Thoracic involvement in generalised lymphatic anomaly (or lymphangiomatosis)

Pathology

GLA is characterised by the presence of lymphangiomas in different organs. As solitary lymphangiomas, they are likely due to a lymphatic developmental abnormality [9–11]; the influence of hormonal factors or a subtler defect requiring a longer growth period have been proposed to explain the presentation of GLA at an older age [1].

The histopathology of GLA resembles that of lymphangiomas, showing an increased number of dilated anastomosing lymphatic channels, lined by endothelial cells [4, 5]. The anastomosing spaces can be filled with chyle or eosinophilic material [1, 16, 17]. These lesions always have a benign appearance and are composed of mature cells, although they may infiltrate tissues [5] (figure 1a). Bone involvement is usually characterised by lytic lesions; bone biopsies of these lesions will show that they are lymphangiomas containing lymphatic fluid [1].

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FIGURE 1

a) Biopsy of the left parietal pleura in a case of generalised lymphatic anomaly showing complex proliferation of vascular spaces infiltrating fibroadipose tissue. Haematoxylin and eosin staining. b) In different areas, the walls of the lymphatic channels are formed by smooth muscle cells expressing desmin but not oestrogen and progesterone receptors. No reaction with the monoclonal antibody HMB-45 was found. c, d) The lymphatic endothelium is characterised by a diffuse and strong expression of D2-40, shown here at two different scales. Images courtesy of Barberis Massimo (Istituto Europeo di Oncologia, Milan, Italy).

Diffuse pulmonary lymphangiomatosis (DPL) usually involves both lungs and has no extrathoracic lymphatic involvement, although one case of a patient with single-lung involvement and histopathological findings compatible with DPL has recently been described [1, 18]. Histologically, DPL is characterised by a proliferation of complex anastomosing lymphatic channels with a significant expansion of pre-existing lymphatic routes within the lungs and mediastinum [3]. Compared with primary pulmonary lymphangiectasis, a substantial amount of collagen and spindle-shaped cells surround the endothelial-lined lymphatic channels. Haemosiderin-laden macrophages may be present in the adjacent lung parenchyma, which, in contrast to lymphangioleiomyomatosis (LAM), is always preserved with no evidence of cystic changes [19, 20].

The endothelial cells lining lymphatic channels in GLA react with anti-CD31 antibodies, which recognise platelet–endothelial cell adhesion molecule 1 [15, 17]. Lymphatic endothelial cells also react with the antibody D2-40, which recognises podoplanin, a more specific transmembrane protein regulated by the lymphatic transcription factor PROX1 [15, 21, 22] (figure 1c and d). Spindle cells variably express smooth muscle cell proteins, reflected in their positivity to antibodies that bind antigens commonly found in these cells such as actin, vimentin and desmin. However, in contrast to cells involved in LAM, they lack oestrogen receptor and glycoprotein gp100, which reacts with the monoclonal antibody HMB-45 [3, 23] (figure 1b). Usually, progesterone receptor is not found [24].

Clinical manifestations

Although GLA mainly presents in childhood [1, 12, 25], it has been diagnosed in patients in all age groups, up to even 80 years old [12, 13]. Males and females are affected similarly [1, 12, 13].

Thoracic GLA may occur as an isolated entity but it is more frequently a multisystem disorder [26] with bone lesions, splenic lesions, cervical involvement and skin involvement [27]. The bones are involved in >75% of patients with GLA [1]. Bone involvement, which can occur with or without lung involvement, can present with pain and pathological fractures but, in contrast to GSD, is characterised by lytic areas confined to the medullary cavity without extensive cortical destruction [28]. The prognosis for GLA is variable and depends on the extent of the disease and involvement of critical organs. Patients with liver, spleen and thoracic duct involvement usually have a poor prognosis because the lesions tend to be diffuse and are not accessible for surgical excision [11].

Within the thorax, single or multiple lymphangiomas may be discovered in the mediastinum, pleura, heart, lung and chest wall [1] (figure 2). Proliferation of lymphangiomas only within the lung leads to the rare syndrome of DPL [3].

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FIGURE 2

Thoracoscopic images showing two different views of a mass enveloping the thoracic aorta and lesions connected to the thoracic wall, diagnosed as lymphangiomas at histological examination of the biopsy. Images courtesy of Spaggiari Lorenzo and Gasparri Roberto (Istituto Europeo di Oncologia, Milan, Italy).

