With the increasing understanding of pain pathophysiology and intrathecal analgesia, implanted IDDS has been widely recognized worldwide for the treatment of various types of chronic intractable pain. IDDS can directly inject drugs into the cerebrospinal fluid, which has the advantages of higher selectivity, significantly lesser doses of drugs and fewer adverse effects (AEs) . However, in order to take advantage of this, proper patient selection and careful application of the therapy needs to be exercised.
This patient had severe unrelenting PHN in the cranial nerve V (trigeminal nerve) distribution, which greatly impacted his quality of life. Despite receiving aggressive multimodal therapies including large doses of oral analgesics and SGB nerve blocks, with no relief of his pain, and subsequently the patient elected to pursue an implantable IDDS with the catheter tip placed at the interpeduncular cistern. After pump placement and initiation of intrathecal hydromorphone, his pain was significantly improved, demonstrating interpeduncular cistern intrathecal targeted drug delivery may be an effective method of treating a plethora of PHN in the trigeminal nerve area.
This case proves that it is particularly important to place the catheter tip in the corresponding position according to the patient's pain level in order to achieve better analgesic effect. Current concepts of Cerebrospinal Fluid (CSF) flow dynamics emphasize pulsatile flow with oscillatory bidirectional craniocaudad CSF movement[7, 8]. Pulsatile flow patterns of CSF have been shown to imposes significant limitations on intrathecal targeted medications delivery via an IDDS, which involves a continuous low-flow intrathecal infusion through a small catheter, such that drugs was limited to a few centimeters of the catheter tip (2–3 vertebrae)[9, 10].
The trigeminal nerve is a mixed nerve, which contains general somatosensory and special visceral movement of two kinds of fibers. Sensory fibers into the pons continue forward to the sensory nucleus, spinal trigeminal nucleus or midbrain nucleus[11–12]. According to clinical experience, the spinal trigeminal nucleus is second order neuron to transmits the pain signal centrally. In spite of this, the catheter tip is always placed far away from the trigeminal nerve root entry zone (where the target receptors are located) in the traditional way, thus possibly leading to insufficient analgesia. Its effect is attributed to the dense concentration of opioid receptors surrounding the brainstem and the CSF flow dynamics theory, the interpeduncular cistern intrathecal targeted drug delivery method for intractable PHN in the trigeminal nerve area could be more effective compared with the traditional approach.
Based on our previous experience, it is difficult to reach the high cervical region by entering the catheter from the relatively safe L2 level due to the lack of a suitable catheter, let alone the intracranial region. Cisterna magna puncture was considered because of its safety, but was abandoned result of difficulty in fixation.Therefore, we chose to puncture through C3-4 and place the catheter tip slowly upwards. The catheter must be advanced slowly into cervical subarachnoid space under continuous X-ray to avoid damage to the tissues. Angle adjustment is very important in the placement process. If the catheter encountered resistance, it was withdrawn and adjust the angle to attempted again. The catheter tip must be exceptionally slow and careful to pass through the C1 level, after which the catheter was easily advanced to this level in our case.
The difficulties of the case mentioned above highlights the need of advancing in intrathecal catheter design, access techniques, imaging, and greater understanding of pain pathway. Technical innovations include new catheters, its tip is soft and the body is strong for easier placement. Ultrasound-guided puncture appears to be a safety technique for the puncture of catheter, while providing better visualization and no radiation exposure.We anticipate that this will occur in several concurrent phases, which will usher in an era where the intracisternal space is recognized as a highly valued therapeutic target.