Abstract
Mesothelioma is an uncommon malignant neoplasm and a localised form of the pleura is especially very rare. Diagnosis of localised malignant pleural mesothelioma (LMPM) is very challenging. Histopathological verification is the gold standard, and studies such as CT, positron emission tomography (PET) and thoracoscopy are very valuable tools in assisting diagnosis. We report a case of histopathologically proven LMPM, which was discovered as a well circumscribed solitary subpleural nodule on PET-CT after presentation with cranial metastasis. This case shows that LMPM can present with uncommon radiological and clinical appearances, and imaging tools such as PET-CT have a very important role in diagnosis.
Background
Malignant mesothelioma (MM) is a rare neoplasm, yet it is the most common primary malignancy of the pleura. It typically presents with pleural effusion or pleural thickening and masses.1 Most of the mesotheliomas present as a diffuse form, but localised forms are also described. Diffuse form is usually associated with asbestos exposure. Localised malignant pleural mesothelioma (LMPM) is a rare tumour,2–4 which usually appears as solitary circumscribed nodule or mass attached, either in a sessile manner or pedunculated manner to the surface of the pleura.5 LMPM should be distinguished from diffuse malignant pleural mesotheliomas, because a good prognosis may be obtained by surgical resection.2 6 Diagnostic imaging involves: standard X-rays, CT, MRI and positron emission tomography (PET). Combination of chest CT and PET shows a high specificity. The best methods for diagnosis are videothoracoscopy and histopathological verification. We present a case of a male patient with a well circumscribed solitary subpleural nodule discovered on PET-CT scan after presentation with cranial metastasis, who underwent video-assisted thoracic surgery (VATS), which was histopathologically proven to be a LMPM.
Case presentation
Three months ago, a 44-year-old male patient was examined because of diplopia and a small parietooccipital cerebral mass detected on MRI at another medical centre. There, he was operated and histopathological examination result was concordant with metastasis. The patient was referred to our clinic for the search of primary malignancy.
Investigations
Initially PET-CT scan, gastroscopy and colonoscopy were performed to rule out lung and gastrointestinal system neoplasms. Gastroscopy and colonoscopy findings were normal. However, PET-CT examination revealed a hypermetabolic subpleural nodule in the left upper lobe lingular segment (figure 1A). Thoracic CT examination showed that the size of the nodule was 15×8 mm and it was oval shaped with smooth contours (figure 1B,C). In addition, emphysematous changes characterised with bullae in the thorax parenchyma more prominent on the upper lobes were noted. The nodule was protruding into a large bulla. There was no pleural thickening or calcification on imaging. The patient had 30 pack-year smoking history. The patient was an accountant and there was no history of asbestos exposure.
Figure 1.
Axial PET-CT image (A) revealing a hypermetabolic subpleural nodule in the left upper lobe lingular segment. The nodule is seen in the mediastinal (B) and parenchymal (C) windows of the thorax CT examination. Note the large bulla adjacent to the nodule in the parenchymal window. PET-CT, positron emission tomography CT.
Differential diagnosis
The lesion appeared highly suspicious and was presumed to be the primary malignancy focus. Differential diagnosis included adenocarcinoma, mesothelioma and benign sequel pleural focal thickening.
Treatment
VATS left upper lobectomy was performed because there was very thin parenchyma remaining due to the bulla. Frozen section procedure was carried out during the surgery and tumour within the bulla was detected as a papillary structure. Lymphadenectomy was also performed. No parietal pleural nodule or thickening was seen during VATS.
Outcome and follow-up
On histopathological examination, the lesion was diagnosed as LMPM and it had the same immunophenotype with the cranial resection material. No subtype was reported. GATA 3, CK 7 and Kalretinin were positive in the immunohistochemical study confirming the diagnosis. The immunohistochemical expression of thyroid transcription factor-1 was also evaluated and it was negative. Lymphadenectomy dissection results were consistent with reactive lymph nodes with anthracosis. The patient underwent chemotherapy and radiotherapy after the surgery. Three months after the operation diffuse metastases were detected in the brain, liver and bones. Biopsy of the lesions from the liver was consistent with MM metastates. Bilateral pleural effusion and ascites occurred. Radiotherapy was performed for the metastatic brain lesions. The patient died a few months later.
Discussion
MM is a very aggressive and treatment-resistant tumour making early diagnosis very important.7 MM usually presents with pleural thickening, calcification and effusion and it is usually associated with long-term asbestos exposure. MM has two forms; diffused and localised. LMPMs are very rare and could present with diffuse parenchymal infiltration without clinically or radiologically detectable pleural lesions.8 Localised forms are difficult to diagnose.9 The patients can be asymptomatic or can present with metastasis. In our case, the patient had a solitary subpleural nodule and did not have any pleural thickening or calcification on PET-CT scan. He presented with cranial metastasis, which is identified in about 3% of cases in recent postmortem studies.10 He also had no history of asbestos exposure. CT scan is the first-line diagnostic tool,11 but PET-CT scan is the gold standard modality for the evaluation of metastatic disease. In our case PET-CT scan was used as the first step to search for the primary tumour. Since early diagnosis is essential, our case shows the importance of recognising that LMPM can present with uncommon radiological and clinical appearance such as a solitary subpleural nodule or with its metastasis. Imaging tools, especially PET-CT have a very significant role in the establishment of this rare diagnosis.
Learning points.
It should be kept in mind that localised malignant pleural mesothelioma can present with uncommon radiological and clinical appearance such as a solitary subpleural nodule or with its metastasis.
Imaging tools, especially positron emission tomography CT have a very significant role in the diagnosis of localised malignant pleural mesothelioma.
Early diagnosis is essential for the treatment of localised malignant pleural mesothelioma.
Footnotes
Contributors: GE, AE and SU made substantial contributions to the conception or design of the work, or the acquisition, analysis or interpretation of data. SU and GE contributed by drafting the work or revising it critically for important intellectual content. GE, AE and SU contributed by approving the final version of the manuscript published.
Competing interests: None declared.
Patient consent: Obtained.
Provenance and peer review: Not commissioned; externally peer reviewed.
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