Basiparallel Extraaxial
Tomography Mass in the
to Diagnosis of an Posterior Fossa
Satoru WATANABE*, Keiji NAKAJIMA, Hirotoshi SUMIE and Yutaka KURU**. *Departmentof Neurosurgery, Juntendo UniversitySchool of Medicine, Hongo 2-1-1, Bunkyo-Ku,Tokyo, Japan. **Departmentof Radiology, Juntendo UniversitySchool of Medicine, Hongo 2-1-1, Bunkyo-Ku,Tokyo, Japan. Summary The basiparallel cut, which is a tomography parallel to the base of the posterior fossa, gives some additive value to the diagnosis of an extraaxial mass by pneumoencephalo graphy. The view is considerably similar to the operation view through the suboccipital approach. The anteroposterior extension and involvement of the jugular foramen by an acoustic neurinoma are clearly demonstrated by this view. Also, consistency of a mass can be estimated to a certain degree. key words: pneumoencephalography,tomography, posterior fossa, extraaxial tumor, acoustic neurinoma Introduction By pneumoencephalotomography of the pos terior fossa its contents are demonstrated as a slice in various planes. The lateral and frontal tomography were ordinarily made,"" while another horizontal or deep frontal cutting 1.2.3.6.7) was not frequently applied to the exam ination.
A specimen
of the cerebellum
sliced
parallel to the brain stem axis was called "Basi parallelschnitt" by an anatomist, Ziehen91. We prefer to call such a horizontal tomogram of the posterior fossa "basiparallel cut." This cut en ables visualization of structures in the planes parallel to the base of the posterior fossa, clivus, and makes it possible to analyze small changes on the walls of the fourth ventricle as well as in the cisterns lateral to the brain stem6.7). Eleven cases of acoustic neurinoma, one of a clival chordoma and one of a cerebellopontine angle meningioma have been examined by this technique. Of these cases, three acoustic neu rinomas and one clival chordoma are illustrated and analyzed in this report. Examination
Technique
Basiparallel tomography was made following the other two projections, the frontal and lateral,
for which procedure the patient was kept in a sitting position. For the third tomography the patient was laid prone on the table tilted 15 degrees head-side up. We made the basiparallel cuts always keeping the patient's head brow-up so as to place the clivus possibly parallel to the film. The air introduced into the fourth ventricle and the subarachnoid space remains in the pos terior fossa as long as the patient stays in a prone position. Such a position will certainly reduce irritation to the subarachnoid membrane. The patients did not complain of headache after such examinations as long as they were kept prone in bed. The air then flows into the spinal sub arachnoid space to be absorbed there from. Four to five basiparallel cuts are sufficient to observe any changes on the fourth ventricle walls and in the cisterns lateral to the brain stem. Case 1. A 49-year-old man. A left cerebel lopontine angle tumor was found on the frontal cuts at the middle and lower pons levels (Fig. la). The anteroposterior extension of this tumor was most clearly demonstrated on the basiparallel cut film (Fig. lb). On the right, normal side, the lateral part of the ambient cistern and the lateral pontine cistern were well defined with air. On the left side the whole lateral pontine cistern was obliterated. A small portion of the air remained at the inlet of the jugular foramen. The bony
a)
A frontal cut at the middle pons level. Only the medial outline of the mass can be seen (arrows). Deformity of the fourth ventricle is not evident.
Fig.
1
Case
1. An acoustic
neurinoma
cortex of the foramen, as compared with the opposite one, appeared uneven, if not de structed. The specimen taken at the operation shows a large proportion of tissue identified as
a)
A frontal cut at the upper pons level. The outline of the mass is clearly depicted with air (arrows).
Fig. 2
Case
2. An acoustic
b) A basiparallel cut shows the anteroposterior extension of this mass (arrows). On the normal side the lateral portion of the ambient cistern and the lateral pontine cistern are well out lined, while these cisterns are obliterated on the left.
neurinoma
of Antoni
Antoni
B-type
on the left
B-type.
