Cross Sectional Anatomy

Relevance of Cross Sectional Anatomy in Diagnostic and Therapeutic Measures

“Man’s World has always been grounded upon his body as its center, from it and its necessities he has circled out and learned what he knows about the universe”

Introduction

Clinical anatomy is fascinating – most essential for clinicians. Anatomy is boring – most essential for surgeons. Cross sectional anatomy is informative and amusing – most essential for anatomists, radiologists, sonologists and surgeons.

The understanding of the cross sectional anatomy is basic to the proper interpretation in the various diagnostic procedures like computerized tomography, ultrasound, magnetic resonance imaging, position emission tomography , SPECT, nuclear imaging technic, as it reveals the three dimensional relationships of various structures of the body. The study of anatomy through the use of the cross section has fallen into disuse in western countries during 18th century. In our country it has rarely made its appearance in the curriculum of under graduates and post graduates or in the relevant clinical materials.

The study of anatomy of cross section even though it has begun in the 16th century it could not have its relevance either in diagnostic and therapeutic use till 1911. The ignorance of the importance of cross sectional anatomy to the eastern people may be due to under development of technology and lack of awareness of the newer imaging technics in radiology.

History

History of anatomy started in the early part of the 16th century by chamberlain, Chouland, Andreas Vesalius, Vidius, Bartholin and Graaaf. The further development was not a rapid pace due the lack of methods, which would harden the bodies. Pioneer work by the Russian anatomist and surgeon Nicolas Pirogiff during 1852 to 1858 and Legender using the method of hardening the various parts of the body in alcohol and the method of decalcifying the entire pelvis in by weak nitric acid. In the early part of 19th century De Riemer’s Dutch anatomist revived this method thereby bringing out its importance once again.

The study of cross sectional anatomy entered a new era after the introduction of formalin as a hardening substance in the 1895 by Gerota which was later modified by Terry using a solution made of equal parts 50% formalin without using any freezing techniques.

Preparation of sections and preservation of specimens

1. Selection of Cadaver:
   1. Age: Middle aged individual
   2. Bodily habitus: It should have a well developed muscular system, skeletal system. Organs should be empty at the time of section. Cause of death should not have produced gross anatomical change.

2. Embalming the Cadaver: The so selected cadaver is injected with embalming fluid to retain the colour of the muscle and organs.

3. Circumferential measurements – head, neck, thorax, abdomen and limbs.

4. Marking of the planes on the surface of the body.

The following plane are to be marked and photographs are to be taken.

Supra orbito meatal plane Infra orbito meatal plane – FRANKFORT’S PLANE – Plane of sternal angle Inter spinal plane The cadaver after embalming is kept for freezing for 3 days then kept in a supine position and the following sections are made into 10cms thickness.

In the head and neck region

1. Oblique head sections are made along the supra orbito meatal plane at 20-25 degree to the infra orbito meatal plane. Oblique head sections OH-1 to OH 10 with sections of 1 to 2 cm’s thickness are made for the study of orbit oral cavity, nasal cavity. (Enclosure IA, 2A,3A).

Neuro ocular plane defined as the computerized tomography plane passing through both lenses, optic nerve heads and optic canal in position of gaze – It includes all visual pathways starting from cornea to clacarine fissure. It would reflect orientation of the temporal horn of lateral ventricle , thus enhancing the accuracy of 3 dimensional approach in the evaluation of orbito- cephalic anatomy and diagnosis. In the neck, thorax, abdomen, pelvis, and limbs horizontal sections are made similar to above. (Enclosure II, III, IV, V, VI). After making the sections each section is covered with an x-ray film on both the surfaces and kept in a deep freezer. Then each section is washed carefully to remove the debris and frozen contents from all organs. The thin sections are kept for photographs and analytical study. The sections so made are treated with propylene glycol to prevent reflections and photographs are taken using sophisticated equipment. The specimens can be preserved for a longer duration with a solution known as Jores II fluid (1000ml distilled water, 20 ml glycerol, 100ml potassium acetate). The sections are secured by suturing or with gelatin glue.

Study of the prepared sections and photographs:

The study of human organs or system by radiology and dissection will help us to know the 2 dimensional picture of the structure whereas cross sectional approach to anatomy provides a synthesis of putting together the knowledge gain by dissection into easily understandable three dimensional picture.

The three dimensional sense can be obtained by studying serial sections following a given single system or single structure, following back and forth and also following the series of sections for a study of another structure of system present in the series and noting their inter relations. Similar study of all the structures of all the system in a given series of adjacent sections can be interpreted and final outlook of a given cross section, given structure of system can be obtained.

