Intraoperative ultrasound in neurosurgery [Neurosurgery Wiki]

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====== Intraoperative ultrasound in neurosurgery ======

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[[Intraoperative]] [[ultrasound]] (IOUS) is an invaluable [[tool]] in neurosurgery, offering real-time imaging during procedures. It provides surgeons with dynamic, detailed insights into brain and spinal cord anatomy, enabling better decision-making during surgeries like tumor resection, hematoma evacuation, or cyst aspiration. Its portability, cost-effectiveness, and lack of ionizing radiation make it a versatile adjunct to more traditional imaging modalities like MRI and CT.



===== Advantages =====

- **Real-time Imaging**: Immediate feedback for the surgeon, improving accuracy and confidence.
- **No Ionizing Radiation**: Unlike intraoperative CT or fluoroscopy, ultrasound does not expose patients or staff to radiation.
- **Portable and Cost-effective**: More affordable and accessible compared to intraoperative MRI.
- **Dynamic Imaging**: Allows visualization of physiological changes during surgery, such as tumor collapse or residual tissue.

===== Limitations =====

1. **Operator Dependency**: Requires skill and experience for accurate interpretation.
2. **Limited Penetration**: Ultrasound struggles with deep or highly calcified lesions due to signal attenuation.
3. **Image Quality**: Lower resolution compared to intraoperative MRI.
4. **Acoustic Barriers**: Air, bone, and certain instruments may interfere with imaging.

===== Techniques and Probes =====

- **B-mode Ultrasound**: Most commonly used; provides 2D grayscale images for structural analysis.
- **Doppler Ultrasound**: Evaluates blood flow in vessels, helping to avoid vascular injury.
- **High-frequency Probes**: Used for superficial lesions requiring high-resolution imaging.
- **Low-frequency Probes**: Better suited for deeper structures due to improved penetration.

===== Future Directions =====

1. **Fusion Imaging**: Combining IOUS with preoperative MRI/CT for better orientation and precision.
2. **3D Ultrasound**: Advances in 3D imaging can improve the surgeon’s spatial understanding of complex anatomy.
3. **Artificial Intelligence**: Integration of AI could enhance image interpretation and tumor segmentation.
4. **Elastography**: Investigates tissue stiffness, aiding in differentiation between tumor and normal brain tissue.

===== Conclusion =====

Intraoperative ultrasound is a powerful adjunct in neurosurgery, enabling safer and more effective interventions. While it has limitations, ongoing technological advancements continue to improve its utility and accuracy, making it an essential tool in modern neurosurgical practice.
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The use of [[intraoperative techniques]] to detect [[residual tumor]]s has recently become increasingly important. Intraoperative MRI has long been considered the gold standard; however, it is not widely used because of high equipment [[cost]]s and long acquisition times.

Consequently, real-time [[intraoperative ultrasound]] (ioUS), which is much less expensive than MRI, has gained popularity
((Aibar-Duran JA, Salgado-López L, Anka-Tugbiyele MO, Mirapeix RM, Gallardo Alcañiz A, Patino Alvarado JD, Rico Pereira M, Rodríguez Rodríguez R, Munoz-Hernandez F, de Quintana-Schmidt C. Navigated intraoperative ultrasound in neuro-oncology: volumetric accuracy and correlation with high-field MRI. J Neurosurg. 2024 Jan 5:1-10. doi: 10.3171/2023.10.JNS231244. Epub ahead of print. PMID: 38181499.))
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The first description of the application of [[intraoperative ultrasound]] in [[neurosurgery]] was in [[1978]] with Reid
((Reid, M.H., Ultrasonic visualization of a cervical cord cystic astrocytoma. AJR Am J Roentgenol, 1978. 131(5): p. 907-8.)).

Intraoperative ultrasound (iUS) allows the generation of real-time data sets during surgical interventions.

Although the quality of the gray-scale US image before tumor resection is excellent, little information is gained in terms of perfusion of the lesion, even with the aid of Doppler US, and tumor margins are not always clearly detectable with B-mode ioUS only.

see [[3D ultrasound]]

===== Indications =====

[[Intraoperative ultrasound indications]]


====Types====

[[Contrast enhanced ultrasound]]

[[Intraoperative Doppler ultrasound]]

[[Linear array intraoperative ultrasound]] (lioUS)

[[Curved or sector array ultrasound]](cioUS)

[[Ultrasonic aspiration]].