Case 2. A 60-year-old man. On the frontal cut at the upper pons level, a rugged outline of a tumor appeared at the left of the pons (Fig. 2a).
b) The dorsal portion left lateral pontine some slack around the left wall of the of Antoni
A-type
of the mass extends into the cistern (arrows) and makes itself. Note the deformity on fourth ventricle (IV).
on the left side
The basiparallel cut at the fourth ventricle floor revealed considerable asymmetry of the lateral wall. The left wall of the ventricle was deformed and appeared likely to be elevated (Fig. 2b). With this deformity of the ventricle and the appearance of a slack in the left ambient cistern, the tumor was thought to be solid and rugged on the outline. Histological study of the specimen revealed that the major portion of the neurinoma con sisted of tissue of Antoni A-type. Case 3. A 60-year-old woman. An acoustic neurinoma on the left side. The anteroposterior extension of the tumor appeared evident on the basiparallel cut at the brain stem level (Fig. 3). There was an increased slack at the left of the mid-brain. Somewhat rugged outline of the mass was clearly demonstrated. Its lateral portion extended not only into the internal auditory meatus, but also into the jugular foramen. The brain stem was slightly bent at the junction between the pons and the medulla oblongata. By operation, the tumor was found to be solid and elastic. The specimen of the tumor showed An tom A-type in the greater part of the tissue. Case 4. A 65-year-old man. A large clival chordoma was naturally extraaxial and lay on the midline. A solid and rugged mass extended to the skull base from the supratentorial to the infratentorial space and it lifted up the brain stem from below. The interpeduncular cistern and prepontine cistern were rather increased in
a)
A frontal cut at the mid-brain level shows the dorsal surface of the mass (arrows). Enlarge ment of the peduncular cistern is obvious.
Fig. 4
Case
Fig. 3 Case 3. An acoustic A-type. A basiparallel cut stem. The rugged outline defined with air pooling rows). A portion of the jugular
b)
4. A clival
neurinoma of Antom at the axis of the brain of the mass is sharply in enlarged cisterns (ar mass extends into the
foramen (J).
A basiparallel cut at the fourth ventricle floor. The fourth ventricle (IV) and the lower brain stem (arrows) appear on this cut. The ventricle is flattened by the mass lying on the clivus. chordoma
capacity (Fig. 4a). But there was no visible slack on either side of the brain stem. The fourth ventricle was elevated and flattened symmetri cally (Fig. 4b). Discussion Extraaxial mass growing at either side of the brain stem was to be depicted with air, regard less of a projection or of a tomographic plane selected. The frontal and lateral tomographies sufficiently demonstrated an outline of a cerebel lopontine angle tumor' 3,4,5,7,8).The basiparal lel cut, however, was thought to have additive value in the diagnosis3'8~.This cutting is capable of providing a view considerably similar to that as seen through the suboccipital approach in operation. The anteroposterior extension of such tumors are obvious on a single film of this cutting. Also extension of a tumor into the jugular foramen or involvement of the lower cranial nerves can be proved by this tomo graphy. When an extraaxial mass is relatively solid and it has a rugged surface, a considerable slack between the normal structures and the tumor appears. It is the sign for most cerebellopontine angle tumors. When a tumor is quite soft and does not create so much slack around itself, there may be no room to pool sufficient air to contour the mass. In such a tumor, pneumoen cephalotomography is incapable of compassing the whole outline of a mass. A basiparallel cut at the fourth ventricle floor level may give a sug
gestion to estimate consistency owing to the degree of deformity
of a tumor, of the floor.
References 1) Bories, J., Fredy, F. and Rosier, J.: Etude tomoen cephalographique des atrophies cerebelleuses. Acta radio!. 13: 353-369, 1972 2) Corrales, M. and Greitz, T.: Fourth ventricle. I. A morphologic and radiologic investigation of the normal anatomy. Acta radio!. 12: 113-133, 1972 3) Corrales, M.: Fourth ventricle. III. Intra-and extraaxial tumours. Acta radiol. 13: 370-390, 1972 4) Di Chiro, G.: An atlas of pathologic pneumoen cephalographic anatomy. Charles C. Thomas, Springfield, Illinois, 1967 5) Iwabuchi, T. and Suzuki, J.: Diagnosis of acoustic neurinoma by pneumoencephalo-roulette to mography. J. Neurosurg. 29: 307-311, 1968 6) Kuru, Y.: Roentgen anatomy of the cerebellum. Shinkeishinpo. 19: 618-626, 1975 (Japanese) 7) Pertuiset, B.: Les neurinomes de l' acoustique. Developpes dans 1' angle pontocerebelleux. Neurochirurgie 16: Supplement 1, 1970 8) Tanaka, T., Kowada, M., Miura, G. and Iwa buchi, T.: An application of pneumoencephalo roulette tomography to the diagnosis of sub occipital lesions: Especially combined with pneumoventriculography. Brain and Nerve. 21: 1353-1359, 1969 9) Ziehen, Th.: Bardeleben's Handbuch der Anat omie des Menschen, Nervensystem. Bd. 4. Abt. 1. Gustav Fischer Verlag, Jena, 1934
Tomography Mass in the
to Diagnosis of an Posterior Fossa
Satoru WATANABE*, Keiji NAKAJIMA, Hirotoshi SUMIE and Yutaka KURU**. *Departmentof Neurosurgery, Juntendo UniversitySchool of Medicine, Hongo 2-1-1, Bunkyo-Ku,Tokyo, Japan. **Departmentof Radiology, Juntendo UniversitySchool of Medicine, Hongo 2-1-1, Bunkyo-Ku,Tokyo, Japan. Summary The basiparallel cut, which is a tomography parallel to the base of the posterior fossa, gives some additive value to the diagnosis of an extraaxial mass by pneumoencephalo graphy. The view is considerably similar to the operation view through the suboccipital approach. The anteroposterior extension and involvement of the jugular foramen by an acoustic neurinoma are clearly demonstrated by this view. Also, consistency of a mass can be estimated to a certain degree. key words: pneumoencephalography,tomography, posterior fossa, extraaxial tumor, acoustic neurinoma Introduction By pneumoencephalotomography of the pos terior fossa its contents are demonstrated as a slice in various planes. The lateral and frontal tomography were ordinarily made,"" while another horizontal or deep frontal cutting 1.2.3.6.7) was not frequently applied to the exam ination.
