Posterior quadrant disconnection

Posterior quadrant disconnection

Posterior quadrant disconnection (PQD) is surgery for refractory unilateral temporo-parieto-occipital epilepsy to limit the propagation of epileptic discharges. As incomplete disconnection can lead to residual seizures, detailed procedures are presented by Umaba et al. using a cadaveric brain, three-dimensional (3D) reconstruction and simulation models, and intraoperative photographs.

A formalin-fixed adult cadaveric brain was dissected to show each step in PQD. Using 3D preoperative planning software, we reconstructed 3D models from computed tomography and magnetic resonance imaging, and visualized operative views. Intraoperative photographs were taken from the case of a 7-year-old girl with temporo-parieto-occipital epilepsy.

Fronto-temporo-parietal craniotomy is performed. The Sylvian fissure is widely dissected and the insular cortex is exposed. The temporal stem is disconnected along the inferior periinsular sulcus. The disconnection is extended from the limen insulae to the atrium of the lateral ventricle (LV). The fibers between the head of the hippocampus and the amygdala are disconnected. The parietal lobe is disconnected along the postcentral sulcus and the disconnection is connected to the atrium of the LV. At the medial surface of the parietal lobe, the disconnection is continued until reaching the corpus callosum (CC). The splenium of the CC is disconnected via the medial wall of the LV. The fornix is divided in the atrium of the LV. After these steps, disconnection of the unilateral tempo-parieto-occipital lobe is achieved while preserving the arteries and veins.

Inclusion of views from cadaveric brains, 3D reconstruction and simulation models, and intraoperative photographs facilitates a clearer anatomical understanding of PQD 1).

Twenty hemispheres were dissected according to Klingler’s fiber dissection technique illustrating the peri-insular (temporal stem, superior longitudinal fasciculus, corona radiata) and mesial disconnection (mesiotemporal cortex, cingulum, and corpus callosum).

Extensive white matter tract disconnection is obtained after posterior quadrant disconnection. Callosal fibers connecting the anterior most part of the parietal cortex invariably ran through the isthmus of the corpus callosum and need to be disconnected, while frontal lobe connections including the corticospinal tract and the anterior two-thirds of the corpus callosum are spared during the procedure.

The findings suggest the involvement of both the splenium and the isthmus in interhemispheric propagation in posterior cortex epilepsies. Sectioning the total extent of the posterior one-third of the corpus callosum might therefore be necessary to achieve optimal outcomes in posterior quadrant epilepsy surgery 2).

Nooraine et al. analyzed the data of seven (n = 7) consecutive posterior quadrant epilepsy patients who underwent posterior quadrant disconnection with a mean age of 8.5 years over the last three years of which 4 were male and 3 females. All patients underwent extensive pre-surgical evaluation including detailed history, examination, prolonged video EEG recordings, neuropsychological testing, MRI brain, DTI, PET scan (n = 6), fMRI (n = 4), WADA test (n = 1) and invasive recording (n = 1), Of seven patients four had left sided pathology and three had right sided pathology. All patients except one underwent pure disconnection and one underwent partial resection.

Posterior quadrant disconnection is effective surgical procedure for medically refractory epilepsy arising from the posterior quadrant in carefully selected patients without morbidity or functional disability across various age groups especially in children. In our series, all seven patient had good seizure outcome and none had functional disabilities 3).

Ten patients who were surgically treated using the posterior quadrantectomy (PQT) were enrolled in this study. Surgical outcome was analyzed as seizure-free or not at 2 years after surgery. Psychomotor development was evaluated by the scores of mental developmental index (MDI) and psychomotor developmental index (PDI) in the Bayley Scales of Infant Development II preoperatively, and at 6 and 12 months after the PQT. RESULTS:

Eight of 10 patients were seizure-free. Patients without complete elimination of the angiomatous areas had residual seizures. Average MDI and PDI scores before the surgery were 64.8 and 71.6, respectively. Scores of MDI at 6 and 12 months after the PQT in seizure-free patients were 80.5 and 84.5, respectively (p < 0.01). PDI scores at these postoperative intervals were 87.3 and 86.4, respectively (p < 0.05). Patients with residual seizures did not improve in either MDI or PDI. SIGNIFICANCE:

The PQT achieved good seizure control and improved psychomotor development in patients with SWS. The complete deafferentation of angiomatous areas is required for seizure-free results and psychomotor developmental improvement 4).

