Introduction

Deep pelvic masses and abscesses are a challenge for percutaneous intervention due to vital organs that may prevent safe access. Multiple approaches have been described, such as transabdominal, anterolateral extraperitoneal, transosseous, transgluteal, and transperineal. These have all been proven to be safe and effective for tissue biopsy, aspiration, and drainage.

This exhibit will explore the relevant anatomy, technique, possible complications, and technique modifications of CT guided biopsy and drainage via the transgluteal route through the greater sciatic foramen, as well as abscess drainage via the transperineal approach.

Anatomy

Knowledge of the pelvic anatomy is of the utmost importance due to susceptibility of injury to vasculature, nerves, bowel, and gynecologic or urologic structures.

The greater sciatic foramen is a space in the posterolateral pelvis bound posteriorly by the sacrum, anteriorly by the ischium, superiorly by the ilium, and inferiorly by the sacrospinous ligament. Contents of the greater sciatic notch include the piriformis muscle, vessels from the internal iliac system, and nerves of the sacral plexus.

The piriformis muscle originates from the anterior surface of the sacrum and exits the greater sciatic foramen to insert on the greater trochanter of the femur. Superior to the piriformis muscle exits the superior gluteal vessels and nerves; inferior to the muscle exits the inferior gluteal vessels and nerves, internal pudendal vessels and nerve, sciatic and posterior femoral cutaneous nerves, and the nerves to the obturator internus and quadratus femoris.   The sacrospinous ligament is the inferior border of the greater sciatic foramen. The major vessels and nerves lie superior to this level, crossing anterior to the piriformis muscle. Ensuring that the needle or catheter traverses the sacrospinous ligament decreases the chance of inadvertent injury to these vessels and nerves.

Technique

Transgluteal CT guided biopsy and drainage shares many of the same principles as percutaneous intervention by any other route. This includes the appropriate indications, contraindications and patient preparation. However, aspects unique to the transgluteal approach include patient positioning, route planning, and equipment.

Proper patient positioning and maintenance of such is vital for a successful procedure. The optimum position is prone if the patient is able to tolerate it. Patients who are recent post-operative, those with relatively new abdominal wounds, or who are on a mechanical ventilator pose a challenge. These patients can be placed in an oblique or lateral decubitus position. However, they must be able to maintain that position. Hence, pain control is very important. Local anesthesia is used in all patients; conscious sedation or general anesthesia should be considered in select cases. Devices such as pillows or straps can also be used as appropriate to secure the patients position.

Although the safest route through the greater sciatic foramen is at the level of the sacrospinous ligament as close to the lateral edge of the sacrum as possible, some lesions require more superior or lateral course. This is safe as long as all vital structures are identified and are avoided.

Potential complications

Potential complications can be prevented with meticulous technique and careful route planning. These include pain, hemorrhage, nervous system injury, bowel injury, catheter malposition, and injury to other vital structures (gynecologic and urologic).

CT-guided Transgluteal and Transperineal Percutaneous Biopsy and Drainage of Deep

Pelvic Structures: Anatomy, Indications, Technique, and Potential Complications T M Nguyen, W D Boswell, P A Nedumaran, H G Pimenta, F M Wu, V Duddalwar

Department of Radiology, University of Southern California, Los Angeles, California 90033

Figure 1: Normal anatomy. Transverse CT images through the pelvis with intravenous and oral contrast. Piriformis muscle (p), gluteal vessels (arrows), bowel (b), sacrospinous ligament (arrowheads).

Figure 3: Drainage catheter placement. Presacral abscess (a) in a patient with rectal carcinoma status post low anterior resection. Patient is placed in a right lateral decubitus due to recent surgery and colostomy. A drainage catheter is place via the left greater sciatic foramen by a trochar technique. Notice the catheter traverses the sacrospinous ligament just lateral to the lateral edge of the sacrum, avoiding vessels and nerves.

Modifications

Technique modifications may be necessary to successfully target a lesion. These include CT fluoroscopy, angling of the CT gantry, use of a curved needle through a coaxial system, injection of saline to displace vital structures, and use of a blunt needle.