A specimen
of the cerebellum
sliced
parallel to the brain stem axis was called "Basi parallelschnitt" by an anatomist, Ziehen91. We prefer to call such a horizontal tomogram of the posterior fossa "basiparallel cut." This cut en ables visualization of structures in the planes parallel to the base of the posterior fossa, clivus, and makes it possible to analyze small changes on the walls of the fourth ventricle as well as in the cisterns lateral to the brain stem6.7). Eleven cases of acoustic neurinoma, one of a clival chordoma and one of a cerebellopontine angle meningioma have been examined by this technique. Of these cases, three acoustic neu rinomas and one clival chordoma are illustrated and analyzed in this report. Examination
Technique
Basiparallel tomography was made following the other two projections, the frontal and lateral,
for which procedure the patient was kept in a sitting position. For the third tomography the patient was laid prone on the table tilted 15 degrees head-side up. We made the basiparallel cuts always keeping the patient's head brow-up so as to place the clivus possibly parallel to the film. The air introduced into the fourth ventricle and the subarachnoid space remains in the pos terior fossa as long as the patient stays in a prone position. Such a position will certainly reduce irritation to the subarachnoid membrane. The patients did not complain of headache after such examinations as long as they were kept prone in bed. The air then flows into the spinal sub arachnoid space to be absorbed there from. Four to five basiparallel cuts are sufficient to observe any changes on the fourth ventricle walls and in the cisterns lateral to the brain stem. Case 1. A 49-year-old man. A left cerebel lopontine angle tumor was found on the frontal cuts at the middle and lower pons levels (Fig. la). The anteroposterior extension of this tumor was most clearly demonstrated on the basiparallel cut film (Fig. lb). On the right, normal side, the lateral part of the ambient cistern and the lateral pontine cistern were well defined with air. On the left side the whole lateral pontine cistern was obliterated. A small portion of the air remained at the inlet of the jugular foramen. The bony
a)
A frontal cut at the middle pons level. Only the medial outline of the mass can be seen (arrows). Deformity of the fourth ventricle is not evident.
Fig.
1
Case
1. An acoustic
neurinoma
cortex of the foramen, as compared with the opposite one, appeared uneven, if not de structed. The specimen taken at the operation shows a large proportion of tissue identified as
a)
A frontal cut at the upper pons level. The outline of the mass is clearly depicted with air (arrows).
Fig. 2
Case
2. An acoustic
b) A basiparallel cut shows the anteroposterior extension of this mass (arrows). On the normal side the lateral portion of the ambient cistern and the lateral pontine cistern are well out lined, while these cisterns are obliterated on the left.
neurinoma
of Antoni
Antoni
B-type
on the left
B-type.