There were 3 males and 7 females (median age 8.7 years; range 4.2-22.1 years). The affected hemisphere was the left in 3 patients and the right in 7. The patients’ median age at seizure onset was 3.0 years (range 0.2-8.3 years). The median duration of epilepsy before surgery was 5.2 years (range 1.3-17.2 years). The underlying pathology was TPO malformation of cortical development in 5 patients, and venous infarction, posterior hemispheric quadrant atrophy, Sturge-Weber syndrome, cortical involvement of a systemic lupus erythematosus, and gliosis after cerebral tumor treatment in 1 each. In 6 children, a pure TPO disconnection was performed; in 2 patients, the temporal lobe was resected and parietooccipital disconnection was performed. The 2 remaining patients had had previous epilepsy surgery that was extended to a TPO disconnection: disconnection of the occipital lobe (n = 1) and resection of the temporal lobe (n = 1). The authors encountered no complications while performing surgery. No patient needed blood replacement therapy. No patient developed CSF disturbances that warranted treatment. Nine of 10 patients are currently seizure free since surgery (Wieser Class 1a) at a median follow-up time of 2.1 years (range 4 months to 8.1 years). CONCLUSIONS:

Temporoparietooccipital disconnection is a safe and effective motor-sparing epilepsy surgery in selected cases. Technical adjuncts facilitate a better intraoperative visualization and orientation, thereby enabling a less invasive approach than previously suggested 5).

there were 13 patients with a median age of 17 years. All patients had extensive presurgical evaluation that provided concordant evidence localizing the lesion and seizure focus to the posterior quadrant. The objective of the surgery was to eliminate the effect of the epileptogenic tissue and preserve motor and sensory functions. RESULTS:

During the course of this study period of 15 years, the surgical procedure performed evolved toward incorporating more techniques of disconnection and minimizing resection. Three technical variants were thus utilized in this series, namely, (i) anatomical posterior quadrantectomy (APQ), (ii) functional posterior quadrantectomy (FPQ), and (iii) periinsular posterior quadrantectomy (PIPQ). After a median follow-up period of 6 years, 12/13 patients had Engel’s Class I seizure outcome. CONCLUSION:

The results of surgery for posterior quadrantic epilepsy have yielded excellent seizure outcomes in 92% of the patients in the series with no mortality or major morbidity. The incorporation of disconnective techniques in multilobar surgery has maintained the excellent results obtained earlier with resective surgery 6).

An enhanced operative video presents the illustrative case of a total Posterior quadrant disconnection indicated for a 15-year-old boy with Sturge-Weber syndrome suffering from seizure recurrence after a partial PQD. Barrit et al. described the surgical procedure with emphasis on relevant anatomy and multimodal intraoperative guidance in three steps: (i) parieto-occipital disconnection, (ii) posterior callosotomy, and (iii) temporal disconnection/resection. Pearls and pitfalls of surgical management are discussed.

Posterior quadrant disconnection is a less invasive surgical option than typical hemispherectomy for selected indications of posterior multilobar epilepsy 7).


Umaba R, Uda T, Nakajo K, Kawashima T, Tanoue Y, Koh S, Uda H, Kunihiro N, Matsusaka Y, Ohata K. Anatomical understanding of posterior quadrant disconnection from cadaveric brain, 3D reconstruction and simulation model, and intraoperative photographs. World Neurosurg. 2018 Aug 30. pii: S1878-8750(18)31951-X. doi: 10.1016/j.wneu.2018.08.168. [Epub ahead of print] PubMed PMID: 30172981.

Verhaeghe A, Decramer T, Naets W, Van Paesschen W, van Loon J, Theys T. Posterior Quadrant Disconnection: A Fiber Dissection Study. Oper Neurosurg (Hagerstown). 2018 Jan 1;14(1):45-50. doi: 10.1093/ons/opx060. PubMed PMID: 29253283.

Nooraine J, R SK, Iyer RB, Rao RM, Raghavendra S. Posterior quadrant disconnection for refractory epilepsy: A case series. Ann Indian Acad Neurol. 2014 Oct;17(4):392-7. doi: 10.4103/0972-2327.144006. PubMed PMID: 25506159; PubMed Central PMCID: PMC4251011.

Sugano H, Nakanishi H, Nakajima M, Higo T, Iimura Y, Tanaka K, Hosozawa M, Niijima S, Arai H. Posterior quadrant disconnection surgery for Sturge-Weber syndrome. Epilepsia. 2014 May;55(5):683-9. doi: 10.1111/epi.12547. Epub 2014 Feb 22. PubMed PMID: 24621276.