After having obtained a sense of 3 dimensional picture using cross sectional anatomy , the same knowledge can be made use to study the pictures obtained by the newer radiological techniques for diagnostic purpose by CT, PET, MRI.

Basic principles in the study of cross sectional anatomy:

Study of cross sectional anatomy of any section may not reveal the complete 3 dimensional relations of any organs of system, hence a series of adjacent sections have to be studied to get the dimensional picture. Eg; The horizontal sections of the neck of 1 or 2 cm’s thickness at the level of C5 may fail to reveal the presence of the parathyroid gland which measures hardly 5 to 6mm in length.

Correlation between cross sectional anatomy and newer imaging techniques;

1. The size and shape of an object can vary in different sections (oblique and horizontal ) and in different scans.
2. The successive sections taken close together will never appear same.
3. Scans with contrast medium will be showing extremely denser areas, in relation to dense object.
4. Extremely thin structures like menicus and intervertebral disc may be difficult to identify in sections and also in the scan thus they should be kept in mind while interpreting the scans.
5. The shadows of the object in the CT scans will produce a varying spectrum of light which vary from extreme white to extreme black with 64 different type of shades. The appearance of this grey nature will depend on the density/volume of the object which depends on the ionic composition of the object which will be proportional to the linear absorb coefficient or attenuation coefficient of the object. (Enclosure: I B)

Attenuation coefficient of the object is the permeability of the tissue for the x-rays hence the objects with higher density will appear white. Eg: Bone, cardiac muscle, kidney, liver, pancreas and larger blood vessels.

The objects with less density will appear jet black or shades of grey example lungs, adipose tissue. The density value of the objects are standardized taking the density value of water as zero houns field units, that of air as -1000 hounsfield units. The density value of compact bone is +250 units spongy bone +130 units, thyroid +70 units, liver +65 units, coagulated blood +80 units, venous blood +55 unit, exudates +18 units, fatty tissue -90 units. (Enclosure VII and VIII ).

Conclusion

1. The knowledge of cross sectional anatomy is of use for the sonologists to determine the size the location, the shape, the volume of the pathlogical lesions and to guide the clinicians of surgeons for effective therapeutic and surgical measures particularly in laser and microsurgery. Eg: The treatment of the recurring myeloma 4.5 mm in size using sterotactic radiosurgery first of its kind in India was under taken by Dr. Reddy and his team in Apollo Hospital , Madras. The advantage of this is:

   1. It is an out patients procedure.

   2. Does not involve anaesthesia. Saving of head of blood transfusion. (Indian Express dated 9th June 1995)

2. Knowledge of cross sectional anatomy will help in the identification of certain areas which have not made their significance in Gross anatomy Eg: Inferior aortic recess. Right pulmonic recess of transverse sinus.
3. It will be of immense help in the diagnosis of congenital disease of heart and gastro intestinal tract.
4. Hence the knowledge of cross sectional anatomy is a must for everyman and woman of the medical profession without which the practice of medicine will be a failure.
5. The knowledge of cross sectional anatomy can be obtained only in the department of anatomy not anywhere else, the knowledge of cross sectional anatomy can be imported to the undergraduate and post graduate courses irrespective of the inclusion- non inclusion in the curriculum of teaching.
6. Anatomical society of Karnataka being a professional body should recommend to the academic councils of all the Universities in the state and the country and to the Medical council of India to include cross sectional anatomy in the curriculum like that existing in USA wherein they have made the study of cross sectional anatomy compulsory for surgical residency programmer.
7. I may be permitted by this August house to suggest to the Association of anatomists of Karnataka to initiate conduction of workshops in cross sectional anatomy.

I may be permitted to conclude by saying,

“Strange how much you have got to know before realizing how little you know!”

References

1. A cross sectional approach to anatomy by Roy R Peterson
2. Cross sectional anatomy- An atlas for computerized tomography by Robert S Ledley
3. Whole body computerized tomography by O.H Wegener
4. Cross sectional anatomy, computerized tomography and ultrasound correlation by Barbara L. Carter
5. Cross sectional anatomy: Preparation of teaching specimens: by R.D. Peppler Anatomical record July 1993
6. An educational method of cross sectional anatomy combined with gross anatomic practice by Saraki K Dept of anatomy Yokohama City University School of Medicine Japan June 1994

Dr Ramachandrappa
Deputy Registrar, Rajiv Gandhi University of Health Sciences.
Karnataka, Bangalore
Formerly Professor and Head of the Department
Department of Anatomy
Dr B R Ambedekar Medical College, Bangalore

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