 Hi, I'm Dr. Shweta, junior resident at Tata Memorial Centre, Mumbai, and today we'll be doing a case series on a relatively unusual topic. So this is a dissemination of low grade biomass expecting the unexpected. So low grade biomass grade one and two are the most common primary CNS neoplasms in children. These include tumor families, according to the WHO 2021 classification. Pediatric type diffuse low grade biomass, circumscribed astrocyclic biomass which are purely grade one tumors mostly, glionuronal and neuronal tumors. So these low grade biomass are generally benign, but may show slow progression to a higher grade. These have been seen in association with the NF1 syndrome. Sporadically, they can have an alteration in the BRAV gene and the type of variations include BRAV fusion and V600E point mutations. So these have prognostic implications. Tumors with BRAV fusion and NF1 syndrome associated generally have favourable outcomes. V600E point mutation has a higher risk of progression and transformation. Now, leptomeningal dissemination is something that is mostly seen with higher grade tumors and it is quite rare in low grade biomass with an occurrence of less than 5% reported in literature. Here we review four cases of disseminated low grade biomass, all of them being grade one pyrocytic astrocytomas at our institute. So let's move on to case one. So this is a 13 year old male child with multiple episodes of vomiting and headache. So MRI was done which showed a solid cystic lesion in the posterior fossa extending into the left cerebellar hemisphere. The solid component was T2 intermediate and it showed nodular post-contrast enhancement with some blooming on SWI. So when we were screening in the post-contrast sequences, we saw there was enhancement along the fourth ventricle and the medulla, which prompted us to screen the spine further. We found nodular enhancing deposits along the cervical, dorsal and the lumbar cord. So near total resection of the fourth ventricular SOL and the leptomeningal nodule in the fourth ventricle was done and that showed a pyrocytic astrocytoma, WHO grade one, however with the leptomeningal deposit. This tumor was beta fusion positive, which if you recall earlier, I mentioned was prognostically relatively good, which was prognostically relatively good. However, still he had a leptomeningal deposit. Post surgery, residual disease was still present and chemotherapy was given. Post chemotherapy, we can see that the deposits have shrunk in size. So this patient is currently still on follow-up and on chemotherapy. Case number two is a three-year-old child with headache and vomiting. She had a large supracella lobulated mass, which was T2 hyperintense, isointense on T1 and showed homogeneous post-contrast enhancement. She underwent sub-total excision of the supracella tumor and that came as pyrocytic astrocytoma, again grade one with beta fusion positive. She was started on tramatinib, which is a MAP kinase inhibitor, which is a targeted therapy for the beta fusion protein and was kept on follow-up. However, on follow-up, she developed parastitiasis for with screening of the spine was done. Screening spine relief revealed enhancing deposits along the subarachnoid space in the dorsal and in the lumbar regions. When Christian-based chemotherapy regimen was added and this patient is still on follow-up and needs to be reassessed. Case number three is a six-year-old girl child with supracella lobulated mass. So a large solid cystic midline mass with heterogeneous post-contrast enhancement. Biopsy was done, which showed a pyrocytic astrocytoma, which was both 600 point mutation and fusion negative. So that means it was a beta-file type tumor. Chemotherapy was given for a year, size was stable and hence she was kept on observation. However, during the observation period, she developed lower limb pain for which we did a MRI spine. So what we noticed was this thin sheet-like enhancement along the whole of the spinal cord. Paneous spinal irradiation was just done and resolution of enhancement was observed with improvement of symptoms. So here we can see that the enhancement which was observed earlier has resolved and she has had stable disease since then and is currently on observation. Fourth case is a 37-year-old female, an adult patient which is relatively uncommon for a pyrocytic astrocytoma. She presented with complaints of headache. MRI showed a lesion in the third ventricle and she was operated outside. However, it does a sub-total resection. So we can see in the MRI that there was a solid cystic tumor in the supra-cellar region and the third ventricle, which was persistent. And the HPI was, as I mentioned earlier, pyrocytic astrocytoma, which was BRAF negative. She however had recurrent headache after a month for which whole ventricular irradiation was done. Post-radiation MRI brain and screening of spine was done, which showed a nodular enhancing deposit along the cauda equina. So that means she progressed on chemotherapy and currently she is on palliation. So with all these cases we observed that these are all low-grade tumors, but we still see leptomeningal dissemination. So this is something we have to keep in mind. Leptomeningal dissemination is infrequent and can occur at any time during the course of the disease with prognostically worsening outcomes. Diagnosis is difficult unless we have a strong suspicion and we carefully review the imaging. Risk factors for this remain unclear. Factors proposed include empanimal invasion, proximity of the tumor to the ventricles and intraoperative ventricular entry. Dian-cephalic location has been reported in literature to have a predisposition to leptomeningal spread. There is no consensus on the most effective treatment yet, but generally these deposits are managed with chemotherapy. So the learning points in this presentation include dissemination is generally seen with high-grade tumors but can rarely occur even in grade 1 tumors. Suspicion of metastasis and prompt imaging should be done when the patient presents with symptoms like backache, parastitiasis and limb weakness. We require a careful review of the post-contrast flare sequences to rule out leptomeningal dissemination in the brain. Thank you.