Dorfer C, Czech T, Mühlebner-Fahrngruber A, Mert A, Gröppel G, Novak K, Dressler A, Reiter-Fink E, Traub-Weidinger T, Feucht M. Disconnective surgery in posterior quadrantic epilepsy: experience in a consecutive series of 10 patients. Neurosurg Focus. 2013 Jun;34(6):E10. doi: 10.3171/2013.3.FOCUS1362. PubMed PMID: 23724834.

Daniel RT, Meagher-Villemure K, Farmer JP, Andermann F, Villemure JG. Posterior quadrantic epilepsy surgery: technical variants, surgical anatomy, and case series. Epilepsia. 2007 Aug;48(8):1429-37. Epub 2007 Apr 18. PubMed PMID: 17441997.

Barrit S, Park EH, Madsen JR. Posterior quadrant disconnection for refractory epilepsy: how I do it. Acta Neurochir (Wien). 2022 May 17. doi: 10.1007/s00701-022-05221-x. Epub ahead of print. PMID: 35578117.

Obstructive hydrocephalus from posterior fossa tumor risk factors

Obstructive hydrocephalus from posterior fossa tumor risk factors

Saad et al. from the Emory University Hospital surveyed the CNS (Central Nervous System) Tumor Outcomes Registry at Emory (CTORE) for patients who underwent posterior fossa tumor surgery at 3 tertiary-care centers between 2006 and 2019. Demographic, radiographic, perioperative, and dispositional data were analyzed using univariate and multivariate models.

They included 617 patients undergoing PFT resection for intra-axial (57%) or extra-axial (43%) lesions. Gross total resection was achieved in 62% of resections. Approximately 13% of patients required permanent cerebrospinal fluid shunt. Only 31.5% of patients who required pre- or intraop external ventricular drain (EVD) placement needed permanent cerebrospinal fluid shunt. On logistic regression, Tumor size, transependymal edema, use of perioperative external ventricular drain, postoperative intraventricular hemorrhage (IVH), and surgical complications were predictors of permanent CSF diversion. Preoperative tumor size was the only independent predictor of postoperative shunting in patients with subtotal resection. In patients with intra-axial tumors, transependymal flow (P = .014), postoperative IVH (P = .001), surgical complications (P = .013), and extent of resection (P = .03) predicted need for shunting. In extra-axial tumors, surgical complications were the major predictor (P = .022).

The study demonstrates that the presence of preoperative hydrocephalus in patients with PFT does not necessarily entail the need for permanent CSF diversion. Saad et al. reported the major predictive factors for needing a permanent cerebrospinal fluid shunt for obstructive hydrocephalus 1).

Superior tumor extension (into the aqueduct) and failed total resection of tumor were identified as independent risk factors for postoperative hydrocephalus in patients with fourth ventricle tumor 2).

Cully and colleagues analyzed 117 patients and found the following factors to be associated with a higher incidence of postresection hydrocephalus (PRH): age <3 years, midline tumor location, subtotal resection, prolonged EVD requirement, cadaveric dural grafts, pseudomeningocele formation, and CSF infections 3).

Due-Tonnessen and Hleseth found that patients with medulloblastoma and ependymoma had much higher rates of postoperative shunt placement than astrocytomas 4). Kumar and colleagues in a study of 196 consecutive children found age <3 years, tumor histology of medulloblastoma/ependymoma and partial resections were associated with the increased chances of postresection hydrocephalus 5). A study noted that the only modifiable risk factor for the development of PRH was the presence of intraventricular blood in postoperative imaging 6).

Intraventricular blood can cause hydrocephalus either by the “snow globe effect” 7) or by other factors like impaired absorption of CSF by inflammation and fibrosis of the arachnoid granulations caused by blood degradation products 8).

Gopalakrishnan and colleagues noted the following risk factors for PRH: the need for CSF diversion in the pediatric population—children with symptomatology <3 months duration, severe hydrocephalus at presentation, tumor location in the midline, tumor histology, viz. medulloblastoma and ependymoma, use of intraoperative EVD, longer duration of EVD, postoperative meningitis, and pseudomeningocele 9). Similar findings were also reported by Bognar et al. who showed that the presence of EVD and the duration of EVD were associated with a significant increase in the incidence of postresection CSF diversion. In another recent study, Pitsika et al. 10) showed that patients who underwent EVD had a higher rate of postoperative VPS. They also noted a negative correlation between early EVD clamping and VPS indicating that clamping encourages the re-establishment of normal CSF flow when the obstructive tumor is removed 11). From 12).

