A selection of histologically proven cases of MPM from a five-year institutional database was made to illustrate pre and postsurgical imaging findings.
Presurgical imaging - diagnosis and staging of MPM
The most common presenting symptoms in patients with MPM are chest pain and dyspnoea.[1] Additional symptoms may include cough,
malaise and weight loss.[3]
The diagnosis of MPM is typically made with image-guided core or surgical biopsy.
[1] There are three major histologic types of MPM: epithelioid,
sarcomatoid and biphasic.
Epithelioid is the most common type while non-epithelioid tumour histology predicts a worse prognosis.
[7]
The most common imaging features of MPM are pleural effusion,
pleural thickening,
ipsilateral volume loss,
local invasion,
lymphadenopathy and metastatic disease.
Asbestos-related pleural disease may also be present.
The presence of one or more of these radiologic findings should raise suspicion for MPM,
particularly in the appropriate clinical context.
[1]
The diagnosis is often suggested by unilateral pleural effusion together with focal pleural masses (or diffuse pleural thickening) seen on chest radiographs,
but CT is the imaging modality of choice to evaluate MPM.[3] CT allows to assess the extent of the primary tumour (tumour size,
invasion,
and location),
intrathoracic lymphadenopathy and extrathoracic spread.
[1] Common CT findings include: [1,3,8]
- unilateral pleural effusion (figures 1 and 2);
- pleural thickening (including the interlobar fissures) that can vary from focal nodular thickening to complete rind-like encasement of the entire lung.
Nodular and circumferential pleural thickening greater than 1 cm in thickness and mediastinal pleural involvement are highly suggestive of malignant pleural disease (figures 3 and 5);
- volume loss of the affected hemithorax (figure 3) with associated ipsilateral mediastinal shift,
narrowed intercostal spaces,
and elevation of the ipsilateral hemidiaphragm;
- asbestos-related pleural disease (figure 4) may be seen,
represented by calcified pleural plaques (linear calcification on thickened plaques).
These findings should not be mistaken for osteocartilaginous differentiation (rare and identified by large or punctate foci of mineralization within the tumour);
- intrathoracic lymphadenopathy: ≥10 mm in short axis diameter is considered abnormal for paratracheal,
hilar,
paraesophageal and paraaortic nodes,
while even smaller lymph nodes in the internal mammary are suspicious.
However,
CT accuracy in the detection of nodal involvement remains suboptimal because enlarged nodes alone do not prove nodal involvement;
- local invasion/extension is frequent (namely chest wall,
mediastinum,
and diaphragm).
Chest wall involvement may manifest as loss of normal extrapleural fat planes,
invasion of intercostal muscles,
rib displacement,
and possibly destruction of adjacent bones.
Direct mediastinal extension also causes infiltration of fat planes.
Tumours may also invade local vascular structures and organs (including oesophagus or trachea) usually seen as a soft tissue mass surrounding more than 50% of the structure.[2]
Pericardial involvement is suggested by nodular pericardial thickening that may be accompanied by a pericardial effusion.
[2]
Transdiaphragmatic extension of MPM is suggested by a soft-tissue mass that encases the hemidiaphragm.
Conversely,
a clear fat plane between the diaphragm and adjacent abdominal organs and a smooth diaphragmatic contour suggests that the tumour is limited to the thorax.[8]
- pulmonary metastases and rarely extrathoracic spread of MPM (such as direct hepatic invasion,
retroperitoneal extension,
retrocrural adenopathy).
The differential diagnosis for MPM includes pleural metastases,
solitary fibrous tumor of the pleura,
epithelioid hemangioendothelioma and metastatic dissemination of thymoma.[3]
MPM staging is most commonly performed using the TNM (tumour,
node,
metastasis) system proposed by the International Mesothelioma Interest Group (tables 1 and 2).
[9,10]
In the majority of MPM cases,
CT alone is enough for staging purposes.
[1,3] Positron emission tomography with CT (PET/CT) and thoracic magnetic resonance (MR) can be adjunctive examinations to define tumor staging and resectability,
particularly in questionable cases.[3,8] PET/CT can effectively demonstrate intrathoracic and extrathoracic metastatic disease.
