Author Reply

Dear Editor,

I would like to thank Priola et al. for their interest and comments on our manuscript. As a reply to their specific considerations we would like to mention a few points.

First, as a response to the sentence “Wolfe et al. (1) recently proved the benefit of thymectomy in patients with nonthymomatous myasthenia gravis, including lymphoid thymic hyperplasia, for improving clinical outcomes and reducing the need for immunosuppressive therapy,” we would like to underline that our manuscript reads “while thymectomy is often performed for thymoma, it is not therapeutic for thymic hyperplasia.” This information was based on Kent et al. (2), which is published before Wolfe’s study. Wolfe et al. (1) was not published at the time that our manuscript was submitted, nor accepted for publication (it was published on August 2016). These two important studies present contradicting results on therapeutic thymectomy. Thus, we believe that both studies should be taken into consideration in further research on this topic.

Second, Priola et al. (3) reported that diffusion-weighted imaging (DWI) is a valuable imaging method for defining the normal thymus, by determining unrestricted diffusion with high apparent diffusion coefficient values. Also, it has been shown that, DWI has an important role in differentiation of lymphoid hyperplasia from rebound hyperplasia (3). Since normal thymus and thymic hyperplasia may show similar attenuation, CT is an insufficient imaging method for differentiating these entities. We could not measure CT perfusion parameters of different types of thymic hyperplasia because of the small sample size. All of our four cases with histologic diagnosis were rebound hyperplasia. In our study, the thymic hyperplasia group comprised three patients receiving corticosteroid therapy, two patients undergoing major surgery, two patients with malignancies, and one patient with sepsis.

Third, thymomas exhibit morphologic heterogeneity, with several WHO subtypes often present in the same tumor. The WHO classification system cannot be used to anticipate clinical outcome (4). According to 2004 WHO classification system, the thymomas have five separate histologic subtypes: A, AB, B1, B2, and B3. In our study, the term “benign” was used for defining thymomas of type A to type B3 subtype. We did not compare CT perfusion parameters between the types of thymoma according to the WHO or Masaoka-Koga classification due to the small sample size (n=7). Our cases comprised two patients with type A, one patient with type AB, two patients with type B1+B2, one patient with type B2, and one patient with type B2+B3 thymoma.

Lastly, Mann-Whitney U test was preferred because of the small sample size. Moreover, the groups were not normally distributed. Interquartile range for all groups are given in the Table.

Table.

Interquartile ranges of perfusion parameters for subtypes of anterior mediastinum lesions

	BF	BV	PS
Thymic hyperplasia	33.67–69.57	5.32–12.57	11.66–27.94
Thymoma	48.47–111.7	8.47–19.41	11.33–27.53
Lymphoma	24.91–56.16	3.08–6.82	3.83–14.41
All malignant tumors	25.75–59.43	4.67–8.77	11.43–16.99

This Table is intended to be an addendum to data presented in Bakan et al. (1). Please refer to the abovementioned article for all perfusion parameters data.

BF, blood flow; BV, blood volume; PS, permeability surface.