Comparison of a Photon-Counting-Detector CT with an Energy-Integrating-Detector CT for Temporal Bone Imaging: A Cadaveric Study.

BACKGROUND AND PURPOSE: Evaluating abnormalities of the temporal bone requires high-spatial-resolution CT imaging. Our aim was to assess the performance of photon-counting-detector ultra-high-resolution acquisitions for temporal bone imaging and compare the results with those of energy-integrating-detector ultra-high-resolution acquisitions. MATERIALS AND METHODS: Phantom studies were conducted to quantify spatial resolution of the ultra-high-resolution mode on a prototype photon-counting-detector CT scanner and an energy-integrating-detector CT scanner that uses a comb filter. Ten cadaveric temporal bones were scanned on both systems with the radiation dose matched to that of the clinical examinations. Images were reconstructed using a sharp kernel, 0.6-mm (minimum) thickness for energy-integrating-detector CT, and 0.6- and 0.25-mm (minimum) thicknesses for photon-counting-detector CT. Image noise was measured and compared using adjusted 1-way ANOVA. Images were reviewed blindly by 3 neuroradiologists to assess the incudomallear joint, stapes footplate, modiolus, and overall image quality. The ranking results for each specimen and protocol were compared using the Friedman test. The Krippendorff α was used for interreader agreement. RESULTS: Photon-counting-detector CT showed an increase of in-plane resolution compared with energy-integrating-detector CT. At the same thickness (0.6 mm), images from photon-counting-detector CT had significantly lower (P < .001) image noise compared with energy-integrating-detector CT. Readers preferred the photon-counting-detector CT images to the energy-integrating-detector images for all 3 temporal bone structures. A moderate interreader agreement was observed with the Krippendorff α = 0.50. For overall image quality, photon-counting-detector CT image sets were ranked significantly higher than images from energy-integrating-detector CT (P < .001). CONCLUSIONS: This study demonstrated substantially better delineation of fine anatomy for the temporal bones scanned with the ultra-high-resolution mode of photon-counting-detector CT compared with the ultra-high-resolution mode of a commercial energy-integrating-detector CT scanner.

Temporal Bone CT: Improved Image Quality and Potential for Decreased Radiation Dose Using an Ultra-High-Resolution Scan Mode with an Iterative Reconstruction Algorithm.

BACKGROUND AND PURPOSE: Radiation dose in temporal bone CT imaging can be high due to the requirement of high spatial resolution. In this study, we assessed whether CT imaging of the temporal bone by using an ultra-high-resolution scan mode combined with iterative reconstruction provides higher spatial resolution and lower image noise than a z-axis ultra-high-resolution mode. MATERIALS AND METHODS: Patients with baseline temporal bone CT scans acquired by using a z-axis ultra-high-resolution protocol and a follow-up scan by using the ultra-high-resolution-iterative reconstruction technique were identified. Images of left and right temporal bones were reconstructed in the axial, coronal, and Poschl planes. Three neuroradiologists assessed the spatial resolution of the following structures: round and oval windows, incudomallear and incudostapedial joints, basal turn spiral lamina, and scutum. The paired z-axis ultra-high-resolution and ultra-high-resolution-iterative reconstruction images were displayed side by side in random order, with readers blinded to the imaging protocol. Image noise was compared in ROIs over the posterior fossa. RESULTS: We identified 8 patients, yielding 16 sets of temporal bone images (left and right). Three sets were excluded because the patient underwent surgery between the 2 examinations. Spatial resolution was comparable (Poschl) or slightly better (axial and coronal planes) with ultra-high-resolution-iterative reconstruction than with z-axis ultra-high-resolution. A paired t test indicated that noise was significantly lower with ultra-high-resolution-iterative reconstruction than with z-axis ultra-high-resolution (P < .001), with a mean noise reduction of 37% (range, 18%-49%). CONCLUSIONS: The ultra-high-resolution-iterative reconstruction scan mode has similar or slightly better resolution relative to the z-axis ultra-high-resolution mode for CT of the temporal bone but significantly (P < .01) lower image noise, which may enable the dose to be reduced by approximately 50%.

From the archives of the AFIP: superficial gliomas: radiologic-pathologic correlation. Armed Forces Institute of Pathology.