MR has a greater sensitivity than CT for detecting invasion of the chest wall,
mediastinum,
and diaphragm and may be helpful to further examine the local extent of tumor,
especially in surgical candidates.
[1,2]
Surgical therapy for MPM – options and controversies
Surgery for MPM incorporates procedures for diagnosis and staging,
debulking operations for palliation and macroscopic complete surgical resection for curative intent.[11]
There are basically two types of surgical approaches in the treatment of MPM: [4-6]
- extrapleural pneumonectomy (EPP) is defined as a complete,
en bloc,
removal of the whole lung,
including the parietal and visceral pleura,
the ipsilateral hemidiaphragm and the pericardium.
- pleurectomy/decortication (P/D) with parietal and visceral pleurectomy to remove as much as possible of the tumour,
but sparing the entire lung.
There is a variety of different procedures,
ranging from partial pleurectomy (PP),
a cytoreductive procedure (with diagnostic or palliative purposes),
to extended P/D for a curative intent,
in which additional resection of the pericardium and/or the diaphragm is performed.
The diaphragmatic and pericardial defects must be repaired,
generally using prosthetic meshes with several types of prosthetic materials,
either artificial or biologic,
absorbable,
or nonabsorbable.[6]
Surgical management remains controversial.[4,5] During the last decade,
in cases of resectable MPM,
the extrapleural pneumonectomy (EPP) was generally performed but,
recently,
the role of EPP is widely discussed,
especially after the publication of the results of the MARS (Mesothelioma and Radical Surgery) trial.
This multicentre randomised controlled trial suggested that EPP (compared with no EPP,
in the context of trimodal therapy) offers no survival benefit and possibly harms patients.[12]
Indeed,
EPP is an extensive surgery and it is associated with a higher mortality and morbidity rate comparing to P/D.[4] This difference in perioperative mortality (with apparently no difference in long-term survival) has led to a recent trend towards preference to P/D.
[11] The type of surgery also depends on clinical factors and on individual surgical judgment and expertise.[4]
Postsurgical imaging
There is a range of expected normal findings after surgery for MPM according to both the technical procedure and timing of imaging studies.
The imaging appearance of the thorax changes incrementally after EPP.
The entire ipsilateral lung is resected along with the visceral and parietal pleural layers and a gradual opacification of the vacant hemithorax is expected.
Immediately after surgery,
the pneumonectomy space contains mostly air and then starts to fill with fluid (figure 6).
After EPP,
the pneumonectomy space fills with fluid faster than following a standard pneumonectomy (several days following surgery rather than several weeks) likely because of the absence of fluid resorption after excision of the pleura.[13,14].
The mediastinum habitually remains in the midline during the first postoperative days,
typically becoming fixed in position within 7–10 days; contralateral shift may occur if fluid accumulation is rapid.[15]
Reconstruction of the ipsilateral hemidiaphragm and pericardium with prosthetic meshes is performed in EPP and also sometimes in PD (figures 7 and 8).
A diaphragmatic prothesis can often be identified and its appearance depends on the material used for reconstruction.[2] The mesh eventually becomes radiopaque but may appear radiolucent in the early postoperative phase and this finding should not be erroneously interpreted as pneumoperitoneum.
On the other hand,
there are several complications after surgery for MPM,
mainly after EPP,
that can result in significant morbimortality (table 3).[11]
Imaging can play a central role in the identification and subsequent management of many surgical-related complications.
Chest radiographs are typically used to follow patients after surgery for MPM.
If any unexpected changes are found,
CT may be helpful in distinguishing between recurrent disease,
an infectious process or post-treatment complications.
[2,13]
Recurrent disease on thoracic CT typically appears as pleural thickening or a soft tissue mass (figure 9) and mediastinal or hilar adenopathy. Following P/D,
PET/CT aids in distinguishing recurrent tumour from granulation tissue as irregular and nodular soft tissue along the resection margins can be seen in both instances.
[13] After EPP,
recurrences may be local,
but are more frequently distant.[15]