Choroid plexus cysts (CPCs) are a type of neuroepithelial cysts, benign lesions located more frequently in the supratentorial compartment. Symptomatic CPCs in the posterior fossa are extremely rare and can be associated with obstructive hydrocephalus

Predictive factors for postoperative hydrocephalus has been identified, including young age (< 3 years), severe symptomatic hydrocephalus at presentation, EVD placement before surgery, FOHR index > 0.46 and Evans index > 0.4, pseudomeningocelecerebrospinal fluid fistula, and infection. The use of a pre-resection cerebrospinal fluid shunt in case of signs and symptoms of hydrocephalus is mandatory, although it resolves in the majority of cases. As reported by several studies included in the present review, we suggest CSF shunt also in case of asymptomatic hydrocephalus, whereas it is not indicated without evidence of ventricular dilatation 13).


Saad H, Bray DP, McMahon JT, Philbrick BD, Dawoud RA, Douglas JM, Adeagbo S, Yarmoska SK, Agam M, Chow J, Pradilla G, Olson JJ, Alawieh A, Hoang K. Permanent cerebrospinal fluid shunt in Adults With Posterior Fossa Tumors: Incidence and Predictors. Neurosurgery. 2021 Nov 18;89(6):987-996. doi: 10.1093/neuros/nyab341. PMID: 34561703; PMCID: PMC8600168.

Chen T, Ren Y, Wang C, Huang B, Lan Z, Liu W, Ju Y, Hui X, Zhang Y. Risk factors for hydrocephalus following fourth ventricle tumor surgery: A retrospective analysis of 121 patients. PLoS One. 2020 Nov 17;15(11):e0241853. doi: 10.1371/journal.pone.0241853. PMID: 33201889; PMCID: PMC7671531.

Cully DJ, Berger MS, Shaw D, Geyer R. An analysis of factors determing the need for ventriculoperitoneal shunts after posterior fossa tumor surgery in children. Neurosurgery 1994;34:402-8.
4) , 8)

Due-Tonnessen B, Helseth E. Management of hydrocephalus in children with posterior fossa tumors: Role of tumor surgery. Pediatr Neurosurg 2007;43:92-6

Kumar V, Phipps K, Harkness W, Hayward RD. Ventriculoperitoneal shunt requirement in children with posterior fossa tumors: An 11-year audit. Br J Neurosurg 1996:10:467-70.

Abraham A, Moorthy RK, Jeyaseelan L, Rajshekhar V. Postoperative intraventricular blood: A new modifiable risk factor for early postoperative symptomatic hydrocephalus in children with posterior fossa tumors. Childs Nerv Syst 2019;35;1137-46.

Tamburrini G, Frassanito P, Bianchi F, Massimi L, Di Rocco C, Caldarelli M. Closure of endoscopic third ventriculostomy after surgery for posterior cranial fossa tumor: The “Snow Globe effect”. Br J Neurosurg 2015;29:386-9.

Gopalakrishnan CV, Dhakoji A, Menon G, Nair S. Factors predicting the need for cerebrospinal fluid diversion following posterior cranial fossa tumor surgery in children. Pediatr Neurosurg 2012;48:93-101

Pitsika M, Fletcher J, Coulter IC, Cowie CJA. A validation study of the modified Canadian preoperative prediction rule for hydrocephalus in children with posterior fossa tumors. J Neurosurg. doi: 10.3171/2021.1.PEDS20887.

Bognar L, Borgulya G, Benke P, Madarassy G. Analysis of CSF shunting procedure requirement in children with posterior fossa tumors. Childs Nerv Syst 2003;19:332-6.

Muthukumar N. Hydrocephalus Associated with Posterior Fossa Tumors: How to Manage Effectively? Neurol India. 2021 Nov-Dec;69(Supplement):S342-S349. doi: 10.4103/0028-3886.332260. PMID: 35102986.

Anania P, Battaglini D, Balestrino A, D’Andrea A, Prior A, Ceraudo M, Rossi DC, Zona G, Fiaschi P. The role of external ventricular drainage for the management of posterior cranial fossa tumours: a systematic review. Neurosurg Rev. 2021 Jun;44(3):1243-1253. doi: 10.1007/s10143-020-01325-z. Epub 2020 Jun 3. PMID: 32494987.

Posterior cervical decompression

Posterior cervical decompression

Not typically used for a herniated cervical disc, more common for cervical spinal stenosisOPLL

● without posterior fusion

● with lateral mass fusion

b) keyhole laminotomy: sometimes permits removal of disc fragment

Usually reserved for the following conditions:

multiple cervical discs or osteophytes (anterior cervical discectomy (ACD) is usually used to treat only 2, or possibly 3, levels without) with myelopathy.

where the anterior pathology is superimposed on cervical stenosis, and the latter is more diffuse and/or more significant

in professional speakers or singers where the 4% risk of permanent voice change due to recurrent laryngeal nerve injury with ACD may be unacceptable.

