Teaching Case

A 50-year-old man was referred for evaluation of dyspnoea of 18 months’ duration. No history of smoking, but employed in a factory environment where dilute hydrochloric acid is used. Previously diagnosed with Obstructive Sleep Apnoea-Hypopnoea Syndrome (OSAHS), treated with Continuous Positive Airway Pressure (CPAP) with a favourable response.

CT scan shows enlargement and sclerosis of the right seventh rib with a dysplastic aspect over its entire length with ossification almost to the sternocostal junction (Figure 1). Posteriorly, the rib shows slight periosteal irregularity and an image of small fragmented sessile exostosis or with adjacent heterotopic ossification (Figure 4).

Around the rib, there is a diffuse fatty infiltration of the thoracic wall, more prominent in the posterior half of the thorax (6th intercostal space) (Figures 3, 5a, 5b), extending medially and touching the pleura. There is also another area of lipoma, better defined anterolaterally, of lenticular morphology, in the fatty plane between the intercostal muscle and the oblique (Figure 6).

Sequences taken after contrast administration show no obvious enhancement of the lipomatous proliferation.

As no enhancing non-fatty tissue was detected, the associated rib anomaly and the absence of related symptoms, a diagnosis of transthoracic lipomatosis associated with congenital rib anomaly was made. A wait-and-see approach was decided with MRI examinations, which confirmed the stability of the lesion.

Lipomatous lesions are a common group of mostly benign growths derived from adipose tissue [1]. They may present as solitary or multiple masses, deep or superficial. They are seldom seen in the thorax, although they can be found in many locations. Deep lipomas tend to be less circumscribed than subcutaneous lipomas, and their contours are usually determined by the spaces they occupy without infiltrating adjacent structures.

Deep thoracic lipomas can be divided into three groups according to their location:

1. Intrathoracic: entirely intrapulmonary, subpleural or endobronchial.
2. Cervicomediastinal: from the mediastinum to the neck.
3. Transmural: they have an intrathoracic and an extrathoracic component connected by a fatty isthmus through the intercostal space or, exceptionally, through a sternal defect [2].

Exceptionally, they are associated with adjacent bone abnormalities (localised gigantism or malformation). Such cases have been reported, most of them more than 20 years ago [3,4].

The pathogenesis of the association between lipoma and congenital bone anomalies is unclear. The most widely accepted theory is that the nerve is initially irritated by an unknown cause, leading to abnormal trophic influences that alter the normal development of the soft tissues and bones corresponding to that dermatomal level, ultimately resulting in lipomatosis and dysostosis.

Clinically, they present as asymptomatic thoracic masses, preferably postero-lateral. Due to their slow growth, the symptoms are often due to the mass effect: cough, dyspnoea [5], cardiac dysfunction.

Chest x-ray shows a well-defined mass with intra- and extrathoracic components, with a homogeneous fat density and some metaplastic calcification.

Chest CT confirms the fat attenuation of the mass, together with changes in the morphology and size of the vertebra and the rib of the metameres, with irritative hyperostosis of the adjacent costal cortex.

MRI is useful in describing the extent of the lesion and its relationship to adjacent organs, as well as identifying the fatty nature of the lesion. The administration of intravenous contrast media provides information about the enhancing pattern: the less the lesion enhances, the more likely is to be of benign origin.

In all cases, deep lipomas must be differentiated from liposarcoma or other lipomatous malignancies, and the distinction often requires anatomopathological analysis.

The management strategy is not established. If asymptomatic, radiological follow-up may be sufficient, but some authors recommend biopsy or surgical excision due to the possibility of well-defined liposarcoma [6]. Even if they are histologically benign, surgery is sometimes necessary if there are symptoms due to their size or location.

All patient data have been completely anonymised throughout the entire manuscript and related files.