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A L Rhoton

Publications and source records attributed to A L Rhoton.

At least 19 recordsLinked to original sources
PubMed1992

Modified supraorbital craniotomy: technical note.

The authors present a surgical approach that incorporates the frontal sinus and extends a supraorbital craniotomy to include the lateral orbital rim and zygoma. The craniotomy provides wide exposure of the anterior fossa, orbit, ipsilateral middle fossa, and cavernous sinus. The procedure can be performed easily, and the bone flaps can be secured rapidly back into the anatomical position at the time of closure. This modified supraorbital craniotomy is ideal for large benign lesions originating along the sphenoid wing or orbit that expand into the anterior fossa.

Craniotomy↗
PubMed1992

[Microsurgical anatomy of the region near the porus acusticus internus; arteries around the facial and acoustic nerves bundle].

The microsurgical anatomy of the cerebellopontine cistern around the porus acusticus was studied under the surgical microscope, using the heads of 20 cadavers. The relationships among the porus acusticus, facial and acoustic nerves, and neighboring arteries were noted carefully. The arteries were the meatal loop of the cerebellar artery, the internal auditory artery (I.A.A.), the subarcuate artery (S.A.), and the perforating artery (P. A.). The cerebellar arteries made the meatal loop and the arterial-nerve complex while they passed in front of the porus acusticus. Most of the cerebellar arteries were the main or rostral trunk of the AICA. The I.A.A. supplying the facial and acoustic nerves usually originated from the meatal segment of the cerebellar artery and ran into the anterior part of the porus acusticus to enter the internal auditory canal. The S. A. penetrating the subarcuate fossa made a common trunk with I. A. A. or branched from the cerebellosubarcuate artery. One recurrent P. A., a special type of the P. A., was usually present on each side. Since the artery ran between the nerve bundles of the facial and acoustic nerves, it could not be seen through the lateral suboccipital approach.

Arteries↗
PubMed1992

Microsurgical anatomy of acoustic neuroma.

Because acoustic neuromas most frequently arise in the posteriorly placed vestibular nerves, they usually displace the facial and cochlear nerves anteriorly (Figs. 11, 12, and 13). The facial nerve is stretched around the anterior half of the tumor capsule. Variability in the direction of growth of the tumor arising from the vestibular nerves may result in the facial nerve being displaced, not only directly anteriorly, but also anterior-superiorly or anterior-inferiorly. The nerve is infrequently found on the posterior surface of the tumor. Because the facial nerve always enters the facial canal at the anterior-superior quadrant of the lateral margin of the meatus, it is usually easiest to locate it here, rather than at a more medial location where the degree of displacement of the nerve is more variable. The cochlear nerve also lies anterior to the vestibular nerve and is most frequently stretched around the anterior half of the tumor. The strokes of the fine dissecting instruments used in removing the tumor should be directed along the vestibulocochlear nerve from medial to lateral rather than from lateral to medial because traction medially may tear the tiny filaments of the cochlear nerve at the site where these filaments penetrate the lateral end of the meatus to enter the cochlea. The landmarks that are helpful in identifying the facial and vestibulocochlear nerves at the brain stem on the medial side of the tumor have been reviewed. These nerves, although distorted by tumor, can usually be identified on the brain stem side of the tumor at the lateral end of the pontomedullary sulcus, just rostral to the glossopharyngeal nerve and just anterior-superior to the foramen of Luschka, flocculus, and choroid plexus protruding from the foramen of Luschka. After the facial and vestibulocochlear nerves are identified on the medial and lateral sides of the tumor, the final remnants of the tumor are separated from the intervening segment of the nerves. In the three approaches to the meatus and cerebellopontine angle--retrosigmoid, translabyrinthine, and middle fossa--a communication may be established between the subarachnoid space and the mastoid air cells that requires careful closure to prevent a cerebrospinal fluid leak.

Brain Stem↗
PubMed1991

Long-term follow-up of radiotherapy for pituitary adenoma: the absence of late recurrence after greater than or equal to 4500 cGy.

