Teaching Case

A 62-year-old non-smoker woman presented with cough and progressive dyspnoea. The patient was referred for asthenia, anorexia, and weight loss for the past 3 months. She denied fever for the same period.

At the time of presentation, the patient had a type 1 respiratory failure (hypoxemia and hypocapnia) with negative inflammatory markers.

On chest radiography (Fig 1), uncountable patchy opacities, some of which confluent, were diffusely seen distributed on both lungs, without a preferential location. Pleural effusion or hilar enlargement were not documented.

Subsequently, the patient performed a Computed Tomography (CT) Angiography, to exclude pulmonary embolism due to a very high level of D-dimers. There weren’t any filling defects seen in the branches of the pulmonary arterial system. CT (Fig 2) showed multiple solid nodules, randomly distributed throughout both lungs. Some of these nodules were centrally cavitated. Consolidation areas with air bronchograms were seen on both basal lung segments. No pleural effusion or hilar adenopathies were shown.

During the inpatient treatment, a bronchofibroscopy was performed with no definite result. The diagnosis was obtained by CT-guided transthoracic core needle lung biopsy (Fig 3), showing showed goblet cells with abundant cytoplasmic mucin and small basally oriented nuclei with minimal atypia and predominantly lepidic growth.

Background

Invasive mucinous adenocarcinoma, once called mucinous bronchioloalveolar carcinoma, is a rare variant form of lung invasive adenocarcinoma. This type of adenocarcinoma is distinguished from non-mucinous adenocarcinoma and it has been re-classified in the international association for the Lung Cancer / American Thoracic Society / European Respiratory Society [1] because of its clinical, radiological pathological, and genetic idiosyncrasies.

Clinical perspective

Invasive mucinous adenocarcinoma has a high frequency in non-smoker women [2], with younger age at presentation, compared to other lung cancer types [1]. Patients may show no symptoms or display non-specific symptoms, such as dyspnoea, cough, sputum, or haemoptysis.

Imaging Perspective

Imaging features may be variable. Both multifocal and solitary forms of invasive mucinous adenocarcinomas tend to be found at the lower lobes [3].

Typical computed tomography findings are characterized by lobar or segmental consolidations, ground-glass opacities, and nodules. A focal nodule or mass is less frequent.  Thin-wall cysts can be present although being rare [4]. 

Positron Emission Tomography-CT (PET-CT) may show only mild fluorodeoxyglucose (FDG) uptake because of the abundant mucin component [5]. 

Invasive mucinous adenocarcinoma tends to be multifocal and multilobar. [3, 6] Histology consists of tall columnar cells with abundant cytoplasm that contains apical mucin and small basal nuclei.

Although being predominantly invasive, these lesions also usually have a lepidic pattern. They are often peripheral with desmoplastic reaction and mucin production. They are usually multifocal in up to 25% of cases [7].

Outcome

Invasive mucinous adenocarcinoma is an aggressive lung tumour, with a much poorer prognosis compared to other lung adenocarcinomas [1]. Early diagnosis is challenging but essential to treat this malignancy.

Take home message / Teaching Point

• Radiologists should be aware of the spectrum of imaging findings in lung adenocarcinoma lesions.
• Invasive mucinous adenocarcinoma is a rare adenocarcinoma of the lung, but important to consider as a differential diagnosis of lower lobe consolidations, cavitations, and small multifocal metastasis.
• Lung biopsy is fundamental to obtain a final diagnosis