DPL, especially in paediatric populations, can often have a progressive evolution to respiratory insufficiency and death [15]. In a review of 53 cases of thoracic involvement in GLA from the literature, Alvarez et al. [27] reported that patients up to 16 years of age had a worse prognosis than older ones (39% versus 0% mortality). The clinical presentation in adults depends on the location and extent to which lymphangiomas have spread [15]. Nonspecific symptoms sometimes occur, such as mild wheezing, nonproductive cough, chest pain, chest tightness, shortness of breath, dyspnoea and the disease is often misdiagnosed as asthma or other respiratory illnesses [24]. Sometimes massive pleural effusion and progressive pulmonary infiltration cause respiratory failure [15]. Pleural effusions are often chylous, due to spontaneous rupture of diseased lymph vessels within the lymphangiomas [26], and patients may have associated chyloptysis [29], haemoptysis [6, 30, 31] or chylopericardium [32]. In some case reports, chylous ascites, protein wasting enteropathy, peripheral lymphoedema, hemihyperplasia and lymphopenia have been also described [1] (figure 3). DPL patients may rarely present with fever caused by a concurrent pulmonary infection [18]. Although the mechanism is not yet well understood [33], disseminated intravascular coagulation (DIC) has sometimes been associated with thoracic lymphangiomatosis [23, 27, 33]. It has been suggested that the coagulopathy may cause local fibrinolysin production by lymphangiomas [34] or that a mechanism similar to that of the coagulation abnormalities associated with venous malformations may be involved [27]. It has been reported that the presence of a coagulopathy is not always associated with a poor prognosis [27]. Recently, DIC has been associated with a new distinct lymphatic anomaly known as kaposiform lymphangiomatosis (KLA). KLA is characterised histologically by spindled lymphatic endothelial cells, and clinically by a worse progression with haemorrhagic effusions and haematological anomalies, particularly moderate thrombocytopenia (50–100 000 platelets per μL) [35–37].

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FIGURE 3

a) Massive chylous pleural effusion with contralateral shift of mediastinum and b) chylous ascites in a young patient with histological diagnosis of generalised lymphatic anomaly.

Diagnosis

Often, a definitive diagnosis of GLA is delayed because of the rarity of the disease and its different course in each patient [38]. Concomitant lytic bone lesions and chylothorax/pleural effusion could be indicative of this disease given that lymphangiomas are most commonly present in lung and bone [1]. In particular, because of the often slower course of GLA, making a diagnosis of DPL in adults is difficult [39].

Chest radiography can detect diffuse interstitial infiltrates and pleural effusions, which are nonspecific signs of DPL [15]. On high-resolution chest computed tomography, some common characteristics are suggestive, but are not pathognomonic, of DPL [15]. One such instance is the presence of bilateral smooth thickening of the interlobular septa and bronchovascular bundles, which indicates growth of anastomosing lymphatic vessels in the interlobular and central peribronchovascular interstitium [7, 40–42]. Frequent patchy ground-glass opacities may be found, which, according to some authors [3, 41], represent a recent haemorrhage and haemosiderin-laden macrophages in the air spaces [43]. Proliferation of lymphatic channels causes accumulation of lymphatic fluid in the mediastinal and hilar soft tissue; mediastinal soft tissue infiltration, however, seems to have no mass effect on mediastinal vessels [44]. Finally, bilateral pleural effusions are typical [17] and are sometimes chylous but often serosanguineous [41, 44]. These features are generally present in both lungs but Zhang et al. [18] reported a 24-year-old patient with DPL initially located in one lung.

DPL lesions are different from the pulmonary lesions of systemic disease. In systemic disease, Laverdiere et al. [45] described cystic lesions with linear opacities in both lungs. In another case of diffuse systemic lymphangiomatosis, massive chylothorax was reported without pulmonary parenchymal infiltrations [46].

A restrictive pattern is typical on pulmonary function testing although often, a mixed pattern is present [15].

Bronchoscopy is nonspecific, sometimes revealing airway mucosal erythema and oedema, as well as bronchial narrowing. In advanced cases, thin-walled vesicles containing chylous fluid have been found [17]. Although one case of DPL was diagnosed with transbronchial biopsy [7, 43], in most cases reported in the literature, the diagnosis was made with open-lung biopsy [3, 41, 47]. In cases of bone involvement, a bone biopsy may be considered. However, some authors advise not to perform rib biopsy because of the higher risk of developing refractory pleural effusions after this procedure [37].