Recent literature has suggested that late recurrence of pituitary adenoma after radiotherapy is common. We hypothesized that late failures might be a result of inadequate dose (less than 4500 cGy). To investigate, we analyzed 105 patients treated at our institution between 1965 and 1986 (analysis, 2/89). The minimum observation time was greater than or equal to 5 years in 58% and greater than or equal to 10 years in 30% of the patients. All patients received megavoltage radiotherapy (range, 4200-5500 cGy; mean, 4821 cGy) at a mean dose per fraction of 172 cGy; 100 patients received greater than or equal to 4500 cGy tumor dose. Twenty-nine patients received radiotherapy alone, and 76 had postoperative radiotherapy after frontal craniotomy (20 patients) or transsphenoidal hypophysectomy (56 patients). At presentation, 71% of patients had extrasellar disease, 57% had visual field deficits, and 50% had endocrinopathy. Of patients treated postoperatively, 74% had gross residual disease. Four local failures occurred at 13, 16, 57, and 64 months after postoperative radiotherapy, all within the irradiated volume (tumor doses of 4700, 4715, 5000, and 5100 cGy). All four patients had presented with moderate to extensive extrasellar disease with visual field defects. Two of the four remain free of second recurrence at 7 and 13 years after salvage transsphenoidal hypophysectomy. The local control rate with radiotherapy (product-limit method) at 10 years was 100% in the radiotherapy-alone group and 92% in the postoperative radiotherapy group (95% for all patients). To prevent bias, seven patients who received bromocriptine, none of whom demonstrated a recurrence, were censored from the local control analysis at the initiation of the drug. No patient in this study suffered recurrence greater than 64 months after radiotherapy, with 31 patients (none with bromocriptine) observed 10 to 21 years. We conclude that treatment of pituitary adenoma with greater than or equal to 4500 cGy in 25 fractions can result in a high (greater than or equal to 90%) probability of stable long-term control.

Adenoma↗
PubMed1991

Radiation-induced optic neuropathy: a magnetic resonance imaging study.

Optic neuropathy induced by radiation is an infrequent cause of delayed visual loss that may at times be difficult to differentiate from compression of the visual pathways by recurrent neoplasm. The authors describe six patients with this disorder who experienced loss of vision 6 to 36 months after neurological surgery and radiation therapy. Of the six patients in the series, two had a pituitary adenoma and one each had a metastatic melanoma, multiple myeloma, craniopharyngioma, and lymphoepithelioma. Visual acuity in the affected eyes ranged from 20/25 to no light perception. Magnetic resonance (MR) imaging showed sellar and parasellar recurrence of both pituitary adenomas, but the intrinsic lesions of the optic nerves and optic chiasm induced by radiation were enhanced after gadolinium-diethylenetriaminepenta-acetic acid (DTPA) administration and were clearly distinguishable from the suprasellar compression of tumor. Repeated MR imaging showed spontaneous resolution of gadolinium-DTPA enhancement of the optic nerve in a patient who was initially suspected of harboring recurrence of a metastatic malignant melanoma as the cause of visual loss. The authors found the presumptive diagnosis of radiation-induced optic neuropathy facilitated by MR imaging with gadolinium-DTPA. This neuro-imaging procedure may help avert exploratory surgery in some patients with recurrent neoplasm in whom the etiology of visual loss is uncertain.

Aged↗
PubMed1991

Chiari malformation with syringocephaly. Case report.

A 69-year-old white woman presented with a left hemiparesis which progressed to quadriparesis and encephalopathy. Computerized tomography and magnetic resonance imaging revealed a Chiari I malformation and a hydromyelic cavity extending from C-2 to T-6. Rostrally, the cavity extended through the ventral medulla, pons, and right cerebral peduncle into the right cerebral hemisphere, where the cavity enlarged and was associated with mass effect. The patient has made a dramatic neurological recovery following suboccipital craniectomy with insertion of a dural graft to decompress the Chiari malformation and upper cervical laminectomy and dorsal root entry zone myelotomy to decompress the hydromyelia.

Aged↗
PubMed1990

Surgical approaches to the cavernous sinus: a microsurgical study.

The surgical approaches to the cavernous sinus were examined in 50 adult cadaveric cavernous sinuses using magnification of X3 to X40. The following approaches were examined: 1) the superior intradural approach directed through a frontotemporal craniotomy and the roof of the cavernous sinus; 2) the superior intradural approach combined with an extradural approach for removing the anterior clinoid process and unroofing the optic canal and orbit; 3) the superomedial approach directed through a supraorbital craniotomy and subfrontal exposure to the wall of the sinus adjacent to the pituitary gland; 4) the lateral intradural approach directed below the temporal lobe to the lateral wall of the sinus; 5) the lateral extradural approach for exposure of the internal carotid artery in the floor of the middle cranial fossa proximal to the sinus; 6) the combined lateral and inferolateral approach, in which the infratemporal fossa was opened and the full course of the petrous carotid artery and the lateral wall of the sinus were exposed and; 7) the inferomedial approach, in which the medial wall of the sinus was exposed by the transnasal-transsphenoidal route. It was clear that a single approach was not capable of providing access to all parts of the sinus. The intracavernous structures best exposed by each route are reviewed. The osseous relationships in the region were examined in dry skulls. Anatomic variants important in exposing the cavernous sinus are reviewed.