Laminectomy and facetectomy are commonly used surgical procedures for decompressing cervical spinal stenosis. Resection of the posterior structures causes instability and affects the internal stresses of the cervical spinal components. However, the influence of these surgical procedures on the biomechanical responses of the cervical spine has not been studied.

A nonlinear finite element model of the intact C2-C7 was constructed and validated. Ten surgically altered models were created from the intact model and were tested under physiologic loading. Because of the inclusion of five motion segments, it was possible to determine the intersegmental responses and internal cortical shell and disc stresses in the adjacent altered and unaltered spinal components.

Under combined flexion and extension, intersegmental motions at C4-C5 and C5-C6 increased significantly after C5 laminectomy. Subsequent facetectomy performed at C5 and C6 on the laminectomized model only affected the responses at the C5-C6 segment. Overall, slight intersegmental responses of up to 5% were observed at the adjacent levels of C3-C4 and C6-C7. Laminectomy did not cause any significant increase in the intersegmental motions under lateral bending and axial rotation. Extending the surgical procedures to unilateral and bilateral facetectomy only increased the intersegmental motions slightly. Similar increases in the intervertebral disc and the cortical shell stresses were observed. These findings may partially explain the clinical observations of enhanced osteophytes formation.

This study provides a better understanding of the surgically altered cervical spinal biomechanics and may help formulate treatment strategies such as spinal implants 1).

Its a posterior cervical spine surgery, for cervical spinal stenosis. The spine surgeon removes a small section of the lamina to relieve compression on the nerve. The remaining spinal bones are connected back together with titanium metal rods and screws.

The skin incision is in the midline of the back of the neck and is about 3 to 4 inches long. The paraspinal muscles are then elevated from multiple levels. Removal of the lamina. A high-speed burr can be used to make a trough in the lamina on both sides right before it joins the facet joint. The lamina with the spinous process can then be removed as one piece (like a lobster tail). Removal of the lamina and spinous process allows the spinal cord to float backwards and gives it more room.

Cervical laminectomy resulted in the greatest increase in global cervical ROM. Resection of the intraspinous and supraspinous ligaments [ISLs).ISLs at C2-3 and C7-T1 increased segmental ROM at these specific levels to a similar extent that laminectomy increased ROM at each cervical level. This segmental ROM may contribute to pain or postprocedural deformity and highlights the importance of the ISLs at the terminal ends of the cervical open door laminoplasty (ODL) 2).

Cervical laminectomy complications.

Prone, some use pin head holder

a) C-arm

b) high speed drill

  1. implants: cervical lateral mass screws and rods if fusion is being done

4. neuromonitoring: some surgeons used SSEP/MEP: Use of intra-op EP monitoring during a routine surgery for CSM or cervical radiculopathy is not recommended as an indication to alter the surgical plan or administer steroids since this paradigm has not been observed to reduce the incidence of neurologic injury (Level D Class III).

5. consent (in lay terms for the patient—not all-inclusive):

a) procedure: surgery through the back of the neck to remove the bone over the compressed spinal cord and nerves and possibly to place screws and rods to fuse the boned together

b) alternatives: nonsurgical management, surgery from the front of the neck, posterior surgery without fusion, laminoplasty

c) complications: nerve root weakness (C5 nerve root is the most common), may not relieve symptoms, further surgery may be needed, possible seizures with MEPs. If fusion is not done, there is a risk of progressive bone slippage, which would require further surgery.

Posterior cervical decompression and fusion.

Posterior fossa decompression for Chiari type 1 deformity.


Hong-Wan N, Ee-Chon T, Qing-Hang Z. Biomechanical effects of C2-C7 intersegmental stability due to laminectomy with unilateral and bilateral facetectomy. Spine (Phila Pa 1976). 2004 Aug 15;29(16):1737-45; discussion 1746. PubMed PMID: 15303016.

Healy AT, Lubelski D, West JL, Mageswaran P, Colbrunn R, Mroz TE. Biomechanics of open-door laminoplasty with and without preservation of posterior structures. J Neurosurg Spine. 2016 May;24(5):746-51. doi: 10.3171/2015.7.SPINE15229. Epub 2016 Jan 22. PubMed PMID: 26799115.
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