To obviate the need for a surgical biopsy, other authors have relied on lymphography for a definitive diagnosis of GLA [48, 49]. Lymphangiography has helped differentiate lymphangiomas from haemangiomas and malignant tumours, and accurately evaluate the extension of lesions [1, 50]. However, it is a technique that may cause pulmonary complications since it requires the cannulation of a lymphatic vessel into which an oil-based dye is directly injected [51]. An alternative technique that has been used in children with chylous effusion is the intranodal lymphangiography, a less invasive method of lymphangiography with sonographically guided injection of contrast into a lymph node [52]. Some authors have described the efficacy of lymphoscintigraphy in evaluating disorders of the lymphatic system [53, 54]. Compared to lymphangiography, lymphoscintigraphy is minimally invasive and is not known to have any side-effects but lymphangiography provides more detailed images [33]. Magnetic resonance imaging (MRI) is also an accurate and safe modality to study lymphatic circulation and investigate the pathological lymphatic system of patients with minimal invasiveness and absence of radiation exposure [55]. In particular, lymphatic vessels can be clearly marked on heavily T2-weighted images because of the very slow lymphatic flow within lymphangiomatous malformations [55–57].

In the future, near-infrared fluorescence lymphatic imaging, nanotechnology-based MRI agents, and gene reporter technologies may represent new tools for studying the structure and function of the lymphatic system [58].

Differential diagnosis

Based on clinical and pathological features, GLA should be differentiated from other thoracic lymphatic disorders, some of which are similarly due to congenital errors of lymphatic development, including solitary lymphangiomas, lymphangiectasis and lymphatic dysplasia syndrome [1].

As in GLA, histologically, lymphangiomas are characterised by an increased number of dilated lymphatic channels, lined by endothelial cells. They usually present in early childhood; however, thoracic lymphangiomas may become clinically evident in adulthood or present as accidental findings because of their slow growth. Most thoracic lymphangiomas are found in the mediastinum, while intrapulmonary lesions are extremely rare [1]. Clinical manifestations generally become apparent due to compression of vital structures and/or are related to a secondary infection [59–61].

Primary pulmonary lymphangiectasis usually presents in early life with severe manifestations such as pulmonary hypoplasia and respiratory failure, and is often fatal [62–64]. Radiation therapy, surgery, infection, trauma or tumours impairing effective lymphatic drainage can cause secondary lymphangiectasis leading to respiratory distress at any age. Congenital heart disease in children and severe mitral valve disease in adults can also be associated with lymphangiectasis [65, 66]. Lymphangiectasis is characterised by a dilatation of lymphatic spaces, which in some cases can be cystic, with no evidence of proliferation. A small amount of smooth muscle cells and collagen may be found in the walls of vessels, especially in the secondary form of the disease [3]. The interlobular septa are widened and prominent, and the visceral pleura shows a network of dilated lymphatics.

The “lymphatic dysplasia syndrome” comprises lymphoedema, and effusions of the pericardium, pleura and peritoneum when there is no identifiable cause, and in the absence of lymphangiomas, lymphangiectasis or GLA [30, 67]. The syndrome includes primary lymphoedema, congenital chylothorax, idiopathic chylous effusions and the yellow nail syndrome (i.e. a triad of idiopathic pleural effusions, lymphoedema and dystrophic nails) [30, 67].

LAM is a rare disease of premenopausal women characterised by proliferation of abnormal smooth muscle-like cells (LAM cells) leading to cystic destruction of the lung parenchyma, lymphatic abnormalities and abdominal tumours. Cystic structures in the axial lymphatics (i.e. lymphangioleiomyomas) and chylous pleural effusions are common clinical manifestations of the disease. LAM cells usually express oestrogen receptor and glycoprotein gp100 [68].

Therapy

Treatment is mostly palliative and aimed at slowing the progression of the disease or relieving symptoms related to compression of adjacent structures and chylous fluid accumulation [24]. Different therapies have been tried in patients with GLA but there are no standardised treatment protocols or guidelines for these patients. Due to the rarity of the disease, various treatments have been reported in the literature as part of single case reports or small series of patients.

Dietary treatments, such as total parenteral nutrition, medium-chain triglycerides and high-protein diets, have generally proven to be ineffective [45, 69].