Adult↗
PubMed1990

Neurosurgery in the decade of the brain. The 1990 AANS presidential address.

The decade of the 1990's has provided neurosurgery with multiple challenges and opportunities. Numerous developments hold a promise for making the 1990's the most rewarding decade of the 20th century for neurosurgery. The "Decade of the Brain" resolution, adopted by the United States House and Senate and signed into law by President Bush in 1989, has provided the specialty with staggering opportunities. Neurosurgery and the basic and clinical neurosciences would be strengthened by the development of a major new philanthropic organization called the "American Brain Association" that would carry the activities of the Decade of the Brain into the 21st century. Major efforts are being made to improve organized neurosurgery's responsiveness to member needs. These include the strategic planning project undertaken by the Board of Directors of the American Association of Neurological Surgeons (AANS) and efforts to strengthen the Joint Council of State Neurosurgical Societies. The AANS has been extremely active in representing the specialty in legislative matters in Washington and in multiple other forums. This Association has joined The American Board of Neurological Surgery and the Residency Review Committee in responding to orthopedic surgery's proposal for spine fellowships. It is proposed that the logo of the state, regional, and national neurosurgical societies be changed to depict our involvement in spinal surgery (as well as brain surgery) because spinal surgery represents more than half of the total effort of this specialty. The standards of worth and value that provide the driving force behind our work emphasize the need to grow in compassion as manifested by our kindness, sincerity, and concern as we grow in professional competence as reflected by our training, knowledge, and skill.

Brain↗
PubMed1989

The microsurgical anatomy of the infratentorial lateral supracerebellar approach to the trigeminal nerve for tic douloureux.

The increasing use of microsurgical decompression for trigeminal neuralgia has created a need for more detailed anatomical information about the approach. To define better this anatomy, 10 cerebellar specimens obtained at autopsy were examined, and intraoperative findings in 30 patients with trigeminal neuralgia were analyzed. Since the infratentorial subdural space on the tentorial cerebellar surface is exposed to explore the trigeminal nerve in the infratentorial lateral supracerebellar approach, attention was directed to the following: the anterolateral margin of the cerebellar hemisphere, bridging veins on the tentorial surface, superior petrosal veins, and relationships between blood vessels and the trigeminal nerve. The lateral mesencephalic segment of the superior cerebellar artery at or near the bifurcation often compressed the nerve laterally at more than one point. With this approach, the relationship of the superior cerebellar artery to the nerve could be observed from the medial side of the tentorial surface. The infratentorial lateral supracerebellar approach is discussed and compared to Dandy's cerebellar route.

Arteries↗
PubMed1989

Microsurgical anatomy of the tentorial sinuses.

Variations of the tentorial sinus of cadaver cerebellar tentoria were examined under a surgical microscope. The tentorial sinuses were classified into four groups: Group I, in which the sinus received venous blood from the cerebral hemisphere; Group II, in which the sinus drains the cerebellum; Groups III, in which the sinus originates in the tentorium itself; and Group IV, in which the sinus originates from a vein bridging to the tentorial free edge. The tentorial sinuses of Groups I and II were frequently located in the posterior portion of the tentorium. The sinuses of Group I were short and most frequently present in the lateral portion of the tentorium. The tentorial sinuses of Group II, which were usually large and drained into the dural sinuses near the torcular, were separated into five subtypes according to the draining veins and direction of termination. The tentorial sinuses of Groups III and IV were located near the tentorial free edge or the straight sinus. The draining patterns of the tentorial sinuses and their draining veins (so-called "bridging veins") were present in most cases. Knowledge of this anatomy can benefit the neurosurgeon carrying out repair near or on the cerebellar tentorium.

Cerebellum↗
PubMed1988

Microsurgical anatomy of the choroidal fissure.

