{'fraction_non_alphanumeric': 0.02172437202987101, 'fraction_numerical': 0.008146639511201629, 'mean_word_length': 5.436681222707423, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
LEPTOMENINGEAL MELANOSIS – A TRUE PEDIATRIC PATHOLOGY/CYTOLOGY CHALLENGE

Leptomeningeal melanosis is a rare entity and often missed on cerebrospinal fluid (CSF) examination. We present two recent cases where the CSF examination was initially reported as negative. A 15year‐old presented with headaches, back pain and an initial diagnosis of an arteriovenous fistula; progressively worsened clinically with concern for increased intracranial pressure. A shunt was placed. The second patient was a 3 year‐old with vomiting and lethargy. Cranial imaging studies showed mildly dilated ventricles with no discrete lesion. CSF analysis in both cases showed blood, hemosiderin‐laden macrophages and rare atypical cells in clusters. These cells were bland with benign appearing nucleus, abundant cytoplasm and cytoplasmic blebs. Rare cells show prominent nucleoli and intranuclear inclusions. They were positive for HMB45 and S‐100. Ultrastructural studies showed melanosomes, consistent with a diagnosis of leptomeningeal melanosis. Review of initial imaging showed diffuse thickening and enhancement of the leptomeninges. In the past 18 years, 7 cases were seen at our institution (5 previously reported in Cancer). In most of these patients the diagnosis was missed at initial CSF evaluation as the neoplastic cells were often overlooked as histiocytes. Therefore, it is important to be aware of this entity as the clinical course is aggressive and uniformly fatal in children.