For small or localised lymphangiomas, a surgical approach for thoracoscopy or thoracotomy may be considered, especially if the lymphangiomas cause symptoms because of their rapid growth [70]. When surgery is the chosen option, it is often challenging to differentiate diseased lymphatic tissue from healthy tissue, and complete resection of the affected tissue may prove to be difficult given the proximity to vital structures and organs. Diseased tissue residues can thus proliferate leading to a return of symptoms [71]. Other surgical procedures have included parietal pleurectomy, pleurodesis and ligation of the thoracic duct to reduce recurrent pleural effusion [71–74]. Sclerotherapy has been tested in patients with few lymphangiomas: local injection of agents as Streptococcus antigen OK-432 results in sclerosis of the dilated lymphatic vessels [75]; however, it is a painful procedure that many patients tend to avoid [24]. Molitch et al. [76] treated five patients with percutaneous doxycycline as the sclerosing agent, an approach that proved to be effective for palliative treatment in patients with unresectable lymphangiomas.

Another treatment option is radiation therapy whereby radiation-induced fibrosis of the lymphatic endothelium causes destruction of the lymph vessels [71]. In patients with extensive disease, radiation therapy has resulted in a regression of lesions for several months, although the risk of radiation pneumonitis must always be considered [69].

Systemic chemotherapy [77] and systemic interferon treatment have been tried for patients with extensive and inoperable lymphangiomas, but with limited success [71]. Interferon, which has mild side-effects, seems to stop or reduce lesion growth, but at this time, no data confirm symptom resolution after discontinuation of therapy [45, 78, 79].

Treatment with propranolol, a nonselective β-blocker, may be effective in diffuse GLA. This drug may reduce the levels of vascular endothelial growth factor (VEGF), which is an angiogenic as well as a lymphangiogenic factor, as shown in several studies [80]. In a case report regarding a 13-year-old patient, propranolol was initiated at a dose of 0.5 mg·kg⁻¹ body weight per day and then gradually increased to 4 mg·kg⁻¹ per day. The therapy induced progressive reduction of pleural effusion [81].

In another case report, a 40-year-old woman with GLA was treated with intravenous bevacizumab (1 mg·kg⁻¹ every 3 weeks), a monoclonal antibody that binds to VEGF-A. In this patient, immunohistochemical staining showed increased VEGF-A expression in affected lymphatic vessels compared to healthy vessels. The tumour size decreased with bevacizumab and was stable 10 months after therapy was discontinued due to development of hypertension [82].

Recently, some case reports showed successful treatment with the mTOR inhibitor sirolimus, which proved to be very effective in reducing the disease, with good tolerability and few side-effects, even in newborns [83–86]. The effect of sirolimus on the disease may be explained by our current understanding of the lymphangiogenesis pathway. Activation of the phosphatidylinositol 3-kinase/Akt/mTOR pathway occurs through signalling induced after ligand binging to VEGF receptor 3 on the surface of the lymphatic endothelium [87, 88].

Finally, one case of successful bilateral lung transplantation for DPL has been reported. This experience demonstrated that lung transplantation can be considered as a potential treatment for GLA with pulmonary involvement but accurate selection of patients according to their thoracic, skeletal and abdominal involvement is paramount [89].

The little knowledge we have about the aetiology and pathogenesis of this uncommon disease explains the difficulties in achieving real therapeutic advances. However, despite the absence of an ideal laboratory model for GLA, several promising in vivo models have recently been developed, as reported by Rockson [90]. These models include acquired lymphatic endothelial hyperplasia (attempting to reproduce the histological characteristics of human lesions in lymphangiomatosis), maldevelopment of dermal lymphatics in Wnt5a-knockout mice (showing the role this gene may have in the regulation of normal lymphangiogenesis), pulmonary lymphangiectasia induced by murine developmental VEGF-C overexpression and spheroid-based engineering of a human lymphatic vasculature in mice (a useful technique for the specific study of lymphatic development) [91–95].

Although several cases of thoracic involvement in GLA have been described clarifying the clinical manifestations and histopathology of the disease, further investigation is needed to better understand the pathogenesis of the disease and explore more effective therapeutic approaches. While mTOR inhibitors may represent a valid therapeutic option, clinical trials should be conducted to study the actual effectiveness of these agents for our management strategies. Finally, the development of new imaging techniques specific for the lymphatic system may be useful to examine the spread of the disease and facilitate follow-up.