“EVALUATION OF MEDIASTINAL MASSES USING MULTI-DETECTOR COMPUTED TOMOGRAPHY WITH HISTOLOGICAL CORRELATION”
Dr.Shivanand Melkundi, Dr. Girish Desai, Dr. MeghnaRathod
M.R.Medical College, Gulbarga
ABSTRACT:
AIMS AND OBJECTIVES:
The objectives of the study are to categorise distribution of masses according to the mediastinal compartments, their characteristics on plain and contrast enhanced CT with histopathological correlation.
MATERIALS AND METHODS
The study was performed in 30 patients referred from department of medicine, surgery, paediatrics and TB & Chest, to the Department of Radiology, BTGH, Gulbarga in a period of 1 year with suspected case of mediastinal mass on chest radiography
All the subjects were subjected to plain and contrast enhanced CT scan.
RESULTS:
In our study, anterior mediastinum was the most commonly involved compartment, followed by superior mediastinum, posterior mediastinum and middle mediastinum.
Lymphoma is the most common lesion in anterior mediastinum and superior mediastinum, teratoma in middle mediastinum and Schwannoma in posterior mediastinum.
In our study, isolated compartmental involvement is common in posterior mediastinum followed by superior, middle and anterior mediastinum, however anterior mediastinum is most commonly involved in trans-compartmental lesions therefore anterior mediastinum was collectively the most common compartment involved followed by superior, posterior and middle mediastinum.
In the study lymphoma 37.5 %, Lymphoma and thymic masses 31.25%, Ca esophagus and Schwannoma were the most common masses in the anterior, superior, middle and posterior mediastinum resp.
CONCLUSION:
From the above results, we conclude that CT definitely played a major role in the evaluation of mediastinal mass regarding the compartmental distribution, mass effect upon adjacent structure and provisional diagnosis
Keywords: Mediastinum, Computed Tomography
INTRODUCTION:
Mediastinal masses represent a wide diversity of disease state. The clinical
spectrum of mediastinal masses can range from being asymptomatic to producing
compressive symptoms. Mediastinal masses span a wide histopathological and radiological
spectrum. The location and composition of a mass is critical to narrowing the differential
diagnosis. Although many of these masses have similar imaging appearances, clinical history,
anatomical position and certain details seen at imaging allow correct diagnosis in many
cases.
Chest radiography is a very common examination in clinical practice. Many
mediastinal reflections can be appreciated at conventional radiography (CR), and their
presence or distortion is the key to the interpretation of mediastinal abnormalities.
However, computed tomography (CT) is the most important tool in the evaluation of
amediastinal mass in determining the exact location as well as its relationship to adjacent
structures. Characterisation on CT is based on specific attenuation of air, fat, water and
calcium. High-resolution multiplanar reformation images display the detailed anatomical
relationship of the tumour with the adjacent structures.
An excellent soft tissue contrast also designates magnetic resonance imaging
(MRI) as an ideal tool to evaluate tumours of the mediastinum. Assessment of preoperative
relationships with the pericardium, heart cavities, spinal cord and vascular involvement is a
common indication.
Advantages of CT such as better spatial resolutions, shorter imaging time, less
expensive and its availability made CT a better imaging technique. Co-existing lung
abnormalities and calcifications within the lesions are better appreciated on CT.
CT guided biopsies can be performed with CT apart from evaluating the
mediastinal mass accurately.
AIMS AND OBJECTIVES:
- To study the distribution of mediastinal masses.
- To study the computed tomographic characteristics of mediastinalmasses.
- To study the involvement of neighbouring structures by mediastinalmasses.
- To compare CT findings with pathological findings and/or USG/MRI findings whereverpossible.
MATERIALS AND METHODS:
Source of Data: The main source of data for the study is patients from Basaveshwara Teaching and General hospital attached to Mahadevappa Rampure Medical College, Gulbarga, over a period of 1 year.
Method of Collection of Data: All patients referred from department of medicine, surgery, paediatrics and TB & chest, to the department of radio-diagnosis with the clinically suspected cases of mediastinal masses or who had a chest radiograph with suspicion of mediastinal abnormality.
Thorough clinical history and clinical examination is done before CT examination.
All the cases taken up for the study are evaluated using Philips Brilliance 6-Slice CT Scanner for the distribution, CT features and also the involvement of adjacent structures. Biopsy of the masses taken wherever possible.
Sample size: 30
Sampling Technique: Purposive sampling technique.
Type of study: Diagnostic Study/ Comparative Study.
