ABSTRACT

CORRESPONDING AUTHOR:
P. S. S. Kiran,
Department of Radiodiagnosis,
KIMS Medical College,
Amalapuram- 533201.
E-mail: drpsskiran@gmail.com
Ph: 0091 9490119999

ABSTRACT: AIM: Our  objective of study was to characterize the mediastinal lesions on plain and contrast  enhanced  computed  tomography, the  distribution  of  mediastinal masses, the nature of the lesion, enhancement pattern, presence of calcifications and presence of mass effect, the involvement of structures and to compare computed tomography  findings with pathological diagnosis wherever possible. The study was performed from August 2012 to February 2013 in the Department of Radio-diagnosis Konaseema Institute  of Medical Sciences, Amalapuram, AP on 50 cases with mediastinal pathology which were initially detected on chest radiographs. The maximum number of cases occurred in 4th - 6th decade.
In our study of 50 cases of mediastinal masses, the anterior mediastinum was the most common compartment to be involved with (52% ) followed by posterior mediastinum (30%) and middle mediastinum (18%).
KEY WORDS: - Computed tomography, Anterior Mediastinum, Middle Mediastinum, Posterior Mediastinum

INTRODUCTION: Computed tomography plays a significant role in the assessment of various mediastinal pathology which were initially detected on the chest radiographs. The maximum number of cases occurred in 4th-6th decade. Mediastinal masses occurred commonly in males. In our study of 50 cases of mediastinal masses, the anterior mediastinum was the most common compartment to be involved (52%) followed by posterior mediastinum (30%) and middle mediastinum (18%).
Thymic masses (26.9%), neural tumors (33.6%) and metastatic lymph node masses (44.5%) were the most common mediastinal masses in the anterior, posterior and middle mediastinal compartments respectively.
In the pediatric age group neurogenic tumour was the most common mediastinal mass. Calcification was noted in (24 %) of cases. Mass effect upon the adjacent mediastinal structures was observed in (62 %) of the cases and was predominantly noted upon the airways.
Forty three cases (86%) were histologically verified and four cases (8%) of aortic disorders were verified with conventional angiography. Totally 43 cases were verified with histopathology and angiography. With an accuracy of (94%) forty three cases CT is highly useful modality for investigation of mediastinal masses.

MATERIALS AND METHODS: The study was performed from  August 2012 to February 2013 in the Department of Radio-diagnosis  Konaseema Institute  of Medical Sciences, Amalapuram, AP. Patients referred  from  Medicine,  Surgery  and  Paediatrics  were  evaluated  through detailed history, necessary physical examination and computed tomography was carried out using Double slice CT scan - GE. Scans were obtained with  both  Plain and Contrast  study.
We classified our mediastinal lesions into three categories as anterior, middle and posterior mediastinal masses.

RESULTS: Our study included 50 cases of mediastinal lesions between age groups 6-76 years. The maximum number of cases occurred in 4th - 6th decade. In our study of 50 cases of mediastinal masses, the anterior mediastinum was the most common compartment to be involved with (52%)  followed by posterior mediastinum (30%) and middle mediastinum (18%).

DISCUSSION: The mediastinum is a site for vast range of diseases varying considerably, ranging from tumors both benign and malignant, cysts, vascular lesions, lymph node masses and mediastinitis. Although conventional radiographs can show recognizable abnormalities in many  patients  with   mediastinal  abnormalities,  in patients  with  mediastinal pathology radiographs are limited in their sensitivity to delineate the extent of mediastinal  abnormalities  and  the  relationship  of   masses  to  specific  mediastinal structures. With computed tomography these problems are overcome because of its excellent resolution and tomographic format and therefore CT plays an important role in the evaluation of the mediastinum.
Majority of the symptoms were of non-specific nature like cough, chest pain, fever, dysphagia etc. These symptoms were mainly due to mass effect from the mediastinal lesions and were dependent on the location of the mass. Anterior mediastinal masses mostly presented with cough and dyspnea probably due to tracheal compression. Middle mediastinal  lesions  due  to  their  location  presented  with dysphagia  due  to  involvement of the esophagus or its compression. Neurogenic tumours account for about (9%)of primary mediastinal masses in adults, although they are more prevalent in children, constituting  (29% )of mediastinal tumours. 6
In our study, anterior mediastinal masses were found to be the commonest accounting for (52 %). Posterior mediastinal masses accounted for (36%), followed by middle mediastinal masses accounting for (20%) of the cases. The cases were analyzed in the following manner as discussed below:

A: Symptoms Distribution

In our study of 52 cases, cough was the most common clinical symptom constituting (44 %) followed by dyspnea (36%), fever (20%) and chest pain (20%).

According   to  the  Davis   study   in  400  consecutive   patients   with mediastinal  masses,  chest  pain  constituted  the  most  common  symptom  i.e.  (30%), followed by fever (20%). ⁸

B: Compartmental distribution of mediastinal masses

In our study of 52 cases, the majority  of the mediastinum masses were in the anterior mediastinum constituting ( 52%) followed  by middle and posterior  mediastinal  compartment  which  is  similar  to  the  study  conducted  by Strollo in 1997 wherein anterior  mediastinum constituted  (50% )of the masses.^7,13

C: Individual masses distribution (Based on the tissue of origin).