==== BraTioUS database ====
[[BraTioUS]] database

===== Case series =====

A [[prospective]] study of adult patients who underwent surgery for [[intraaxial]] brain tumors between November 2017 and October 2020 was performed. Navigated [[intraoperative ultrasound]] (nioUS) of the brain was used to guide [[tumor resection]] and to detect the presence of residual disease. Both convex (5-8 MHz) and linear array (6-13 MHz) probes were used. [[Tumor volume]] and residual disease were measured with nioUS and compared with MR images. A linear regression model based on a machine learning pipeline and a Bland-Altman analysis were used to assess the accuracy of nioUS versus MRI.

Eighty patients (35 females and 45 males) were included. The mean age was 58 years (range 25-80 years). A total of 88 lesions were evaluated; there were 64 (73%) gliomas, 19 (21.6%) metastases, and 5 (5.7%) other tumors, mostly located in the frontal (41%) and temporal (27%) lobes. Most of the tumors (75%) were perfectly visible on ioUS (grade 3, Mair grading system), except for those located in the [[insula]]r lobe (grade 2). The regression model showed a nearly perfect correlation (R2 = 0.97, p < 0.001) between preoperative tumor volumes from both MRI and nioUS. Ultrasonographic visibility significantly influenced this correlation, which was stronger for highly visible (grade 3) tumors (p = 0.01). For residual tumors, the correlation between postoperative MRI and nioUS was weaker (R2 = 0.78, p < 0.001) but statistically significant. The Bland-Altman analysis showed minimal bias between the two techniques for pre- and postoperative scenarios, with statistically significant results for the preoperative concordance.

The authors' findings show that most brain tumors are well delineated by nioUS and almost perfectly correlated with MRI-based measurements both pre- and postoperatively. These data support the hypothesis that nioUS is a reliable intraoperative technique that can be used for real-time monitoring of brain tumor resections and to perform volumetric analysis of residual disease
((Aibar-Duran JA, Salgado-López L, Anka-Tugbiyele MO, Mirapeix RM, Gallardo Alcañiz A, Patino Alvarado JD, Rico Pereira M, Rodríguez Rodríguez R, Munoz-Hernandez F, de Quintana-Schmidt C. Navigated intraoperative ultrasound in neuro-oncology: volumetric accuracy and correlation with high-field MRI. J Neurosurg. 2024 Jan 5:1-10. doi: 10.3171/2023.10.JNS231244. Epub ahead of print. PMID: 38181499.)).
===2017===
Brock et al., analyzed prospectively 49 patients with [[Chiari type 1 deformity]], operated at the Hospital das Clinicas, College of Medicine, University of São Paulo. Patients underwent decompressive surgery with or without opening of the duramater after [[intraoperative ultrasonography]] measuring flow rate. A value of 3cm/s was considered a cut-off. Quality of life before and after surgery and the improvement of [[neck pain]] and headache were evaluated.

Among 49 patients enrolled, 36 patients (73%) had CSF flow above 3 cm/s and did not undergo duraplasty. In 13 (27%) patients with initial flow <3 cm/s, a dural opening was performed together with duraplasty. All patients improved comparing pre and post operative scores and all clinical parameters evaluated did not differ between both surgical groups. Patients submitted to bone decompression alone had fewer complication rate.

Intraoperative USG with measurement of CSF allows the proper selection of patients with CM that can have a less invasive surgery with bone decompression without duraplasty
((Brock RS, Taricco MA, de Oliveira MF, de Lima Oliveira M, Teixeira MJ,
Bor-Seng-Shu E. Intra Operative Ultrasonography for Definition of Less Invasive
Surgical Technique in Patients with Chiari Type I Malformation. World Neurosurg. 
2017 Feb 9. pii: S1878-8750(17)30152-3. doi: 10.1016/j.wneu.2017.02.003. [Epub
ahead of print] PubMed PMID: 28192262.
)).
===2016===
A retrospective review of the medical charts of all pediatric patients who underwent neurosurgical treatment of a tumor between August 2009 and July 2015 at [[Albany]] Medical Center. Included were patients who were aged ≤ 21 years, who underwent brain or spinal tumor resection, for whom IOUS was used during the tumor resection, and for whom postoperative MRI (with and without contrast) was performed within 1 week of surgery. 