CT fluoroscopy may be useful for the exact positioning of a needle. It has the potential to reduce procedure time and provide more accurate positioning, but can increase radiation exposure to both the patient and the operator. Angling the CT gantry is useful in targeting a lesion cephalad to the sacrospinous ligament. It is technically more difficult, however, to keep the needle in the exact same angle as the gantry. Use of a curved needle allows an additional option for difficult to access lesions.

Techniques to displace vital structures may be useful to access a lesion. The degree of displacement is a function of the mobility of the structure. Injecting sterile saline adjacent to a structure may displace it enough to allow adequate access. This technique may obscure the normal anatomy and/or target making the procedure more difficult. Therefore it is crucial to inject slowly and check progress often.

The use of a blunt needle (Inter-V Hawkins Blunt Needle, Medical Device Technologies, Inc, Gainesville, FL) is another technique that may improve access to a lesion. This system is supplied with a coaxial hollow needle and both sharp and blunt inner stylets. Torquing forces can be applied to the system with the blunt stylet in place in an attempt to displace the structure. In addition, the system can be advanced with the blunt stylet in place allowing blunt dissection of soft tissue, decreasing the risk of injury to vascular or nervous system structures.

Transperineal approach

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A coaxial biopsy system is preferred to prevent unnecessary repeat punctures and repositioning. Drainages can be performed by the Seldinger technique, which offers more control and precision. A trochar technique is useful for larger collections.

Figure 2: Coaxial needle biopsy. (A) Transverse CT image through the pelvis in a rectal carcinoma patient status post previous low anterior resection, found to have abnormal soft tissue adjacent to the anastamotic site (arrow). (B, C) Patient is positioned right anterior oblique and a coaxial needle system advanced through the greater sciatic foramen at the level of the sacrospinous ligament to biopsy this tissue.

A B C

Figure 4: Techniques to displace structures. (A) An enlarged retroperitoneal lymph node (arrow) medial to the psoas muscle. Descending colon (c) lies along the course of proposed biopsy route. (B) A Hawkins needle is positioned with the sharp inner stylet, tip adjacent to the segment of colon (c) to be displaced. (C) Sterile saline in injected through the outer needle; the segment of colon is displaced anteriorly. (D) The blunt needle is then placed through the hollow needle and advanced through the retroperitoneal fat. Lateral force is then applied to the needle system, further displacing the segment of colon anteriorly. A biopsy needle can now be advanced to sample the lymph node.

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c c

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C D

Figure 5: Malpostioned catheter. (A) Prone CT images through the pelvis in a patient status post sigmoidectomy with a contained post-surgical anastamotic leak (arrow). Bowel (arrowhead). (B) Drainage catheter placed via the greater sciatic notch, malpositioned into the bowel. (C) Drainage catheter repositioned into presacral collection.

Figure 6: Hemorrhage. (A) Post procedure image after drainage catheter placement via the greater sciatic notch. The ipsilateral muscles are enlarged due to hematoma. (B) Digital subtraction angiogram from the ipsalateral internal iliac artery shows pseudoaneurysm of inferior gluteal artery. Embolic coils were placed. (C) Post-embolism angiogram reveals a successful embolisation.

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Figure 7: Transperineal drainage. (A) Transverse CT image in a patient status post proctocolectomy shows a large presacral fluid collection (f). The collection is inaccessible from an anterior approach. Although accessible through the greater sciatic notch, the lack of any vital midline structures from patient’s proctocolectomy favors a midline transperineal approach. (B) Saggital reconstruction shows a drainage catheter in the fluid collection from a midline perineum puncture.

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ReferencesButch RJ, Mueller PR, Ferrucci JT, et al. Drainage of Pelvic Abscesses through the Greater Sciatic Foramen. Radiology

1986; 158:487-491.Gupta S, Nguyen HL, Morello FA, et al. Various Approaches for CT-guided Percutaneous Biopsy of Deep Pelvic Lesions: Anatomic and Technical Considerations. RadioGraphics 2004; 24:175-189. Harishinghani MG, Gervais DA, Hahn PF, et al. CT-guided Transcluteal Drainage of Deep Pelvic Abscess: Indications,

Technique, Procedure-related Complications,and Clinical Outcome. RadioGraphics 2002; 22:1353-1367.Harishinghani MG, Gervais DA, Maher MM, et al. Transgluteal Approach for Percutaneous Drainage of Deep Pelvic

Abscesses: 154 Cases. Radiology 2003; 228:701-705.