with dyspnea, orthopnea and cough.
They are usually located in the anterior mediastinum.
Rarely, Horner ́s syndrome and superior vena cava syndrome are reported in relation with malignant lesions in the posterior or middle mediastinum.
Which mediastinal masses have a rapid versus slow/chronic onset?
A rapid onset of symptoms is suggestive for lymphoblastic non-Hodgkin’s lymphoma, an intermediate onset Hodgkin’s disease or mediastinal large cell non-Hodgkin’s lymphoma, and a chronic onset is typical for slow growing tumors such as teratoma.
In older patients, a mediastinal mass can develop in relation to malignant adenopathy deriving from a non-seminomatous germ cell tumor.
How does the diagnostic workup for a mediastinal mass look like? [1]
Imaging is the first step to accurately diagnose a mediastinal mass.
It should be guided by a well conducted clinical exam looking for palpable lymph nodes, Horner’s or superior vena cava syndrome, respiratory distress, wheezing or stri- dor consistent with a compression of the trachea.
Incidental findings are usually discovered on a chest x-ray done for repeated and chronic respiratory symptoms.
A CT scan needs to be performed to further workup the suspected diagnosis.
Posterior mediastinal cystic masses are very well described (bronchogenic cysts, intestinal duplications as well as neurogenic tumors).
For these cases MRI is use- ful to assess the extension to the intervertebral foramina.
In anterior mediastinal masses, multiple enlarged lymph nodes on CT are the most frequent additional finding.
FDG-PET/CT has become the modality of choice for staging most lymphomas and is more accurate in detecting both intranodal and extranodal disease than CT.
What are the typical radiologic features of a mediastinal teratomas on MRI?
A cystic or mixt cystic and solid lesion and containing fat, soft tissue and calcifications
Do all mediastinal masses require a biopsy?
No. A cystic lesion arising in the posterior mediastinum doesn’t need a needle or a surgical biopsy and primary surgical resection is indicated. For most of the other lesions, either posterior or anterior, a biopsy should be obtained to obtain a definite diagnosis.
Can it be dangerous to biopsy a mediastinal mass under general anesthesia?
Yes. The respiratory status of the patient need to be carefully assessed since the intra tracheal ventilation for general anesthesia can be difficult due to sudden airway and cardiovascular collapse.
Of note, signs and symptoms of airway compression and cardiovascular instability may be absent prior to anesthesia.
However, the possibility of life-threatening collapse of the airway or cardiovascular obstruction has to always be taken into consideration by both the surgeon and the anesthesiologist.
What are the alternatives to a direct biopsy under general anesthesia?
Whenever possible, an alternative biopsy site/specimen should be chosen and the tissue harvested under local anesthesia. This can be pleural effusion, peripheral blood smear for leukemia or Bone Marrow aspiration (BMA). If palpable lymph nodes are present, these may be easily removed and send for histology. Finally, if nothing but a biopsy under general anesthesia is doable, a mediastinoscopic biopsy should be considered as a safe technique in children.
What biological workup should be done for a mediastinal mass?
Cystic masses of the posterior mediastinum do not need any specific test. In con- trast, solid lesions require tests such as Vanillylmandelic Acid, Homovanillic Acid, and Catecholamines in a urine sample. In case of an anterior mediastinal mass, α-FP and HCG for suspected teratomas. If the diagnosis is in favor of hematologic disease LDH, blood formula, peripheral blood smear or BMA should be obtained.
The three mediastinal compartments are shown diagrammatically in Figure 23.1. Which of the subsequent options describes the correct association between zone and pathology?
A Zone 1: ganglioneuromas
B Zone 1: foregut cysts and duplications
C Zone 2: teratomas
D Zone 3: thymic cysts
E Zone 3: neuroblastomas
E
The anterior mediastinum (Zone 1) is bounded by the posterior surface of the sternum, the thoracic inlet, and the anterior surface of the great vessels, heart and pericardium.
The middle mediastinum (Zone 2) extends to the anterior border of the vertebrae.
The posterior mediastinum (Zone 3) is the area posterior to the anterior border of the vertebrae.