Case 2. A 60-year-old man. On the frontal cut at the upper pons level, a rugged outline of a tumor appeared at the left of the pons (Fig. 2a).
b) The dorsal portion left lateral pontine some slack around the left wall of the of Antoni
A-type
of the mass extends into the cistern (arrows) and makes itself. Note the deformity on fourth ventricle (IV).
on the left side
The basiparallel cut at the fourth ventricle floor revealed considerable asymmetry of the lateral wall. The left wall of the ventricle was deformed and appeared likely to be elevated (Fig. 2b). With this deformity of the ventricle and the appearance of a slack in the left ambient cistern, the tumor was thought to be solid and rugged on the outline. Histological study of the specimen revealed that the major portion of the neurinoma con sisted of tissue of Antoni A-type. Case 3. A 60-year-old woman. An acoustic neurinoma on the left side. The anteroposterior extension of the tumor appeared evident on the basiparallel cut at the brain stem level (Fig. 3). There was an increased slack at the left of the mid-brain. Somewhat rugged outline of the mass was clearly demonstrated. Its lateral portion extended not only into the internal auditory meatus, but also into the jugular foramen. The brain stem was slightly bent at the junction between the pons and the medulla oblongata. By operation, the tumor was found to be solid and elastic. The specimen of the tumor showed An tom A-type in the greater part of the tissue. Case 4. A 65-year-old man. A large clival chordoma was naturally extraaxial and lay on the midline. A solid and rugged mass extended to the skull base from the supratentorial to the infratentorial space and it lifted up the brain stem from below. The interpeduncular cistern and prepontine cistern were rather increased in
a)
A frontal cut at the mid-brain level shows the dorsal surface of the mass (arrows). Enlarge ment of the peduncular cistern is obvious.
Fig. 4
Case
Fig. 3 Case 3. An acoustic A-type. A basiparallel cut stem. The rugged outline defined with air pooling rows). A portion of the jugular
b)
4. A clival
neurinoma of Antom at the axis of the brain of the mass is sharply in enlarged cisterns (ar mass extends into the
foramen (J).
A basiparallel cut at the fourth ventricle floor. The fourth ventricle (IV) and the lower brain stem (arrows) appear on this cut. The ventricle is flattened by the mass lying on the clivus. chordoma
capacity (Fig. 4a). But there was no visible slack on either side of the brain stem. The fourth ventricle was elevated and flattened symmetri cally (Fig. 4b). Discussion Extraaxial mass growing at either side of the brain stem was to be depicted with air, regard less of a projection or of a tomographic plane selected. The frontal and lateral tomographies sufficiently demonstrated an outline of a cerebel lopontine angle tumor' 3,4,5,7,8).The basiparal lel cut, however, was thought to have additive value in the diagnosis3'8~.This cutting is capable of providing a view considerably similar to that as seen through the suboccipital approach in operation. The anteroposterior extension of such tumors are obvious on a single film of this cutting. Also extension of a tumor into the jugular foramen or involvement of the lower cranial nerves can be proved by this tomo graphy. When an extraaxial mass is relatively solid and it has a rugged surface, a considerable slack between the normal structures and the tumor appears. It is the sign for most cerebellopontine angle tumors. When a tumor is quite soft and does not create so much slack around itself, there may be no room to pool sufficient air to contour the mass. In such a tumor, pneumoen cephalotomography is incapable of compassing the whole outline of a mass. A basiparallel cut at the fourth ventricle floor level may give a sug
gestion to estimate consistency owing to the degree of deformity
of a tumor, of the floor.
References 1) Bories, J., Fredy, F. and Rosier, J.: Etude tomoen cephalographique des atrophies cerebelleuses. Acta radio!. 13: 353-369, 1972 2) Corrales, M. and Greitz, T.: Fourth ventricle. I. A morphologic and radiologic investigation of the normal anatomy. Acta radio!. 12: 113-133, 1972 3) Corrales, M.: Fourth ventricle. III. Intra-and extraaxial tumours. Acta radiol. 13: 370-390, 1972 4) Di Chiro, G.: An atlas of pathologic pneumoen cephalographic anatomy. Charles C. Thomas, Springfield, Illinois, 1967 5) Iwabuchi, T. and Suzuki, J.: Diagnosis of acoustic neurinoma by pneumoencephalo-roulette to mography. J. Neurosurg. 29: 307-311, 1968 6) Kuru, Y.: Roentgen anatomy of the cerebellum. Shinkeishinpo. 19: 618-626, 1975 (Japanese) 7) Pertuiset, B.: Les neurinomes de l' acoustique. Developpes dans 1' angle pontocerebelleux. Neurochirurgie 16: Supplement 1, 1970 8) Tanaka, T., Kowada, M., Miura, G. and Iwa buchi, T.: An application of pneumoencephalo roulette tomography to the diagnosis of sub occipital lesions: Especially combined with pneumoventriculography. Brain and Nerve. 21: 1353-1359, 1969 9) Ziehen, Th.: Bardeleben's Handbuch der Anat omie des Menschen, Nervensystem. Bd. 4. Abt. 1. Gustav Fischer Verlag, Jena, 1934
