Localized intrapulmonary desmoplastic mesothelioma: A case report

Desmoplastic mesothelioma typically represents an extremely rare histological subtype of sarcomatoid malignant mesothelioma that usually presents with a diffuse pattern of growth [1] and is commonly found in the pleura and peritoneum. The case of localized intrapulmonary desmoplastic mesothelioma is especially rare, although few cases of true intraparenchymal mesothelioma arising in lung have been described [2,3]. It is dif icult to diagnose these tumors clinically and radiologically, and they can inally be con irmed through pathological examination with immunohistochemistry. The current study reports a case of primary intrapulmonary desmoplastic mesothelioma characterized by a localized mass and without pleural invasion. In addition, the clinical and pathological features of this unusual tumor are included. Written informed consent was obtained from the patient’s family.


Introduction
Desmoplastic mesothelioma typically represents an extremely rare histological subtype of sarcomatoid malignant mesothelioma that usually presents with a diffuse pattern of growth [1] and is commonly found in the pleura and peritoneum. The case of localized intrapulmonary desmoplastic mesothelioma is especially rare, although few cases of true intraparenchymal mesothelioma arising in lung have been described [2,3]. It is dif icult to diagnose these tumors clinically and radiologically, and they can inally be con irmed through pathological examination with immunohistochemistry. The current study reports a case of primary intrapulmonary desmoplastic mesothelioma characterized by a localized mass and without pleural invasion. In addition, the clinical and pathological features of this unusual tumor are included. Written informed consent was obtained from the patient's family.

Case Report
A 52-year-old female consult to the First Af iliated Hospital of Nanchang University (Jiangxi, China) in December 2016 who presented with cough for one month. This patient has no concomitant symptoms of chest (no expectoration and hemoptysis, no fever, no chest pain). The physical examination showed no abnormality, and routine hematological and biochemical parameters were within normal range. The cough without obvious predisposing causes and the patient had not a clear history of asbestos exposure. Anti-infective therapy (Penicillin, intravenous infusion, 2 million to 10 million UU daily) without improvement after one week.
Chest CT scan showed a mass measuring 4.5 x 3.9 cm in the right lung middle lobe with inhomogeneous enhancement ( Figure 1A-E). Based on these indings, an intrapulmonary tumor such as an in lammatory granuloma or lung cancer was suspected.
Exploratory thoracotomy showed a mass measuring 6 x 5 x 4 cm in the right lung middle lobe, without pleural invasion and palpable mediastinal lymph nodes, which the mass tissue is irm and rubbery macroscopically.
The patient had not received chemotherapy or radiotherapy after surgery. As of the time of writing, 10 months postoperatively, the patient has shown no disease recurrence.
Our study was approved by the Ethics Committee of the First Af iliated Hospital of Nanchang University, and the family members of the patient have provided informed consent for the publication of the case.

Discussion
Desmoplastic mesothelioma is a relatively rare histological subtype of mesothelioma with sarcomatoid histology (1) arising most frequently in the pleura, peritoneum or pericardium and less frequently in organs such as lung, spleen [4], pancreas [5] and liver [6]. In fact, few cases of intrapulmonary malignant mesothelioma have been described [2,3,7,8] presenting with bilateral miliary pulmonary nodules and diffuse bilateral opacities or characterized by diffuse intrapulmonary growth, among which some cases [7,8] were pathologically con irmed as intrapulmonary metastases from a clinically undetectable pleural mesothelioma, while the others [2,3] were diagnosed as diffuse intrapulmonary malignant mesothelioma. However, we described an unusual presentation of intrapulmonary mesothelioma characterized by a localized mass without pleural lesions. Clinically and radiologically, the current patient was irst diagnosed as pulmonary in lammatory granuloma or lung cancer. The inal diagnosis of intrapulmonary DMM was con irmed through pathological examination with immunohistochemistry. To the best of our knowledge, there is no previous report of an intrapulmonary desmoplastic mesothelioma presenting as a localized mass without pleural invasion in literature. And it is dif icult to make a de initive pre-operative diagnosis in such case.
Sonja Klebe, et al. [9] reviewed 326 sarcomatoid malignant mesotheliomas with 70 cases (21%) classi ied as DMM and without a case arising in lung and found it occurred more commonly in men. In addition, although mesothelioma is clearly associated with asbestos exposure, the association between DMM and asbestos exposure is controversial [10]. However, the current female patient had not been exposed to asbestos. Patient with DMM typically present with pleural effusion and pleural thickening [11] and are more frequently associated with metastases compared with other series of mesothelioma [12]. However, the current case was presented with a localized mass in the lung parenchyma without distant metastases and marked pleural invasion.
Histologically, DMM is characterized by at least 50% of the tumor consisting of dense, hypocellular collagenous tissue, with paucicellular atypical mesothelial proliferation [11]. It is essential to differentiate intrapulmonary DMM from other pulmonary tumors, such as sarcomatoid carcinoma, because of important differences in treatment and prognosis. Pathological diagnosis is the most reliable diagnostic method. And immunohistochemical staining can aid in making the diagnosis by providing additional characteristic histological information, in that DMM is positive for calretinin and D2-40, but negative for Carcino-embryonic antigen and other carcinoma related markers [13]. Furthermore, pulmonary sarcomatoid carcinoma usually presents as a peripheral mass, especially located at the apex of the lung. histologically adding necrosis, cystoid and mucoid degeneration diffuse distribution, so that enhancement of SFT in arterial phase is not obvious but obvious in the venous phase, which is the characteristic of progressive enhancement. (2) In lammatory myo ibroblastoma of lung: This tumor density was not uniform, so its liquefaction, necrosis, obviously enhancement are common imaging indings.
Currently, DMM without de initive treatment is generally managed according to mesothelioma guidelines. And National Comprehensive Cancer Network guidelines recommend that patient with malignant mesothelioma should receive chemotherapy [14]. In addition, sarcomatoid mesotheliomas are associated with an especially poor prognosis [9], with the median survival time of 3.8 months for DMM patients [11]. However, the current patient was treated without chemotherapy and underwent surgery, and 10 months postoperatively, the patient has shown no local recurrence.
In conclusion, the probability of intrapulmonary malignant mesothelioma should not be ruled out, even in an old female patient presented with pulmonary localized mass without marked pleural lesions.