In our study Lymphoma constituted (6%) of the mediastinal masses which is similar to study conducted by Wychulis .¹

Lymph nodes having a short axis of 2cm or more often reflect the presence of neoplasm, such as metastatic tumor or lymphoma, sarcoidosis or infection and should always be treated as potentially significant. Whereas in variety of non infectious and non-granulomatous inflammatory diseases they are usually smaller than 2cms .^2,3,4   

Malignant lesions have predominated in the male population while benign lesions have occurred with equal frequency in both. Majority of the benign lesions have occurred in between the 2nd and 4th decade. In case of malignancy, majority of the cases have occurred between 4^th and 6th decade.

Lymphoblastic  lymphoma  is  characterized  by  mass  without  surface  lobulation involving  vascular structures often associated with pleural or pericardial effusion, by systemic  nodal   involvement  including  cervical,  axillary,  paraaortic  mesenteric  and inguinal and by hepatomegaly and splenomegaly.¹⁹

TUBERCULOUS LESIONS: In our  study,  tuberculous lesions  constituted ( 16%),  which  is  greater  in  comparison  to Wychulis study (i.e. 6.3%) probably due to higher prevalence of tuberculosis in comparison to the western  population.¹ Our study had 3 cases of paravertebral abscess (5.6%) which was associated with vertebral body destruction.

According to Im study, right paratracheal lymph node enlargement was seen in( 87%) of cases whereas our study showed( 60 %) involvement. Similarly in Im study 52% of the lymph node enlargement showed central areas of low attenuation with rim enhancement on contrast study.¹¹ Our study showed (40 %) involvement.

According to Choyke in their study on adult onset pulmonary tuberculosis, reported (40%) of adults showed presence of pleural effusion, whereas our study showed

(50 %) cases of Tuberculosis associated with pleural effusion.¹²

Hilar and mediastinal lymph node enlargement is commonly seen on CT in active tuberculosis   cases, more frequently   in children than adults. ⁶ 

THYMIC MASSES: Computed tomography should be the imaging method of choice following plain chest radiograph when suspected thymic abnormality require further evaluation. ⁵ In  our  study  the  thymic  tumors  formed  the  majority  with  (14%)  which  is similar to  studies  conducted  by Cohen and Davis .^10,8 In a study by Chen on 34 patients with CT diagnosis of thymic mass, thymoma constituted( 91  %),  thymic  cyst ( 2.9%) whereas  our  study  of  7  patients  with  thymic  mass, thymoma constituted( 42%), and thymic hyperplasia (28 %).⁹

According to Naidich, Thymoma is most commonly seen between 50- 60 years which is comparable to our study in which the 3 patients with thymoma where of age 40, 48 years and 48 years respectively.¹⁵

THYROID MASSES: Intrathoracic goiters are a common cause of mediastinal enlargement. Thyroid masses account for 11-15 % of mediastinal masses.¹⁴ In our study they represented only (3%) of the cases. Rounded or irregular, well defined areas of calcification may be seen in benign areas, whereas amorphous cloud like calcification is occasionally seen within  carcinomas.²⁰            

ANEURYSM  OF THORACIC AORTA: Aortic  aneurysms  can  result  in  a  mass  in  the  anterior,  middle  or  posterior mediastinum. The classical description of aortic aneurysm is an area of permanent dilatation of the aorta where the dilatation is at least 50% greater than baseline or standardized normal limits.¹⁶

PLEUROPERICARDIAL CYST: They result from aberrations in the formation of coelomic cavities. Pericardial cysts are invariably connected to the pericardium. Majority of them arise in the anterior cardiophrenic angle, more frequently on the right, but can be seen as high as the pericardial recesses at the level of the proximal aorta and pulmonary arteries .¹⁷ CT shows thin walled unilocular water density (O-20HU) cystic structure. Wall may calcify.

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.¹⁸

CLASSIFICATION OF MEDIASTINAL MASSES- Based on Location ²¹

Compartmental distribution of mediastinal lesions

Anterior Mediastinal Lesions distribution

Middle mediastinal Lesions distribution

Posterior mediastinal lesions distribution

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Compartmental distribution of mediastinal lesions

FIGURE 1- CECT showing lobulated anterior    FIGURE 2- CECT showing anterior mediastinal

 mediastinal mass with mixed attenuation.              mass with  fat density and some areas of

--THYMOMA                                                                 inhomogeneous soft tissudensity.THYMOLIPOMA

FIGURE 3-CECT showinh left hilar                              FIGURE 4- CECT showing poorly

mass with moderate heterogenous                        enhancing homogenous, soft-tissue

enhancement.---Carcinoma lung with             attenuation mass in left paravertebral region.----           

mediastinal lymphadenopathy                                    .----NEUROGENIC TUMOUR

 FIGURE 5- CECT showing cystic right             FIGURE 6- CECT showing lobulated heterogenously

anterior mediastinal mass with peripheral           enhancing anterior mediastinal mass

rim enhancement.----THYMIC CYST                           on right side.--HODGKINS LYMPHOMA

FIGURE 7-CECT showing central necrotic             FIGURE 8—CECT showing aneurysm of

areas with rim enhancing lesions in middle             arch of aorta

mediastinum.—TUBERCULAR

 LYMPHADENOPATHY

    Metastatic lymphadenopathy                               TB spine with paravertebral abscess