Variability in the size of the retroperitoneal oblique corridor: A magnetic resonance imaging-based analysis.

BACKGROUND: A minimally invasive approach to the L2-S1 disc spaces through a single, left-sided, retroperitoneal oblique corridor has been previously described. However, the size of this corridor varies, limiting access to the disc space in certain patients. Here, the authors retrospectively reviewed lumbar spine magnetic resonance imaging (MRI) in 300 patients to better define the size and variability of the retroperitoneal oblique corridor. METHODS: Lumbar spine MRI from 300 patients was reviewed. The size of the retroperitoneal oblique corridor from L2-S1 was measured. It was defined as the (1) distance between the medial aspect of the aorta and the lateral aspect of the psoas muscle from L2-L5 and (2) the distance between the midpoint of the L5-S1 disc and the medial aspect of the nearest major vessel on the left at L5-S1. In addition, the rostral-caudal location of the iliac bifurcation was measured. RESULTS: The size of the retroperitoneal oblique corridor at L2/3, L3/4, L4/5, and L5/S1 was, respectively, 17.3 ± 6.4 mm, 16.2 ± 6.3 mm, 14.8 ± 7.8 cm, and 13.0 ± 8.3 mm. The incidence of corridor size <1 cm at L2/3, L3/4, L4/5, and L5/S1 was 10.3%, 16.0%, 30.0%, and 39.3%, respectively. The iliac bifurcation was most commonly found behind the L4 vertebral body (n = 158, 52.67%) followed by the L4/5 disc space (n = 74, 24.67%). CONCLUSION: The size of the retroperitoneal oblique corridor diminishes in a rostral-caudal direction, often limiting access to the L4/5 and L5/S1 disc spaces.

Variation in Psoas Muscle Location Relative to the Safe Working Zone for L4/5 Lateral Transpsoas Interbody Fusion: A Morphometric Analysis.

BACKGROUND: The safe working zone for lateral access to the L4/5 disc space has been said to lie in the anteroposterior (AP) midpoint of the disc space due to the location of the femoral nerve at that level. However, the AP location of the psoas muscle (and thus the lumbosacral plexus within) at L4/5 is variable. A psoas muscle lying excessively anteriorly at the L4/5 disc space may preclude safe access to the L4/5 disc space from a lateral transpsoas approach. METHODS: Lumbar spine magnetic resonance imaging (MRI) for 300 consecutive patients at the authors' institution were reviewed retrospectively. The AP distance between the ventral aspect of the thecal sac and the dorsal aspect of the psoas muscle at L4/5 was measured, as was the AP diameter of the L4/5 disc space. RESULTS: The dorsal aspect of the psoas muscle at L4/5 was most commonly found dorsal to the ventral aspect of the thecal sac (zone P, N = 145; 48.3%), whereas it was found at the junction of zones IV/P in 37 patients (12.3%), in zone IV in 85 patients (28.3%), in zone III in 29 patients (9.7%), and in zone II in 4 patients (1.3%). CONCLUSIONS: The location of the psoas muscle in relation to the L4/5 disc space is somewhat variable. In 11% of patients, the dorsal-most aspect of the psoas muscle was located within zones II or III, likely precluding safe access to the L4/5 disc space from a lateral transpsoas approach.

Spinal Schwannoma and Meningioma Mimicking a Single Mass at the Craniocervical Junction Subsequent to Remote Radiation Therapy for Acne Vulgaris.

BACKGROUND: Schwannomas and meningiomas are relatively common tumors of the nervous system. They have been reported in the literature as existing concurrently as a single mass, but very rarely have they been shown to present at the craniocervical junction. CASE DESCRIPTION: We present a rare and interesting case of a patient previously treated with radiation therapy for acne vulgaris and who presented to us with a concurrent schwannoma and meningioma of the craniocervical junction mimicking a single mass. CONCLUSIONS: These tumors can be solitary or mixed masses, and are known to be associated with certain disease processes such as long-term sequelae of radiation therapy and neurofibromatosis type 2. The precise mechanism behind the formation of these tumors is unknown; however, molecular cues in the tumor microenvironment may play a role.

Surgical approaches to meningiomas of the lateral ventricles.

BACKGROUND: Intraventricular meningiomas account for 0.5-3% of all intracranial meningiomas. The majority occur in the atrium of the lateral ventricle. Surgical experience with intraventricular meningiomas is rare in the literature, and several surgical approaches exist. METHODS: Between 1987 and 2007, 13 patients underwent resection of intraventricular meningiomas. All patients had tumors of the lateral ventricles. These patients were retrospectively identified and their records reviewed. RESULTS: Eleven tumors were found in the atrium, one in the frontal horn, and one in the body of the lateral ventricle. In 9 of 13 cases, the tumor occurred in the left lateral ventricle. Patients commonly presented with headache and cognitive difficulties. A visual field deficit was noted preoperatively in one patient. Four patients underwent preoperative angiography, but no patients underwent embolization. Gross total resection was achieved in all cases: 6 via a middle temporal gyrus approach, 5 via a superior parietal lobule approach, and 2 via a transcallosal approach. Image-guided stereotaxis was used in 6 cases. Pathology was benign in 12 of 13 cases; atypical features were identified in one case. There was no operative mortality, and no patients showed evidence of recurrence. Postoperatively, 3 patients developed new cognitive-linguistic deficits that subsequently resolved. One of these patients developed a new visual field deficit after surgery. CONCLUSIONS: Several approaches are available for the surgical treatment of intraventricular meningiomas. Tumor location, extension, and laterality drive the selection algorithm for these approaches. Preoperative angiography is rarely useful, and surgical cure is the rule.