The reliability of computerized tomographic detection of the Onodi (Sphenoethmoid) cell.

Optic nerve injury is a devastating potential complication of endoscopic sinus surgery. Anatomic variations of the posterior ethmoid sinus are certainly contributing factors. In the most well described posterior ethmoid anatomical variant, the sphenoethmoid or Onodi cell, the optic nerve is placed at risk during sinus surgery. Improving preoperative and intraoperative identification of the sphenoethmoid (Onodi) cell could decrease the risk of optic nerve injury. The purpose of this investigation was to assess the reliability of computerized tomography (CT) in detecting the sphenoethmoid (Onodi) cell, and further our understanding of this clinically relevant anatomic variant. A total of 41 sinonasal complexes from 21 human adult cadaveric heads were studied with a standard coronal and axial plane CT, and subsequent endoscopic dissection. The prevalence of the sphenoethmoid (Onodi) cell was determined by CT and endoscopic dissection, as were other anatomic characteristics of the posterior ethmoid anatomy. In our study, CT identified a sphenoethmoid (Onodi) cell in 3/41 (7%) of the sphenoethmoid complexes. However, anatomic dissection identified a sphenoethmoid (Onodi) cell in 16/41 (39%) complexes. Coronal orientation of the anterior sphenoid wall was never associated with a sphenoethmoid (Onodi) cell. Conversely, oblique or horizontal orientations were present in all cases of sphenoethmoid (Onodi) cells. Current CT scanning protocols for the paranasal sinuses did not reliably detect the Onodi cell. Endoscopic dissection indicates that the sphenoethmoid (Onodi) cell is a more frequent anatomic variant than previously appreciated. Awareness of anterior sphenoid wall orientation may assist surgeons in identifying the Onodi cell, thereby reducing the risk of optic nerve trauma.

Determination of 60% or greater carotid stenosis: a prospective comparison of magnetic resonance angiography and duplex ultrasound with conventional angiography.

The morbidity and cost of conventional angiography (CA) have focused recent efforts in cerebrovascular imaging upon the exclusive use of noninvasive techniques. Our purpose was to prospectively evaluate carotid magnetic resonance angiography (MRA) and to compare its accuracy with color-flow duplex (CFD). Fifty patients were prospectively evaluated with CA and MRA after clinical and CFD findings indicated the need for carotid angiography. CFD measurements of peak systolic velocity (PSV) and end-diastolic velocity (EDV) were made. MRA results were categorized as 0%-39%, 40%-59%, 60%-79%, or 80%-99% stenosis or occluded. Determination of percent carotid stenosis by CA was made as in the North American Symptomatic Carotid Endarterectomy Trial (NASCET). Using receiver operating characteristic (ROC) curves, the probability of correctly predicting a > or =60% stenosis using various CFD thresholds and MRA was assessed. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) in determining > or =60% stenosis were estimated. For MRA the sensitivity was 85% (95% Confidence Interval [CI] = 69%-94%), specificity 70% (CI = 56%-81 %), PPV 68% (CI = 53%-80%), and NPV 86% (CI = 72%-94%). For CFD the sensitivity was 89% (CI = 74%-96%), specificity 93% (CI = 82%-98%), PPV 89% (CI = 74%-96%), and NPV 93% (CI = 82%-98%). When MRA and CFD results were concordant (n = 64), the sensitivity was 100% (CI = 89%-100%), specificity 95% (CI = 81%-99%), PPV 94% (CI = 77%-99%), and the NPV was 100% (CI = 92%-100%). The area under the ROC curve for CFD was 95%, compared to 83% for MRA (p = 0.0005). We conclude that the low specificity of MRA precludes its use as the definitive imaging modality for carotid stenosis. The 93% specificity of CFD alone warrants its consideration as a definitive carotid imaging study. By ROC curve analysis, CFD offers superior accuracy to MRA. Our data support noninvasive preoperative carotid imaging for detecting a threshold stenosis of > or =60% whether CFD is used alone, or in combination with the selective use of MRA.

Intratentorial lipomas with Meckel's cave and cerebellopontine angle extension.

An unusual case of bilateral intratentorial lipomas with extension into Meckel's caves and the cerebellopontine angle is described. Surgical and histopathologic correlation demonstrate that the lipoma encased the trigeminal nerve in Meckel's caves. The origin of the lipoma from the anteromedial margins of the tentorium is discussed and correlated with a recently proposed theory for the development of intracranial lipomas.

Radiologic-pathologic correlation. Diffuse pontine astrocytoma.

This case demonstrated the classic gross, pathologic, CT, and MR findings of pontine astrocytoma. The role of functional brain imaging in identifying regrowth of tumor was illustrated and the differential diagnosis of a brain stem lesion summarized.

Understanding the radiology of intracranial primitive neuroectodermal tumors from a pathological perspective: a review.

The concept of primitive neuroectodermal tumors (PNETs) has been controversial since its introduction in 1973. Understanding these tumors is important for the neuroradiologist, because certain radiological features may suggest their diagnosis. A review of the PNET concept, as well as the different types of intracranial PNETs is made, using as a framework the cytogenesis of the brain. Emphasis is given to pathologic features, as they ultimately determine radiologic findings. Supratentorial PNETs are large, bulky, heterogeneous masses with "cystic" (necrotic) areas, calcification, and very little edema. Infratentorial PNETs are generally less heterogeneous, but the larger tumors tend to be more cystic, necrotic, and calcific, resembling supratentorial PNETs.