The microsurgical anatomy of the choroidal fissure was examined in 25 cadaveric heads. The choroidal fissure, the site of attachment of the choroid plexus in the lateral ventricle, is located between the fornix and thalamus in the medial part of the lateral ventricle. The choroidal fissure is divided into three parts: (a) a body portion situated in the body of the lateral ventricle between the body of the fornix and the thalamus, (b) an atrial part located in the atrium of the lateral ventricle between the crus of the fornix and the pulvinar, and (c) a temporal part situated in the temporal horn between the fimbria of the fornix and the lower surface of the thalamus. The three parts of the fissure are the thinnest sites in the wall of the lateral ventricle bordering the basal cisterns and the roof of the third ventricle. Opening through the body portion of the choroidal fissure from the lateral ventricle exposes the velum interpositum and third ventricle. Opening through the temporal portion of the choroidal fissure from the temporal horn exposes the structures in the ambient and crural cisterns. Opening through the atrial portion of the fissure from the atrium exposes the quadrigeminal cistern, the pineal region, and the posterior portion of the ambient cistern. The neural, arterial, and venous relationships of each part of the fissure are reviewed. The operative approaches directed through each part of the fissure are also reviewed.

Cerebral Arteries↗
PubMed1988

Microsurgical anatomy of the posterior fossa cisterns.

The microsurgical anatomy of the posterior fossa cisterns was examined in 15 cadavers using 3X to 40X magnification. Liliequist's membrane was found to split into two arachnoidal sheets as it spreads upward from the dorsum sellae: an upper sheet, called the diencephalic membrane, which attaches to the diencephalon at the posterior edge of the mamillary bodies, and a lower sheet, called the mesencephalic membrane, which attaches along the junction of the midbrain and pons. Several other arachnoidal membranes that separate the cisterns were identified. These include the anterior pontine membrane, which separates the prepontine and cerebellopontine cisterns; the lateral pontomesencephalic membrane, which separates the ambient and cerebellopontine cisterns; the medial pontomedullary membrane, which separates the premedullary and prepontine cisterns; and the lateral pontomedullary membrane, which separates the cerebellopontine and cerebellomedullary cisterns. The three cisterns in which the arachnoid trabeculae and membranes are the most dense and present the greatest obstacle at operation are the interpeduncular and quadrigeminal cisterns and the cisterna magna. Numerous arachnoid membranes were found to intersect the oculomotor nerves. The neural and vascular structures in each cistern are reviewed.

Brain↗
PubMed1986

Microsurgical anatomy of the brainstem surface facing an acoustic neuroma.

There is a consistent set of relationships on the brainstem surface facing an acoustic neuroma that provides the basis for identifying the displaced facial nerve on the medial side of the tumor. This review of the microsurgical anatomy of the brainstem surface facing an acoustic neuroma is based on the examination of the side of the brainstem during 42 operations for the removal of acoustic neuroma, and on the study of 50 cadaveric brains in the microsurgery laboratory. In the operative series, which included many large tumors, the facial nerve was preserved at operation in over 90% of the 42 patients. There was no mortality, and no need for cerebellar resection to remove the tumor in any patient.

Arteries↗
PubMed1986

Primary leptomeningeal glioma mimicking an acoustic neuroma: case report with review of the literature.

Primary leptomeningeal gliomas are rare. Historically, they have been found in the spinal canal more frequently; however, in the recent literature nearly all have been found within the cranium. In the only cadaveric study of leptomeningeal glial nests, the most frequent site was the medulla and pons. Until now, no leptomeningeal glioma has been found at this site. We report what we believe to be the first such case mimicking an acoustic neuroma.

Adolescent↗
PubMed1986

Microsurgical anatomy and operative approaches to the lateral ventricles.

The anatomy needed to plan microoperative approaches to the lateral ventricles was examined in 20 cadaveric cerebral hemispheres. The neural, arterial, and venous structures in the walls of the lateral ventricles and the relationship of the lateral ventricles to the third ventricle and basal cisterns were examined. The operative approaches to the lateral ventricle are reviewed.

Arteries↗
PubMed1985

Microsurgical anatomy of the region of the foramen magnum.

The anatomy needed to plan microoperative approaches to the region of the foramen magnum was examined in 25 cadaveric heads. The structures examined included the lower cranial and upper spinal nerves, the caudal brain stem and rostral spinal cord, the vertebral artery and its branches, the veins and dural sinuses at the craniovertebral junction, and the ligaments and muscles uniting the atlas, axis, and occipital bone. The transoral, transpalatal, labiomandibular, glossolabiomandibular, transsphenoidal, transcranial-transbasal, transcervical, and suboccipital operative approaches to the region are also reviewed.

Atlanto-Occipital Joint↗