Glial neoplasms that are peripherally located and involve the cortical gray matter are noteworthy because of their predilection to serve as a seizure locus, their amenability to surgical resection, their generally favorable prognosis, and their characteristic imaging features, which facilitate diagnosis before surgery. The smaller lesions include ganglioglioma and dysembryoplastic neuroepithelial tumor. Gangliogliomas contain both neuronal and glial components and occur most commonly in the temporal lobe. Variant forms of gangliogliomas may occur and are related to the different compositions of the underlying cellular population. Gangliocytomas lack glial cells and are located both in the cerebral hemispheres and the cerebellum. Lhermitte-Duclos disease represents a specific type of cerebellar gangliocytoma with dysplastic features and is characterized by a laminar pattern at imaging. Dysembryoplastic neuroepithelial tumors occur predominantly in children and young adults with partial seizures and most commonly arise in the temporal lobe, frequently in combination with cortical dysplasia. Surrounding vasogenic edema is conspicuously absent in both gangliogliomas and dysembryoplastic neuroepithelial tumors. The larger masses in this group include desmoplastic infantile ganglioglioma and pleomorphic xanthoastrocytoma and tend to involve the leptomeninges and cortical territory. Both invoke an intense desmoplastic reaction, which appears as an enhancing soft-tissue component at imaging.

Neoplasms of the spinal cord and filum terminale: radiologic-pathologic correlation.

Intramedullary spinal cord neoplasms are rare, accounting for about 4%10% of all central nervous system tumors. Despite their rarity, these lesions are important to the radiologist because magnetic resonance (MR) imaging is the preoperative study of choice to narrow the differential diagnosis and guide surgical resection. On contrast materialenhanced MR images, intramedullary spinal tumors almost always manifest as expansion of the spinal cord and show enhancement. Syringohydromyelia and cystic lesions are frequently associated with intramedullary tumors. Nontumoral cysts tend to be located at the poles of the tumors and do not enhance on contrast-enhanced MR images, whereas cysts within the substance of the tumor are considered tumoral cysts and typically demonstrate peripheral enhancement. Spinal cord ependymomas are the most common type in adults, and cord astrocytomas are most common in children. Both entities constitute up to 70% of all intramedullary neoplasms. A central location within the spinal cord, presence of a cleavage plane, and intense homogeneous enhancement are imaging features that favor an ependymoma. Intramedullary astrocytomas are usually eccentrically located within the cord, are ill defined, and have patchy enhancement after intravenous contrast material administration. Even with these characteristics, it may not be possible to differentiate these two entities on the basis of imaging features alone. Cord hemangioblastomas are the third most common type of intramedullary spinal tumor. Gangliogliomas commonly extend over more than eight vertebral segments. Paragangliomas and primitive neuroectodermal tumors have an affinity for the filum terminale and cauda equina. Other spinal cord tumors include metastatic disease, which is characterized by prominent cord edema for the size of the enhancing portion, and primary lymphoma.

From the archives of the AFIP. Paragangliomas of the head and neck: radiologic-pathologic correlation. Armed Forces Institute of Pathology.

Paragangliomas of the head and neck are ubiquitous in their distribution, originating from the paraganglia or glomus cells within the carotid body, vagal nerve, middle ear, jugular foramen, and numerous other locations. The typical patient is middle-aged and presents late in the course of the disease, with a painless slow-growing mass. Clinical manifestations include hoarseness of voice, lower cranial nerve palsies, pulsatile tinnitus, and other neuro-otologic symptoms. The overall prognosis of patients with a cervical paraganglioma is favorable, whereas its temporal bone counterpart often results in recurrence, residual tumor, and neurovascular compromise when in the advanced stage. Pathologic examination reveals a characteristic biphenotypic cell line, composed of chief cells and sustentacular cells with a peripheral fibrovascular stromal layer that are organized into a whorled pattern ("zellballen"). Imaging hallmarks of paragangliomas of the head and neck include an enhancing soft-tissue mass in the carotid space, jugular foramen, or tympanic cavity at computed tomography; a salt-and-pepper appearance at standard spin-echo magnetic resonance imaging; and an intense blush at angiography. Imaging studies depict the location and extent of tumor involvement, help determine the surgical approach, and help predict operative morbidity and mortality. Surgical treatment is definitive. Radiation treatment is included as a palliative adjunct for the exceptional paraganglioma not amenable to surgery.

Clinical and imaging features of cervical chordoma.

OBJECTIVE: We attempted to define the clinical and imaging features of cervical spine chordoma. CONCLUSION: In this series of 10 patients, cervical spine chordomas tended to be large, multilevel destructive lesions of the midcervical region that caused pain and weakness in the neck and shoulder. Typically, these tumors primarily involved the vertebral body and extended into soft tissues of the perivertebral and epidural spaces. Surprisingly, almost a third of the tumors appeared on radiographs to predominantly occupy either the epidural or the intradural space, and nearly half resembled schwannomas. Although no imaging features were pathognomonic, CT and MR imaging were valuable in identifying the tumor, revealing its extent, and defining its relationship to the intraspinal structures.

Mesenchymal chondrosarcoma and simulating lesions of the orbit.

