ALK-positive histiocytosis involving the cavernous sinus: A deceptive radiologic mimic of meningioma

FDG PET/CT in ALK-positive Histiocytosis of the Nasal Cavity in a Pediatric Patient

Anaplastic lymphoma kinase (ALK)-positive histiocytosis is a rare newly recognized subtype of histiocytic neoplasms. The disease can involve multiple systems or single system. We present FDG PET/CT findings in a pediatric patient with ALK-positive histiocytosis isolated to the left nasal cavity. The nasal cavity tumor invaded the nasal septum, left nasal bone, and left ethmoid sinus and showed intense FDG activity with an SUVmax of 9.9.

Imaging features of ALK-positive histiocytosis with neurological involvement: a case report and literature review

Background

ALK-positive histiocytosis is an exceptionally rare neoplasm of histiocytes that predominantly involves the nervous system and can also affect the skin and other parts of the body. Previous relevant literature has provided limited information regarding the imaging manifestations of this disease with neurological involvement.

Methods

We reported a case of ALK-positive histiocytosis with multisystem involvement. Together with a comprehensive literature review, the imaging characteristics of this disease in the nervous system were summarized.

Results

A 3-year-old girl with abdominal pain and ambulation difficulty checked in at the Department of Pediatric Neurology. The initial diagnosis was "acute cerebellitis with ataxia" based on the elevated protein level in the cerebrospinal fluid (CSF). However, despite 3 months of treatment, her condition deteriorated. MRI showed an oval-shaped, intradural extramedullary nodule at the T6-T7 level. The patient was ultimately diagnosed as ALK-positive histiocytosis, accompanied by cauda equina and skin involvement. The literature review showed a total of 23 patients who had involvement of the nervous system and provided imaging descriptions. Together with our case, the imaging features were summarized as follows: iso-dense or slightly hyperdense on computed tomography (CT), isointense or iso-hypointense on T2-weighted imaging (T2WI), moderate homogeneous enhancement with mildly/markedly punctate enhancement or/and smooth ring enhancement on contrast-enhanced T1-weighted imaging (T1WI), restricted diffusion on diffuse weighted imaging (DWI), and elevated fluorodeoxyglucose (FDG) uptake on positron-emission tomography/computed tomography (PET/CT).

Conclusion

The multimodal imaging findings of ALK-positive histiocytosis exhibit distinct characteristics, familiarity with which will enhance radiologists' expertise and facilitate accurate diagnosis of this disease.

Neuroimaging manifestations of paediatric histiocytoses

Histiocytoses are rare multi-system disorders marked by abnormal histiocyte cell proliferation, affecting children with diverse clinical presentations. Classified into five groups in 2016, including Langerhans-related (L), cutaneous (C), malignant (M), Rosai-Dorfman disease (R) and haemophagocytic lymphohistiocytosis (H), newer entities such as ALK-positive histiocytosis have also emerged, heralding the era of molecular (sub)classification. Common entities include Langerhans cell histiocytosis (LCH), Erdheim-Chester disease (ECD), Rosai-Dorfman disease (RDD) and haemophagocytic lymphohistiocytosis (HLH). This pictorial essay aids radiologists in recognising and differentiating paediatric histiocytoses based on unique neuroimaging features.