Inclusion Criteria: CT study of mediastinum are conducted in:
1. Clinically suspected cases of mediastinal mass/lesion.
2. Patients where the chest radiograph showed the mediastinal mass
Exclusion criteria:
1. Cardiac cases
2. Traumatic cases.
OBSERVATION AND RESULTS:
Of the 30 cases in our study, most common presentation was in age group 3rd-6thdecade(56.6 %) with male preponderance(76.7%). Most of the patiemts came with chief complaints of cough(80 %) followed by dyspnoea(53.3%), chest pain(23.3 %) and fever(16.6 %).
Compartmental distribution of mediastinal lesions:
In our study, anterior mediastinum was the most commonly involved compartment, followed by superior mediastinum, posterior mediastinum and middle mediastinum.
In our study, isolated compartmental involvement is common in posterior mediastinum
followed by superior , middle and anterior mediastinum . However the anterior mediastinal is
most commonly involved in trans-compartmental lesions. Therefore anterior mediastinum was
collectively the most common compartment involved, followed by superior mediastinum ,
posterior mediastinum and middle mediastinum .
Lymphoma was the most common superior mediastinallesion(31.25%) followed by thymic carcinoma(18.7%) while the most common anterior mediastinal lesion was lymphoma(37.65%) followed by Ca. lung with MLN(18.7%).
Ca. esophagus and teratoma(40%) shared the most common etiology in middle mediastinum.
Schwannoma was found to be the most common lesion in posterior mediastinum in our study.
CT characteristics of the lesion:
70 % of the lesions were well defined while 30 % were ill defined.
Of 30 cases, 26 cases(86.7%) were hypodense on non contrast CT scan, remaining were iso dense and none of the cases showed hyperdensity on CT.
On contrast study: maximum of 26 cases(86.7%) showed moderate enhancement while remaining 4(13.3%) showed mild enhancement. None of the case showed intense/gross enhancement on post contrast study. Of the cases taking enhancement 25 cases(83.3%) showed heterogeneous enhancement while remaining 5(16.7%) showed homogeneous contrast uptake.
70 % of the cases showed mass effect over adjoining structures while 30% dint show any mass effect over surrounding structures.
DISCUSSION:
Computed tomography imaging techniques have contributed significantly tothe detection, characterization and staging of mediastinal masses.
The initial detection of mediastinal masses can be achieved mainly by chestradiograph (Frontal and Lateral views) and once found,they can be localized, furthercharacterized and staged by CT. However the main objective is to determine if thelesion is malignant or benign, as accordingly the further management depends.
According to the Davis et al[1]study in 400 consecutive patients withmediastinal masses, chest pain constituted the most common symptom i.e. 30%,followed by fever 20%.
Felsonin 1978 in a series of 550 cases reported, there is no predilection forthe masses to occur in the anterior mediastinum. But he reported more number ofcases being seen in the anterior mediastinum followed by posterior and middlemediastinum[2].
In our study, isolated compartmental involvement is common inposterior mediastinum (n=7, 23.4%) followed by superior (n=4, 13.3%) middle (n=4,13.3%) and anterior mediastinum (n=3, 10%). However the anterior mediastinal ismost commonly involved in trans-compartmental lesions (n=12, 40% and n=2, 6.7%).Therefore anterior mediastinum (n=17, 56.7%) was collectively the most commoncompartment involved, followed by superior mediastinum (n=16, 53.3%), posteriormediastinum (n=9, 30.1%) and middle mediastinum (n=6, 20.0%).
Our study is similar to the study conducted by Strollo et a1[33]in 1997 whereinanterior mediastinum constituted 50% of the masses.
In our study, Lymph nodal masses formed majority of the cases with 30% andLymphoma (66.7%) being most common lymph nodal mass. Thymus lesions forms16.7% of the cases and Thymoma being most common thymic mass. Neural tumorsforms 16.7% of the cases and Schwannoma being most common neural tumor.
In the similar studies conducted by Cohen et al [4]and Davis et al[1]foundthymic lesions as common mediastinal lesions. In a study by Chen et al[5]on 34patients with CT diagnosis of thymic mass, thymoma constituted 91 %, thymic cyst2.9%. Whereas in our study, of the 5 patients with thymic mass, thymoma constituted60% and thymic carcinoma constitute 40%.
According to Naidich et al [6], Thymomais most commonly seen between 50-60 years which is comparable to our study inwhich the 3 patients with thymoma where of age 44, 62 and 63 years respectively.
Anterior Mediastinal masses:
a. Thymic hyperplasia
Most commonly associated with myasthenia gravis, it is also seen in otherconditions such as thyrotoxicosis, autoimmune diseases like Hashimoto’s thyroiditis,Addison’s disease, HemolyticAnemia and Behcet’sdisease.The thymus may atrophydue to stress or consequence of steroid or anti neoplastic drug therapy. [7, 8, 9]Thegland returns to its original position on recovery or cessation of treatment, or maybecome larger than its previous normal size, in the phenomenon known as “ReboundThymic Hyperplasia”.
b. Thymoma:
Most common primary tumor of the anterior mediastinum, it accounts for 15%of primary mediastinal mass [6]. These are neoplasms originating from the thymicepithelium and are most common during 5th to 6th decade.