Although an extremely rare neoplasm, orbital mesenchymal chondrosarcoma has a characteristic radiologic appearance. Suspicion of this lesion preoperatively can be of great value to the ophthalmologist because it tends to produce profuse bleeding at biopsy. This article reviews the clinical presentation, pathologic features, and radiologic findings of patients with orbital mesenchymal chondrosarcoma.

Lacrimal gland tumors and simulating lesions. Clinicopathologic and MR imaging features.

The lacrimal gland region can be involved in a wide spectrum of orbital pathology, including inflammatory, lymphoproliferative, and epithelial tumors. This article focuses on benign and malignant epithelial tumors of lacrimal gland and simulating lesions. The clinical presentations, MR imaging, and pathologic findings of lacrimal gland tumors are reviewed.

Congenital cystic masses of the neck: radiologic-pathologic correlation.

Cervical congenital cystic masses constitute an uncommon group of lesions usually diagnosed in infancy and childhood. The most common congenital neck mass is the thyroglossal duct cyst. The diagnosis is easily established from the presence of a cystic lesion in the anterior midline portion of the neck. The vast majority of branchial cleft cysts arise from the second branchial cleft. They can occur anywhere from the oropharyngeal tonsillar fossa to the supraclavicular region of the neck. Cystic hygroma is the most common form of lymphangioma. In the neck, cystic hygromas are most commonly found in the posterior cervical space. They typically extend into adjacent structures without respecting the fascial planes. Dermoid and epidermoid cysts result from sequestration of ectodermal tissue. The floor of the mouth is the most common location in the neck. Cervical thymic cysts are very uncommon lesions and are found anywhere from the angle of the mandible down to the sternum. Laryngoceles are classified into internal, external, and mixed types and have a frequent association with laryngeal carcinoma.

Orbital masses.

The "space approach" will be introduced as a means of analyzing orbital masses on imaging studies. Determination in which space an orbital mass resides, the character of its margin, the presence or absence of bony changes, and evidence of extension of the mass beyond the orbit often allows the radiologist to narrow the differential diagnosis and provides essential information to the ophthalmologist for definitive diagnosis and treatment planning.

Primary central nervous system lymphoma: radiologic-pathologic correlation.

Once an extremely rare neoplasm, primary lymphoma of the central nervous system (CNS) now ranks behind only meningiomas and low-grade astrocytomas in prevalence. Understanding of primary CNS lymphoma has increased greatly in recent years as a result of special immunohistochemical stains. Virtually all primary CNS lymphomas are composed of B cells. Although a viral cause has been suggested in some cases, the exact cause of the disease is still under investigation. Primary CNS lymphoma has a distinct affinity for perivascular extension. Although granular nodules may be seen at gross pathologic inspection, diffuse microscopic spread is always present, which accounts for the ability of this tumor to produce distant disease and local recurrences. The dense cellularity of the tumor and its predilection for the periventricular region also explains its typical hyperattenuated appearance on unenhanced computed tomographic scans and hypointensity on T2-weighted magnetic resonance images. Virtually all lesions enhance with contrast material. Although the overall prognosis for patients with primary CNS lymphoma remains poor, some advances have been made with radiation therapy and chemotherapy for this once uniformly fatal disease.

Neuroimaging--autopsy correlations in AIDS.

This article is a brief review of the radiologic-pathologic correlation of central nervous lesions occurring in patients with AIDS. The major discussions of the imaging appearance and radiologic differential diagnosis have been presented elsewhere in this issue. Our emphasis is on the gross pathologic correlations that are only possible with autopsy materials. We will illustrate the opportunistic neoplasms such as primary CNS lymphoma. This article also discusses the imaging and pathology of the common opportunistic infections. Toxoplasmosis, an obligate intracellular protozoan, is the most common CNS infection producing a mass lesion in AIDS. However, AIDS encephalitis, a direct infection of the brain by the HIV-1 virus itself, may actually be more prevalent. Other viral infections occurring in AIDS include progressive multifocal leukoencephalopathy. Fungal diseases infecting the central nervous system of AIDS patients include cryptococcus, aspergillosis, and mucormycosis. The primary purpose of this article is to demonstrate how the gross pathology correlates with the radiologic images.

MR imaging of the lumbar spine: enhancement of the radicular veins.

Enhancement of lumbar nerve roots in the setting of degenerative disk disease has been considered by several authors as evidence of a breakdown in the blood-nerve barrier induced by nerve root compression [1-3]. Unfortunately, correlation between radicular enhancement and the clinically determined level of radiculopathy has not been consistently shown [4, 5]. We recently proposed that this phenomenon represents intravascular enhancement of radicular veins that travel adjacent to or within the endoneurium of one or more nerve roots of the cauda equina [4, 5]. Our purpose in this pictorial essay is to illustrate the appearance of radicular vein enhancement so that this phenomenon will not be misinterpreted as being clinically significant in the setting of degenerative disk disease.

