This is a open-label, single-arm, dose escalation phase I clinical trial. The goal of this clinical trial is to evaluate the safety and preliminary efficacy of Intrathecal injection human umbilical cord-derived mesenchymal stromal cell-derived extracellular vesicle (hUC-MSC-sEV) in syringomyelia.

This is a open-label, single-arm, dose escalation phase I clinical trial. The study will consist of one part: Part 1 will be a dose-escalation study.

A traditional 3+3 dose-escalation design will be implemented in Part 1. Cohort 1 will receive low-dose1×1011particles; Cohort 2 will receive middle-dose2×1011particles; and Cohort 3 will receive high-dose3×1011particles. (Cohort 1 to Cohort 3 will receive a dose of 2 ml per lumbar puncture, administered once a month, for a total of three months.) If no dose-limiting toxicities (DLTs) are observed for 2 weeks after the administration of the first Intrathecal injection, a new cohort will be enrolled at the next planned dose level. If DLTs are observed in one participant in the cohort, an additional three participants will be treated at the same dose level. Dose escalation will be stopped if DLTs are observed in more than 33% of the participants.

Inclusion Criteria:

• Patients whose MR revealed that syrinx have shrunk after surgery for a year but whose clinical spinal cord symptoms have not improved.
• Patients whose MR revealed that syrinx spontaneously resolution under conservative observation, but whose clinical spinal cord symptoms have not improved.
• Age: 18-70 years, inclusion of both genders;

Exclusion Criteria:

• 1. Those with diabetes, heart disease, or impaired liver or kidney function; 2. Those with other diseases such as brainstem tumors and spinal cord tumors; 3. Infected individuals with lumbar puncture sites; 4. Those with previous or detected abnormalities in the heart; 5. Those who have autoimmune diseases and need to be treated with immunosuppressants; 6. Those who are allergic to the research drugs; 7. Have participated in other interventional clinical studies or received other cell therapies (excluding blood transfusion) within the past three months; 8. Those who are unconscious, unable to express subjective discomfort symptoms and unable to cooperate with neurological function tests, those who have been receiving drug treatment for a long time and do not cooperate with the treatment plan; 9. Pregnant women, women who are breastfeeding and those planning to become pregnant; 10. Serological tests (HBsAg, anti-HCV, anti-HIV, TP-Ab) are positive; 11. Other circumstances where the researcher deems the patient unsuitable to participate in this study (including but not limited to not meeting the treatment that benefits the patient the most, poor patient compliance, abnormal laboratory test indicators that cannot be accepted, etc.).

Rejection Criteria:

misdiagnosis; use of any medication that may significantly impact the assessment accuracy of hUC-MSC-sEV engraftment; absence of any evaluation outcome at any time point during the follow-up period

Cessation Criteria:

individual wishes of the subjects; occurrence of any hUC-MSC-sEV-associated serious adverse event (SAE) that may aggravate neurological dysfunction, or require prolongation of existing hospitalization, or need hospital readmission, or impair consciousness, or be life-threatening, or even lead to death in any subject; detection of any major mistake in the present protocol during the implementation of this clinical trial; the national administration agency requires the clinical trial to be halted

The study will not share individual participant data to other researchers.