Computed tomography-based classification of axis vertebra: choice of screw placement.

PURPOSE: The purpose of the study was to: (1) introduce a new CT-based parameter: free facet area and provide its normative data; (2) standardize the method of measuring isthmus width and height of the axis vertebra; (3) propose a new grading system to predict the difficulty in inserting transarticular and C2 pedicle screws. METHODS: Spiral CT scans of 47 adult dry axis vertebrae were studied. The methods of measuring isthmus width, isthmus height and free facet area are described. RESULTS: The mean isthmus width was 5.04 mm on the right side and 5.42 mm on the left side. The mean isthmus height was 5.21 mm on the right side and 5.45 mm on the left side. Mean free facet area was 61.23 % on the right side and 70.18 % on the left side. A novel grading system is proposed on the basis of these three parameters. As per this grading system, 40.4 % of the sides were found to be difficult for transarticular and 24.5 % sides for C2 pedicle screw insertion (total score 2, 3, 4). A Management protocol is suggested on the basis of the grading system. CONCLUSION: Inserting a transarticular screw was more frequently difficult as compared to pedicle screw. A new CT-based parameter (free facet area) and an efficient grading have been proposed to help surgeons choose the appropriate screw options, appreciate the complex anatomy of this region and compare data across various studies.

Corpus callosum arteriovenous malformation with persistent trigeminal artery.

A 13-year-old boy presented with an intracerebral haematoma secondary to a large corpus callosal arteriovenous malformation (AVM) with an associated persistent trigeminal artery, and was treated with Gamma-Knife Radiosurgery for the AVM. This report discusses the embryological basis, radiological features and various classifications of this rare vascular anomaly.

Distal myopathy with rimmed vacuoles: report on clinical characteristics in 23 cases.

BACKGROUND: Distal myopathy with rimmed vacuoles (DMRV) is an autosomal recessive (AR) myopathy characterized clinically by the preferential involvement of the tibialis anterior and has been reported predominantly in the Japanese population. MATERIALS AND METHODS: A case series of DMRV patients seen over a period of 3 years at a tertiary national referral center for neurological disorders in south India. RESULTS: We describe the clinical characteristics, muscle magnetic resonance imaging (MRI) findings and classical histopathological feature in 23 patients. There were 12 men and 11 women. Mean age of onset was 27.04 +/- 6.35 years (10-39 years). Onset was in the second or third decade in a majority. Mean age at presentation was 33.95 +/- 6.35 years (25-48 years). Mean duration of illness was 6.74 +/- 4.8 years (1-18 years). Consanguinity was reported in eight (34.8%) patients. The predominant and initial manifestation was bilateral foot drop in all patients. Muscle MRI demonstrated classical involvement of the anterior compartment muscles of the lower legs and the posterior compartment muscles of the thighs and the quadriceps was normal in all. Muscle histopathology showed numerous fibers containing rimmed vacuoles. Necrotic fibers or phagocytosis or regenerating fibers were rarely noted or were absent. CONCLUSIONS: DMRV is a rare AR myopathy. The disorder presents as progressive foot drop and hence has many differential diagnoses. It is easily mistaken as neuropathy of hereditary nature and hence it is extremely important to recognize the preferential muscle involvement and characterize the phenotype. This is the first report from India with patients having characteristic phenotype of Nonaka's/AR hereditary inclusion body myopathy with quadriceps sparing, and all were confirmed by histopathology.

Marchiafava-Bignami disease: Two cases with magnetic resonance imaging and positron emission tomography scan findings.

We report two patients with Marchiafava-Bignami disease (MBD). A 38-year-old male with chronic alcohol abuse developed acute onset cerebellar ataxia and altered sensorium. He was diagnosed to have acute form (Type II) of MBD. Magnetic resonance imaging (MRI) showed extensive lesions involving the corpus callosum in its entire extent and also bilateral corona radiata and centrum semiovale. Corpus callosum had heterogeneous signal changes with ring enhancement. Positron emission tomography scan demonstrated reduced cerebral glucose metabolism diffusely over both the cerebral hemispheres. The second patient was 55-year-old male with chronic alcohol intake developed acute onset vomiting followed by behavioral abnormalities and altered sensorium. MRI showed diffuse lesion involving entire corpus callosum with suggestion of necrosis. Both the patients subsequently recovered, the first patient is back to his previous occupation and the second patient could be rehabilitated with some lighter work in his previous work place. Functional brain imaging may help to understand the pathogenesis of acute MBD and possibly the behavioral manifestations.

Can the position of the vertebral artery be predicted on a lateral view X-ray of the craniovertebral junction? A radiological anatomy study.

BACKGROUND: The most feared complication while inserting C2 screws is vertebral artery injury. This article proposes predicting the position of the vertebral artery on a true lateral X-ray of the axis vertebra from the background information acquired from the computed tomography (CT) scan utilizing fluoroscopy. METHODS: Spiral CT scans of 33 C2 vertebrae were performed utilizing a 16-slice CT scanner lateral X-rays of C2 were then obtained before and after painting the vertebral artery grooves with barium. The space available for transarticular and C2 pedicle screw insertion above the vertebral artery groove in the isthmus was then calculated as a ratio for both X-rays and CT scans. RESULTS: There was no statistically significant difference between the (mean) ratios calculated by CT scan and X-rays regarding the space available for transarticular and C2 pedicle screw insertion (left side: 0.3894 vs 0.3897; right side: 0.3892 vs 0.3925; P > 0.05). The Kappa test revealed that CT scan and X-ray findings were in agreement in majority of the bones (left side: n = 24, 72.7%, right side: n = 22, 73.3%; P < 0.05). CONCLUSION: A thorough understanding of a true lateral view X-ray based on background information extracted from three dimensional CT scans helps predict the highest point of the vertebral artery groove. This proves useful for placement of C2 transarticular and pedicle screws during regular "open" and "minimally invasive" spine surgery.

Morphometric and radiological assessments of dimensions of Axis in dry vertebrae: A study in Indian population.

BACKGROUND: The technique of intralaminar screw placement for achieving axis (C2) fixation has been recently described. The purpose of the study was to provide the morphometric and radiological measurements in Indian population and to determine the feasibility of safe translaminar screw placement in this population. To the best of our knowledge there is no study (cadaveric or radiological) done in Indian population to detect suitability of axis bone for laminar screw fixation. MATERIAL AND METHODS: 38 dry axis vertebrae from adult South Indian population were subjected to morphometric measurement and CT scan analysis. Height of posterior arch, midlaminar width(bilateral) in upper 1/3(rd), middle 1/3(rd) and lower 1/3(rd) were measured using high precision Vernier Calipers. Each vertebra was subjected to a spiral CT scan (Philips brilliance 16 slice) thin 0.5 mm slices were taken and reconstruction was done in coronal and sagittal plane. Analysis was done on a CT work station. Using axial slices, sagittal cuts were reconstructed in plane perpendicular to the lamina at the mid laminar point and upper-middle and lower 1/3(rd) width of the lamina measured. Height of the posterior arch was measured in the sagittal plane. Intralaminar angle was measured bilaterally. RESULTS: Middle 1/3(rd) lamina was the thickest portion (mean 5.17 mm +/- 1.42 mm). A total of 32 (84.2%) specimen were having midlaminar width in both lamina greater than 4 mm, however only 27 (71%) out of them had spinous process more than 9 mm. CT scan measurement in middle and lower 1/3(rd) lamina was found to be strongly correlated with the direct measurement. CONCLUSION: There is high variability in the thickness of the C2 lamina. As compared to western population, the axis bones used in the present study had smaller profiles. Hence the safety margin for translaminar screw insertion is low.