Neurosurgical Approaches to Pain Management

Medial Thalamotomy

Stereotactic thalamic neuroablative surgery for pain is relatively safe with respect to deep brainstem structures, and because of the wide involvement of many thalamic nuclei in pain processing, it has been considered a part of the pain surgery armamentarium. The first structure targeted for neuroablation was the ventral caudal (Vc) nucleus, as defined by Hassler. However, it was soon recognized that neuroablation of the Vc nucleus was associated with significant deafferentation pain phenomena. The work of Mark and colleagues led to the belief that targeting the medial thalamic nuclei was more effective in managing pain. Nuclear targets for neuroablative medial thalamotomy are (1) the centralis lateralis, (2) the centrum medianum, and (3) the parafascicularis. Several pain syndromes, including cancer pain, central and peripheral deafferentation pain, spinal cord injury, malignancy, arthritis, and neurogenic pain associated with Parkinson’s disease, have been successfully treated by medial thalamotomy. Frank et al. reported the overall success rate of medial thalamotomy to be 52%, with cancer pain being the main condition treated. Jeanmonod et al. and Young et al. used radiofrequency and gamma knife treatment, respectively, and reported a 60% success rate in achieving pain control. The ideal target lying between the three main medial thalamic nuclei (listed above) has yet to be determined, although the centrum medianum nucleus is the most frequently targeted. Deep brain stimulation (DBS) of the medial nuclei does not usually produce a conscious sensory response, and lesioning does not induce sensory loss. The published literature on medial thalamotomy is inconsistent regarding the target, guidance technique, patient population, and lesioning method used. Therefore the actual success rate of medial thalamotomy is challenging to assess. However, in general, the procedure is considered to be effective in treating nociceptive pain, with recent data pointing to some success in relieving neuropathic pain.

Stereotactic Cingulotomy

Cingulotomy refers to stereotactic lesioning of the anterior cingulate gyrus. Le Beau performed the first open cingulotomy to treat intractable pain in 1954, which is believed to cause relief by altering a patient’s emotional reaction to painful stimuli by interrupting the Papez circuit and increasing tolerance to the subjective and emotional feelings of pain. ^, Cingulotomy is performed with standard stereotactic protocols, usually under general anesthesia. Bilateral lesions are made in the anterior aspect of the cingulate gyrus, and the success of the procedure is directly related to the extent of ablation of the cingulum ( Fig. 32.1 ). A suitable stereotactic cingulotomy candidate is a terminally ill patient with widespread metastatic disease that has extended to the musculoskeletal system, where intrathecal or intraventricular administration of opiates is difficult. Emotional factors associated with pain would favor the selection of a stereotactic cingulotomy procedure. Stereotactic cingulotomy has been used to treat non-malignant pain with a success rate of approximately 25%. Stereotactic cingulotomy involves the ablation of sufficient anterior cingulate gyrus volume, which is usually achieved by producing at least two lesions with a wide surface area and non-insulated tip electrode. The procedure is generally safe, with few minor side effects. Pillay and Hassenbusch reported on a series of 12 patients in whom seven had satisfactory pain relief. Cingulotomy is rarely used today, mainly because of its narrow indication, advances in the medical management of terminal cancer patients, and the widespread use of neuroaugmentive procedures.

Caudalis Dorsal Root Entry Zone (Brainstem Level)

Following the introduction of stereotaxis in the 1960s, the use of open ablative brain and brainstem surgery was almost abandoned. Siqueira first reported the performance of the caudalis dorsal root entry zone (DREZ) procedure in two patients. Gorecki et al. at Duke University ^, later adopted the technique and expanded its indications. In the caudalis DREZ procedure, the caudal portion of the spinal trigeminal nucleus, along with the overlying trigeminal tract, is destroyed. Similar to spinal DREZ surgery, the objective is to destroy the cells of second-order neurons thought to be hyperactive in trigeminal deafferentation pain, thereby achieving pain relief ( Fig. 32.1 ). The main indications for the caudalis DREZ procedure are ophthalmic postherpetic neuralgia and trigeminal anesthesia dolorosa. In cases of neuropathic facial pain in which all other medical and surgical modalities are ineffective, the caudalis DREZ procedure may represent a last resort. The procedure is rarely performed, and potential risks include ipsilateral limb ataxia and weakness.