Sixty-two patients met inclusion criteria for the study (33 males, mean age 10.0 years). The IOUS results very significantly correlated with postoperative MRI results (φ = 0.726; p = 0.000000011; negative predictive value 86.3% [95% CI 73.7%-94.3%]). These results exemplify a 71% overall gross-total resection rate and 80% intended gross-total resection rate with the use of IOUS (i.e., excluding cases performed only for debulking purposes). 

The use of IOUS may play an important role in achieving a greater extent of resection by providing real-time information on tumor volume and location in the setting of brain shift throughout the course of an operation. The authors support the use of IOUS in pediatric CNS tumor surgery to improve clinical outcomes at low cost with minimal additional operating-room time and no identified additional risk
((Smith H, Taplin A, Syed S, Adamo MA. Correlation between intraoperative
ultrasound and postoperative MRI in pediatric tumor surgery. J Neurosurg Pediatr.
2016 Jul 29:1-7. [Epub ahead of print] PubMed PMID: 27472668.
)).
===2015===
Thirty three patients with small subcortical lesions. The maximum diameter of the lesions ranged between 18 and 30 mm. The depth of the lesion was described as the distance between the cortical surface and most outer point of the lesion. The mean of the depth of the lesions was 10.56 mm ranging between 3.3 and 18.7 mm. Multiple skin staples were used as irremovable skin markers. Before and after dural incision, ultrasound was used to assess the lesion size and location, its relationship with the surrounding tissue and the Doppler function to reveal the blood supply to the lesion. In this study mean craniotomy diameter was 44 mm ranging between 32-55 mm. The location, extent, characteristics and adjacent tissue of the lesion were observed by high frequency ultrasonography during the operation. Kazanci et al. describe a simple, safe and effective method for determining a small [[skin incision]] and [[craniotomy]] combined with intraoperative ultrasound for small [[subcortical]] [[intracranial]] [[lesion]]s for health center that does not have [[Intraoperative magnetic resonance imaging]] and [[navigation]] systems
((Kazanci A, Gurcan O, Gurcay AG, Bozkurt I, Algin O, Turkoglu OF, Bavbek M. A
simple, safe and effective surface marking and targeting method combined with
intraoperative ultrasonography for small subcortical intracranial lesions. J
Neurosurg Sci. 2015 Jul 14. [Epub ahead of print] PubMed PMID: 26173480.)).

===2012===
22 Patients harboring an intracerebral high-grade tumor were retrospectively included in this study (14 primary tumors, 8 metastases). 14 of them had a perilesional edema equal or greater to lesion volume, 3 had previously received radiotherapy. Following macroscopic tumor debulking, the small (11 × 31 mm) L15 - 7io (Philips, Bothell, USA) high-frequency probe (7 - 15 MHz) was introduced into the resection cavity and its walls were meticulously scanned to search for tumor remnants. Postoperative MR scan was evaluated by a board-certified independent neuroradiologist, who assessed the EOR.

Gross total resection was achieved in 21 patients (95.5 %). One patient had a small tumor remnant (6 × 4 × 3 mm) of a very large (80 × 60 × 74 mm) anaplastic astrocytoma, detected in the postoperative MR scan. A permanent postoperative hemiparesis was diagnosed in one patient with a metastases in the motor area, while the other patients recovered without permanent neurological deficits from the surgery.

The hfioUS probe allowed in this study a precise detection of the tumor and a detailed discrimination between normal, pathological and edematous tissue in all 22 cases
((Serra C, Stauffer A, Actor B, Burkhardt JK, Ulrich NH, Bernays RL, Bozinov O. 
Intraoperative high frequency ultrasound in intracerebral high-grade tumors.
Ultraschall Med. 2012 Dec;33(7):E306-12. doi: 10.1055/s-0032-1325369. Epub 2012
Nov 5. PubMed PMID: 23129521.)).

===== Books =====

[[Intraoperative Ultrasound Books]]