On CT, thymomas appear as homogenous soft tissue density masses, which are usually sharply demarcated and oval, round or lobulated in shape, project to one side of the mediastinum, and do not conform to the normal shape of the thymus.Thymomas usually enhance homogenously. Large tumors have areas of hemorrhage, necrosis or cyst formation.
Staging of thymoma:
Stage I: Intact capsule
Stage II: Invasion of adjacent fat only
Stage III: Invasion into other mediastinal structures, lung and pleura
c. Thymic Carcinoma:
Arises from thymic epithelial cells and accounts for about 20% of thymic epithelial tumors[10]. Age of incidence is around 50 years.Thymic carcinoma cannot be distinguished from thymoma on CT unless enlarged lymph nodes are visible in the mediastinum or distant metastases are evident.
On CT, it is seen as homogenous soft tissue mass or heterogeneous with areas of cystic necrosis. Calcification is seen in 10-40% of cases. Obliteration of fat planes and extension into pericardium and pleura is usually seen [11].
d. Thymolipoma:
It is a rare, benign well encapsulated thymictumor, consisting primarily of mature adipose tissue and variable amounts of thymic tissue. It can arise within the thymus or be connected to the thymus by a pedicle. It is most commonly seen in the children and young adults. CT shows a fatty mass with varying amounts of intermixed soft tissue representing thymic tissue.On MRI, fatty component shows high signal on T1W with soft tissues having intermediate signal intensity.
e.Teratoma:-
They contain elements of all germinal layers. Teratomas are classified as mature, immature and malignant [3].Mature teratomas are common accounting for 70% of germ cell tumors in childhood and 60% of mediastinal germ cell tumors in adult.CT often shows combination of fluid filled cysts, fat, soft tissue and areas of calcification. Calcification seen in 20% to 80% of cases, it may be focal, rim like, or rarely representing teeth or bone. A fat fluid level is particularly diagnostic.[12]
f. Thyroid masses:
Mediastinal involvement by thyroid masses is most often anterior and is due to down ward extension of either a multi nodular colloid goiter, or occasionally an adenoid or carcinoma.Rounded or irregular, well defined areas of calcification may be seen in benign areas, whereas amorphous cloud like calcification is occasionally seen within carcinomas.[8]CT is at greatest value in defining the
morphologic extent.
g.Primary Mediastinal Lymphoma:
It constitutes about 20% of all mediastinalneoplasms in adult and 50% in children [13]. A mediastinal mass is also a frequent manifestation of lymphoma. The most common cause for such primary disease are Hodgkin's disease, large cell lymphoma and b-lymphoblastic lymphoma.Hodgkin’s
Lymphoma is a more common cause and occurs in older group (Median age 55years). [6]The typical presentation consists of an anterior mediastinal mass often associated with enlarged nodes in the middle and posterior mediastinum and hila.
On CT Hodgkin's lymphoma is characterized by the presence of a discrete anterior superior mediastinal mass with surface lobulations. Surface lobulations of main mass is due to involvement of multiple nodes and coalescence. Masses typically exhibit homogenous soft tissue attenuation, while large tumours may exhibit heterogeneity with complex low attenuation representing necrosis, hemorrhage and cystic degeneration. It commonly involves cervical, mediastinal, hilar and Para aortic nodes [14].
Non-Hodgkin’s lymphoma comprises of mediastinal large 8-cell lymphoma and lymphoblastic lymphoma and is more common in children than Hodgkin's lymphoma.
Large cell lymphomas are typically confined to the mediastinum and contiguous nodal areas initially without showing extrathoracic disease at presentation. It may present with hematogenous spread to kidney, liver, ovary, adrenal gland, GI tract and central nervous system during disease progression or at recurrence. CT demonstrates mediastinal mass without surface lobulations, often associated with
vascular involvement and pleural or pericardial effusion.
Lymphoblastic lymphoma is characterized by mass without surface lobulations involving vascular structures often associated with pleural or pericardial effusion. Systemic involvement is in the form of involving cervical, axillary, paraaortic, mesenteric and inguinal nodes and by hepatomegaly and splenomegaly.[15]
MIDDLE MEDIASTINAL MASSES:
a.Foregut duplication cysts:
It includes bronchogenic, neuroenteric and oesophageal duplication cysts
Bronchogenic cyst:
Bronchogenic cysts are congenital lesions thought to result from abnormal budding of the embryonic foregut. Most cysts are located in the mediastinum, near the tracheal carina predominantly in the middle mediastinum (79%) less commonly may occur within the lung parenchyma, pleura or diaphragm (15%) according to McAdam's series [16].CT typically shows sharply marginated thin walled mediastinal mass of homogenous soft tissue or water attenuation. Rarely, calcification of the cyst wall is present. When dense, bronchogenic cysts may be difficult to distinguish from solid lesions. An important clue can be their lack of enhancement following contrast administration. [17]
Neuroenteric cysts:
These rare lesions are connected to the meninges through a midline defect in one or more vertebral bodies and are composed of both neural and gastrointestinal elements. A connection with the esophagus is often present. CT appearance is same as that of other duplication cyst, but the presence of vertebral abnormality points to the diagnosis, vertebral anomalies are present in half of the cases.
