Teaching Case

A 22-year-old male patient presented with recurrent headaches and soft tissue swelling in the right forehead for three months. The patient started to notice the soft tissue swelling only after the recent headaches. The neurological examination was normal. There is no history of trauma to the head and the headaches were not associated with vomiting.

Multidetector Computed Tomography [MDCT] of the skull; lateral projection scout image showed a well defined oval-shaped lytic lesion involving the right frontal bone (Fig. 1). Non-contrast MDCT head in soft tissue window (Fig. 2)  and bone window (Fig. 3)  x in axial plane showed a well-defined osteolytic lesion in the right frontal bone involving both the inner and outer tables of the skull with bevelled edges and without sclerotic margin. The lesion showed epidural and subcutaneous soft tissue components.

Based on imaging, the diagnosis of Langerhans Cell Histiocytosis of the skull was suspected which was confirmed by histopathology.

Langerhans Cell Histiocytosis [LCH], is a proliferative disorder of Langerhans cells. It is a rare disease characterized by the accumulation of macrophage, dendritic cell, or monocyte-derived cells in various tissues and organs of children and adults with a male to female preponderance ratio of 3:1 [1]. A Few authors implicated an autoimmune complex in pathogenesis and some recent studies, based on molecular analysis, have demonstrated that the Langerhans-cell population within LCH lesions is clonal in origin. These data strongly suggest that somatic genetic changes can contribute to the aetiology and pathogenesis of LCH, as documented in neoplastic disorders[2].

Clinical presentations of LCH vary widely, from an asymptomatic solitary bone lesion to multisystem life-threatening afflictions[3]. In bones, this may cause pain and adjacent soft tissue swelling and might cause headaches, as in our patient's case, but most lesions are usually asymptomatic.

LCH can involve any bone, but there is a predilection for the axial skeleton, with more than 50% of bone lesions[4] occurring in the flat bones (skull, ribs, pelvis). Microscopically they show characteristic Birbeck granules and immunohistochemistry reveals the expression of CD1a, CD207, and HLA-DR antigens.

Plain radiography is the initial modality of choice. The usual appearance is a well-defined round/ oval, central destructive,  lytic lesion involving the diploic space with both inner and outer table involvement. The edges of the lesion are often bevelled.

On CT, LCH appears as a solitary or multiple punched out radiolucent defect without reactive sclerosis and is often associated with epidural soft tissue components [3].

On MRI T1 weighted imaging, a mildly high signal intensity lesion is noted. On T2 weighted imaging, a stippled central low signal with peripheral high signal intensity is seen. Areas of irregular central non-enhancement with peripheral enhancement represents central necrosis.

Treatment includes curettage, intralesional steroid injection, or radiation therapy. Mortality and morbidity are associated with the clinical presentation and age of onset of the disease. The worst prognosis is noted in neonates presenting with the disseminated form. This differentiation is important because the prognosis is more favourable with the focal disease rather than multifocal disseminated disease, which involves organs other than the skeletal system

Take home message: Skull is the most common location for LCH. Familiarity with typical imaging appearances of lytic skull lesions is necessary for appropriate patient management.

Written informed patient consent for publication has been obtained.