A thorough understanding of the anatomy and embryology of the mediastinum is important for the surgeon when evaluating, planning, diagnosing and operating on patients.
Conditions that can present within Zone 1 include teratoma, thymic hyperplasia, thymic cysts, non-Hodgkin’s lymphoma, Hodgkin’s lymphoma and lymphangioma.
In Zone 2, non-Hodgkin’s lymphoma, Hodgkin’s lymphoma, lymphangioma and foregut cysts and duplications can be seen.
Similarly the conditions that can develop within Zone 3 include ganglioneuroma and neuroblastoma.
SPSE 1
What is the most common cause of the mass seen in Figure 23.3?
A neuraoenteric cyst
B lymphatic malformation
C neuroblastoma/ganglioneuroma
D oesophageal duplication cyst
E bronchogenic cyst
C
The most common masses in the posterior mediastinum are ganglioneuromas and neuroblastomas. (Approximately 20% of ganglioneuromas and neuroblastomas present in the chest.) Because of their benign behaviour, the outlook is significantly better than neuroblastomas presenting in the abdomen. Anterior thoracic meningoceles are rare lesions associated with severe vertebral abnormalities; they are progressive in size and symptoms. They typically present with weakness that progresses to paraplegia and require operative correction. The other rare lesion in this region is the neuroenteric cyst; these connect the central nervous system and the gastrointestinal tract. They occur embryologically as a result of failure of separation of the primitive neural tube and foregut. The lesions typically have well-differentiated muscular layers with intestinal mucosal lining, typically gastric. They are optimally imaged using MRI.
SPSE 1
What is the most common cause of the lesion seen in Figure 23.4?
A neuroenteric cyst
B lymphatic malformation
C neuroblastoma/ganglioneuroma
D foregut duplication cyst
E sarcoma
D
Foregut duplication cysts: oesophageal duplication cysts and bronchogenic cysts. oesophageal duplication cysts are usually found arising within the oesophageal wall near the carina.
There is a great deal of variation in the location of these cysts.
They share the muscular layer with the oesophagus and often have a respiratory epithelial lining, sometimes with rudiments of cartilage.
Bronchogenic cysts are lined by respiratory epithelium.
These lesions are most commonly discovered in asymptomatic patients who have a chest X-ray done for other reasons.
The CT scan is best for delineating the extent and location of these lesions.
Treatment consists of excision, if possible. more-peripheral lesions can be resected completely; central lesions often share a common wall with the underlying structure and require careful planning prior to surgery.
SPSE 1
A 13-year-old girl is referred with a mass as shown in Figure 23.5. What is the most likely diagnosis?
A lymphoma
B thymic cyst
C teratoma (germ cell tumour)
D duplication cyst
E neuroblastoma
C
Primitive germ cell tumours may occur in the mediastinum: these include the general categories of tumours arising from pure extraembryonic tissues (seminoma, embryonal carcinoma, yolk sac tumour or choriocarcinoma), which are very rare, or of embryonic tumours (teratomas) containing tissues for all three embryonic cell lines (ectoderm, endoderm and mesoderm), which are uncommon but comprise roughly 16% of all tumours in this region.
However, teratomas are the only tumour with a solid or circumscribed morphology. They arise from thymus or pericardial tissues.
Depending on their location, they may be asymptomatic (detected on a chest X-ray done for other reasons (most common), vascular effects, airway compression, or specific hormonal effects.
SPSE 1
The lesion in Figure 23.6 has developed in a 5-year-old female, 2 years after resection of a cervical cystic hygroma. She has intermittent shortness of breath, with exertion, but is otherwise well. What would your treatment strategy be?
A embolisation
B cautious resection
C sclerotherapy: OK-432 or bleomycin injection
D interferon-2α therapy
E steroid therapy followed by vincristine if necessary
B
Cystic hygromas are progressive in some cases. The mixed nature of this lesion may suggest it might respond to sclerotherapy, but with this there is the risk of increased swelling in the injected cysts, which in this case, may worsen the respiratory compromise. Cautious resection is indicated, with meticulous attention to preserving any vital neuronal or vascular structures.
SPSE 1