Oesophageal duplication cysts:
They are lined by gastrointestinal tract mucosa and are often connected to the esophagus. 60% are found in the lower posterior mediastinum, adjacent to the oesophagus, and are sometimes found within its wall. On CT it is indistinguishable from bronchogenic cyst except for the location [18].
POSTERIOR MEDIASTINAL MASSES:
- Neurogenic Tumours:
They account for about 9% of primary mediastinal masses in adults, althoughthey are more prevalent in children, constituting 29% of mediastinaltumours[19].
Tumours are divided as follows:
- Nerve sheath tumours: Neurofibromas, Schwannoma, Malignant peripheral nerve sheath tumours, Neurofibrosarcoma.
- Ganglion cell tumours: Ganglioneuroma, Ganglioneuroblastoma, Neuroblastoma.
- Paragangliomas: Chemodectomas - Aortic body tumour, Sympathetic chain
tumours, Pheochromocytoma.
Nerve Sheath Tumors:
The Schwannoma is the most common intra thoracic nerve sheath tumour. In their classic form, they are eccentric and encapsulated and have no nerve fibers. Almost all intra thoracic nerve sheath tumours arise either from the intercostals, or the sympathetic nerves, the rare exception being Neurofibromas or Schwannoma of the phrenic or vagus nerves. Many arise close to the spine and may extend through the neural exit foramina into the spinal canal the so-called "Dumb bell tumour". Nerve sheath tumours are rare in patients below age 20 and virtually nonexistent in patients who are less than 10 years old except in patients with neurofibromatosis [20].
Ganglion cell tumours:
Ganglion cell tumours form a spectrum with Neuroblastoma at the malignant end and Ganglioneuroma at the benign end, Ganglioneuroblastoma being an intermediate form.The mediastinum is the second most common primary site after the adrenal gland. Primary mediastinalneuroblastoma appears to have a better prognosis than those that arise primarily in the abdomen. Neuroblastoma and ganglioneuroblastoma are essentially tumours of childhood, fewer than 10% seen
in patients older than 20 years of age. Ganglioneuroma is seen in age range of 1 to 50 years.
At CT, many neural tumours have mixed density, including low attenuation region. On non-contrast enhanced CT, Schwannoma often demonstrate lowerattenuation than skeletal muscle because of their high lipid content, interstitial fluidand areas of cystic degeneration. Neurofibromas are often more homogenous andshow higher attenuation than schwannomas because they have fewer of these
histologic features.Nerve sheath tumours calcify only occasionally. These lesions may heterogeneously enhance following contrastadministration.
Ganglion cell tumours arise slight more anteriorly with their epicenter against thevertebral body, whereas nerve sheath tumours are centered on the exit foramina,or are plastered against the chest wall.Calcification may be seen in all types of neural tumours. In neuroblastoma thecalcification is usually finely stippled, whereas Inganglioneuroblastoma andganglioneuroma, it is denser and coarser occurring most frequently in the largerbenign lesions.
Mediastinal Paragangliomas:
They are rare, forms only 2% approximately.[21]One third of mediastinalpheochromocytomas are non-functioning and asymptomatic, the remainder present with symptoms, signs and laboratory findings of catecholamine overproduction.
On CT, the lesions arerounded soft tissue masses which are usually extremely vascular andtherefore enhance brightly. MRI is particularly advantageous in intracardiacpheochromocytomas.
- Tuberculous paravertebral lesions:
The vertebral column is the most common site of osseous tuberculousinvolvement comprising in most series about 50% of cases. The lower dorsal andupper lumbar vertebrae are most frequently affected. The spread of tuberculosis of thespine is usually by hematogenous route by perivertebral arterial or venous plexus, orrarely by extension form a paraspinal infection. CT scan is excellent for visualization of end plate destruction, fragmentation of the vertebrae, and paravertebral calcifications. Inflammatory collections and masses are best seen after the contrast administration. Small necrotic foci are recognized by CT scans and they are difficult to find in the radiographs i.e. foci less than 1.5 cm in diameter are not demonstrable in a conventional radiograph. Extension