Contrast-enhanced radicular veins on MR of the lumbar spine in an asymptomatic study group.

PURPOSE: To determine whether radicular enhancement occurs in asymptomatic persons and, if so, to provide insight into the mechanism of such enhancement. METHODS: Thirty asymptomatic volunteers were studied with gadolinium-enhanced MR (0.1 mmol/kg) of the lumbar spine. The precontrast axial T1-weighted sequences were reviewed for the entry section phenomenon of flow-related enhancement. If present, the sequence was repeated in combination with a superior saturation pulse in an attempt to eliminate this phenomenon. All studies were reviewed to document the incidence of radicular enhancement and determine its association with the entry section phenomenon. RESULTS: The entry section phenomenon was observed in 16 of 30 volunteers with successful elimination obtained in all cases. Eighteen of the volunteers demonstrated radicular enhancement; 16 of the 18 enhancing roots were associated with the entry section phenomenon. CONCLUSIONS: Radicular enhancement occurs commonly in asymptomatic volunteers. This phenomenon most likely represents the enhancement of prominent radicular veins. We urge caution in interpreting this finding as abnormal in the symptomatic population with degenerative disk disease.

Enhanced lumbar nerve roots in the spine without prior surgery: radiculitis or radicular veins?

PURPOSE: To evaluate the clinical significance of continuous intradural lumbosacral nerve root enhancement in symptomatic patients without prior lumbar surgery. METHODS: Fifty-three patients without prior back surgery, referred to our institution for evaluation of low-back pain and radiculopathy, were studied with gadolinium-enhanced MR (0.1 mmol/kg) of the lumbar spine. Scans were reviewed for the presence of lumbosacral nerve root enhancement and any associated nerve root compression. Results were correlated with clinical history and physical examinations. RESULTS: Seventeen continuously enhancing nerve roots and two enhancing fila terminale were observed in 13 patients. Eight of 17 (47%) had no referable symptoms. Nine of these nerve roots (53%) were not associated with any degree of nerve root compression. Seven cases (41%) were noted to have flow-related enhancement on the entry section of the T1-weighted axial sequence. CONCLUSIONS: Lumbosacral nerve root enhancement correlates poorly with clinical radiculopathy. The use of contrast enhancement to detect lumbosacral nerve root enhancement in cases in which the unenhanced scan is less than diagnostic is not warranted. The high association between lumbosacral nerve root enhancement and entry-section flow-related enhancement suggests that these enhancing structures within the cauda equina are vessels. It is likely that lumbosacral nerve root enhancement represents intravascular enhancement of radicular veins and not a breakdown in the blood-nerve barrier.

Dysembryoplastic neuroepithelial tumors: MR appearance.

PURPOSE: Dysembryoplastic neuroepithelial tumor (DNT) is a newly described, pathologically benign tumor arising within the supratentorial cortex and having a 100% association with partial complex seizures. We reviewed the MR appearance of the brains of six patients with DNT, without and with administration of gadolinium-DTPA, emphasizing the clinical and radiologic features. METHODS: The MR images in six patients (five male, one female) with pathologically proved DNT were reviewed. Five had partial complex seizures and one had partial simple seizures. Age at onset of partial seizures ranged from 2 to 19 years. Scans were obtained with conventional T1 and T2 weighting without and with the administration of gadolinium-DTPA. All patients had craniotomies for medically refractory seizures and pathologic examination of all specimens was available for review. RESULTS: MR demonstrated a focal cortical mass in all patients. Five were located in the temporal lobe and one was located within the occipital lobe. Two showed enhancement with gadolinium-DTPA. Calcification occurred in one lesion. Common features included very low signal intensity on T1-weighted images and high signal on T2-weighted images, similar to cerebrospinal fluid. Proton density images demonstrated slightly higher signal intensity in the lesion than cerebrospinal fluid. The margin of the tumor is well-circumscribed and may remodel the adjacent calvarium. CONCLUSIONS: DNT, a newly described pathologic entity resulting in chronic, often medically, intractable seizures, has characteristic features on MR that allow it to be suggested in the differential diagnosis. These lesions may simulate benign cysts; however, increased signal intensity on proton density images should prompt further investigation in the proper clinical setting. Differentiation from low-grade astrocytomas and ganglioglioma is not possible by MR.

Multiple aneurysms of the anterior communicating artery.

Multiple aneurysms of the anterior communicating artery are rare. The authors describe a patient who was admitted with a sudden, severe headache with radiation to the neck. Angiograms demonstrated filling of both anterior cerebral arteries and bilateral aneurysms arising from the origin of the anterior communicating artery. Both aneurysms were surgically verified and clipped.