Langerhans cell histiocytosis (LCH) is an abnormal non-malignant proliferation of monoclonal Langerhans cells within one or multiple organ systems [1, 2]. The presence of Birbeck granule on electron microscopy, and positive CD1a and S-100 immunohistochemical staining confirm the diagnosis . Owing to the relative rarity of the condition, the diagnosis is often delayed or missed. LCH can present at any age (peak incidence at 1-4 years). Patients present with different forms: at one end of the spectrum, single-system disease and at the other end, disseminated LCH involving any organ .
Skin lesions are the most common initial manifestation, presenting as a seborrhoea-like eruption that is often initially misdiagnosed. Bone lesions are also common, which can affect any bone, and frequently occur in the skull. Up to 80% of LCH are an eosinophilic granuloma type, usually producing geographic lytic lesions. Vertebral body involvement causes collapse (vertebral flattening). Plain radiography is generally the first imaging method used to evaluate a bone lesion. CT and MR imaging are useful for providing anatomic detail of the affected bone. CT is better suited for bone detail and MR imaging for bone marrow and soft tissue involvement .
Pulmonary involvement is usually a part of multisystem LCH (42%). In early stages, bilateral diffuse poorly-defined nodules are seen, which undergo cystic degeneration as the disease progresses. Plain films can miss small lung lesions. HRCT plays an important role in the evaluation of pulmonary LCH . A large solid neck mass in lymph nodes with little bone involvement, as occurred in our case, is a rare presentation . Detection of small pulmonary cysts helped in the diagnosis.
Fluorodeoxyglucose PET uptake occurs in solid pulmonary nodules, thick-walled cysts, and extra-pulmonary nodules. Future studies are necessary to investigate the role of PET scan in the diagnostic evaluation of LCH .
In children, the differential diagnosis of a solid neck mass is limited to neuroblastoma (retropharyngeal, with calcifications), rhabdomyosarcoma (often with bone destruction), infectious cervical lymph nodes (solid or necrotic with inflammatory signs), lymphoma (multiple adenopathies), haemangioma (intense enhancement because of high vascular supply), and lymphatic malformation (typically a multilocular fluid-filled mass rather than a solid mass). The differential diagnosis of cystic pulmonary lesions includes sarcoidosis, cavitated tuberculosis, haematogenous infection (necrotic nodules), lymphangiomyomatosis, bronchiectasis, and post-infection pneumatoceles. LCH should be considered in the differential diagnosis of solid masses in children, and prompt physicians to search for visceral organ involvement.