Anterolateral Cordotomy

Anterolateral cordotomy refers to lesioning, sectioning, or other disruption of the lateral spinothalamic tract (LST), which is located in the anterolateral quadrant of the spinal cord. The procedure was historically performed in the upper thoracic spine via an open posterior approach and, less commonly, high in the cervical spine. The spinal cord anterolateral ascending pain transmission system carries information about pain and temperature from one side of the body. The tract is formed by the central processes of nociceptive neurons in the dorsal horn that cross the spinal cord in the anterior commissure, ascend in the anterolateral column to the brainstem, and relay in the thalamus. Lesions of the anterolateral tract produce a contralateral deficit in pain and temperature sensation in two to five segments below the level of the cordotomy. Fibers in the LST have a somatotopic arrangement, with the sacral segments arranged posterolaterally and the cervical segments anteromedially. The corticospinal (pyramidal) tract lies posterior to the LST with the white matter in between. The ventral spinocerebellar tract overlies the LST, and a lesion that damages the spinocerebellar tract may cause ipsilateral ataxia of the arm. Autonomic pathways for vasomotor and genitourinary control and reticulospinal fibers that subserve ipsilateral automatic respiration are also part of the anterolateral quadrant of the spinal cord. A patient with hemibody somatic cancer pain localized caudal to the cervical and upper thoracic areas represents the best candidate for a cordotomy procedure.

From the beginning of the 20th century until the late 1960s to early 1970s, cordotomy was an open procedure undertaken at the mid to high thoracic levels since these sites largely avoided the complications of upper limb ataxia and sleep apnea. Introduction of the minimally invasive percutaneous approach for cordotomy by Mullan et al. mitigated some of the neurologic risks and made it possible for the procedure to be performed on patients in poor general health. ^, In the mid-1980s and early 1990s, advances in opioid pharmacology, as well as the introduction of reversible and testable neuroaugmentive techniques, reduced the perceived need for spinal destructive procedures for pain control and led to a major reduction in the number of cordotomies performed by neurosurgeons worldwide. These neuroaugmentive procedures are expensive, particularly given the short life expectancy of many of the candidates, and are not uniformly effective.

Kanpolat et al. first introduced the concept of computed tomography (CT)-guided cordotomy, which allowed for a safer, selective, and more effective procedure. In 1995, Fenstermaker and associates performed anterior CT-guided lower cervical cordotomy through the disk space to avoid sleep apnea (a modification of Gildenberg et al.’s anterior low cervical percutaneous cordotomy). CT-guided cordotomy is typically performed as a percutaneous procedure via a lateral approach to the spinal cord at the level of C2. However, the anterior cervical transdiscal approach can also be used; in a clinical study, this approach was used to control cancer pain in six of eight patients with ­pulmonary-pleural malignancy while avoiding sleep apnea.

Currently, the CT-guided cordotomy procedure involves lumbar puncture and injection of a water-soluble dye into the patient’s intrathecal space. After 30 min, a cervical CT scan was performed. These and subsequent scans were used to direct the cordotomy electrode into the anterolateral quadrant of the ipsilateral spinal cord. The electrode is insulated throughout the entire shaft except for the tip (2 mm in length and 0.3 to 0.4 mm in diameter). After measurement of the skin-dura distance and local anesthesia of the lateral cervical region, an electrode was introduced from the lateral side of the neck opposite the C2 foramen into the anterolateral quadrant of the spinal cord. Electrophysiologic testing is essential to ensure complete entry into the spinothalamic tract while avoiding the corticospinal tract. Radiofrequency lesions are performed until adequate hypoesthesia is achieved in the contralateral hemibody, or at least in the region of pain. CT-guided cordotomy has a higher success rate and fewer complications than traditional approaches. Control of cancer pain has been reported in more than 95% of the cases. Procedural complications may include weakness, hypotension, dysesthesia, mirror-image pain, ataxia, incontinence, and sleep apnea. Contemporary CT-guided cordotomy complications tend to be both minor and transient.

An evidence-based review concluded that the case for cordotomy is somewhat unique among all cancer pain procedures in that it has the most supportive evidence. The review used the ­Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) system, and a recommendation for cordotomy was given. The GRADE system produces recommendations that are independent of the level of evidence.

Trigeminal Tractotomy-Nucleotomy (Spinal Level)

Sensory information from the 5th, 7th, 9th, and 10th cranial nerves is carried by the trigeminal tract and branches into the trigeminal tract spinal nucleus. It extends caudally into the spinal cord to C2. The trigeminal tract is considered a target for surgical treatment of facial pain, and the history of procedures with this target is similar to cordotomy in that initial open procedures evolved toward less invasive stereotactic operations. Crue et al. and Hitchcock developed a stereotactic technique to lesion the trigeminal tract and nucleus via radiofrequency, named trigeminal nucleotomy. ^, As with CT-guided cordotomy, CT is used when performing the trigeminal tractotomy-nucleotomy (TR-NC) procedure today. Indications include anesthesia dolorosa, post-herpetic neuralgia, neuropathic facial pain, facial cancer pain, and either glossopharyngeal or geniculate neuralgia. ^, The procedure can be considered, in some ways, a mini-caudalis DREZ procedure. The nucleus caudalis DREZ operation involves the same concept as the TR-NC procedure but includes the destruction of the substantia gelatinosa (Rexed laminae II and III) of the nucleus caudalis. Pain relief from TR-NC is reported to be complete or satisfactory in 80% of cases. Complications include ataxia from injury to the spinocerebellar tract (usually temporary) and contralateral hypoalgesia if the spinothalamic tract is included in the lesion. ^{, , ,}