Lymphoma represents one of the most common tumors in mediastinum approximately 10–15% of all masses [18, 19].
DWI is functional MR imaging technique with no need for special preparation, contrast injection or radiation exposure and allows the analysis of tissue characteristics based on the diffusivity of water molecules within tissues .
With the recent technology and advances in MR systems, diffusion weighted MRI (DWI MRI) of the chest is emerging as a promising fast technique that minimizes the effect of physiological motion artifacts that arise from respiration and cardiac movement .
The main purpose of this cross-sectional study was to assess the implementation of diffusion MRI in the algorithm of diagnosis of mediastinal lymphoma and assessment of post therapeutic response.
This study involved reviewing the DWI MRI finding results of 32 patients that were referred from the clinical oncology department for MRI assessment; all the patients were pathologically proved cases of lymphoma. Patients were grouped according to their histopathology and treatment status.
Out of 32 patients, 22 patients were diagnosed as Hodgkin lymphoma (68.75%) and 10 patients were diagnosed as non-Hodgkin lymphoma (31.25%).
Out of 32 patients, MRI was done to 18 patients before starting treatment; 12 patients were diagnosed as Hodgkin lymphoma (66.66%), and six patients were diagnosed as non-Hodgkin lymphoma (33.33%). ADC range was 0.476 to 1.4.
There is statistic significant difference between ADC values in LN (p = 0.003) and mediastinal masses (p = 0.046) in Hodgkin and non-Hodgkin lymphomas.
In agreement with Broncano et al.  and Çakmak et al.  who stated that, MRI DWI can be used as a reliable non-invasive technique that can differentiate between benign and malignant tumors including those of the mediastinum. This also consistent with Sabri et al.  and Abou Youssef et al.  who stated that the ADC values of malignant mediastinal lesions are significantly lower than those of benign lesions and determined cut-off ADC values to differentiate the two.
ADC range in non-treated Hodgkin lymphoma cases presented with lymph node presentation was 0.83 to 1.4 with ADC average 1.1072, while ADC range in cases presented with masses was 0.774 to 1.1 with average 0.939. The ADC range in non-treated non-Hodgkin lymphoma cases presented with lymph node presentation was 0.476 to 0.548 with ADC average 0.512, while ADC range in cases presented with masses was 0.507 to 0.668 with average 0.5946. ADC cut off value to differentiate Hodgkin from non-Hodgkin lymphoma in lymph nodes was 0.72 (p = 0.003), while ADC cut off value to differentiate Hodgkin from non-Hodgkin lymphoma in mediastinal mass was 0.38 (p = 0.046).
On other hand Razek et al.  and Sabri et al. , stated regarding the pathological subtypes of mediastinal lymphoma, that there were no statistically difference between the ADC average value of Hodgkin lymphoma and non-Hodgkin lymphoma in these studies but the ADC value of non-Hodgkin lymphoma was lower than Hodgkin lymphoma. These findings may be attributed to limited study on relatively small sample size.
In this study out of 18 patients who did not start treatment at time of study eleven (61.1%) cases presented by mediastinal masses and seven (38.9%) cases present by lymph nodes. On searching the literature, no attempts to differentiate between lymphoma presentation as masses or discrete lymph nodes, in particular were found.
All of the eleven cases with mediastinal masses had the epicenter of the mass in the anterior mediastinum; which agrees with Shahrazad et al.  who stated that mediastinal lymphoma usually occur in the anterior mediastinum.
In the non-treated group of Hodgkin cases presented by discrete and partially amalgamated lymph nodes, the distribution of lymph nodes was as follows: Enlarged para-tracheal lymph node were in five cases (19%), enlarged prevascular lymph nodes were in four cases (15%), enlarged para-aortic lymph nodes were in two cases (8%), enlarged sub-aortic lymph nodes were in three cases (11.5%), enlarged hilar lymph nodes were three cases (11.5%), enlarged subcarinal lymph nodes were in two cases(8%). Enlarged para-esophageal lymph nodes were in four cases (15%), enlarged cardio-phrenic was in one case (4%).enlarged supra clavicular lymph nodes was in one case (4%) and enlarged internal mammary lymph nodes was in one case (4%).
That is consistent with Mehrian et al.  study on patients with Hodgkin’s disease, enlarged lymph nodes were distributed mainly in the following zones: 4 (lower paratracheal; 89.2%), 3 (prevascular; 81.1%), 7 (subcarinal; 73.0%) and 2 (upper paratracheal; 70.2%). Zone nine (pulmonary ligament) and peri-diaphragmatic zones were rarely affected in either Hodgkin’s lymphoma.
Out of fourteen patients with MRI done after starting chemotherapy sessions; ten patients were diagnosed as Hodgkin lymphoma (71.428%), and four patients were diagnosed as non-Hodgkin lymphoma (28.571%). ADC range in treated Hodgkin lymphoma cases presented with residual lymph node presentation was 1.04 to 3.6 with ADC average 1.573. ADC range in treated non-Hodgkin lymphoma cases presented with lymph node presentation was 0.72 to 2.7 with ADC average 1.094, while ADC mean in one case presented with mass was 1.29.
In this study, there was statistically significant difference of ADC values in cases presented by masses before and after chemotherapy, while there was statistically insignificant difference of ADC values in case presented by lymph nodes before and after chemotherapy. These findings may be attributed to relatively small sample size.
This is agrees with Lin et al. , who stated that functional information provided by diffusion MRI are potentially helpful in assessment of response to treatment. Littooij et al.  stated that ADC measurements could be a valuable for the differentiation between viable and non-viable residual lesions.
De Paepe et al.  stated that DWI may be used as a response marker very early during treatment for lymphoma.
In two cases who had received chemotherapy, there was a residual anterior mediastinal mass lesion that was considered as residual lymphoma; however their ADC values were 2.6 and 2.7, suggesting benign nature rather than lymphoma residual. The possibility of thymic hyperplasia was considered and was proved by histopathology.
In agreement with Zhen et al.  who stated that thymus hyperplasia following chemotherapy can occur in both children and adults, but occurs most often in children, adolescents and young adults. It can occur in various types of tumors including lymphoma.
One case (7%) showed multiple residual lymph nodes; most of them showing facilitated diffusion denoting benign nature while only two showed restricted diffusion with ADC value reflecting malignancy. In agreement with Chowdhury et al.  and Spiekermann et al.  who stated that sarcoid like reactions have been described in association with many different types of malignancy.
In agreement with Sabri et al.  and Ibrahim et al. , who stated that DWI MRI can differentiate benign from malignant mediastinal masses and can differentiate lymphoma from sarcoidosis in the setting of mediastinal and hilar lymphadenopathy.
However as many studies, this study encompasses some limitations. First of them is the susceptibility artifacts despite the usage of phase array coil with cardiac gating and respiratory compensation techniques to improve image quality and speed. However, these artifacts were not severe enough to interfere with the diagnostic information gained by different MR sequences.
The second limitation is the relatively small number of cases, so we recommend further research on a larger population to confirm our results.