Spaces in the Cranial Cavity

The cranial cavity is divided into smaller spaces called the anterior, middle and posterior fossa each housing separate parts of the brain.

Anterior middle and posterior cranial fossa

48720c01 brain cerebrum cerebral skull anterior cranial fossa middle cranial fossa posterior cranial fossa space position protection bone skull anatomy applied biology TCV

Space Occupation

Since space is limited in the brain space occupation by tumors, blood or edema can affect the patient significantly, sometimes even when small.  In the following example a large benign mass called a meningioma is demonstrated.  The tumor is characteristically grows slowwly over a number of years, progressively taking up the space of normal brain.  As it grows it will also start to push on the brain and may if left untreated push the brain down into the foramen magnum which represents the largest hole in the skull and therefore the  line of least resistance.  The shift can cause pressure on vital centres of the brain and consequently may result in death if left untreated.  This complication in which the brain is pushed downward into the foramen magnum as a result of space occupation is called coning.

Mass with Mass EffectSpace Occupation

The MRI image in transverse plane, shows a large mass in the right frontal lobe region that is pushing structures across the midline.  There is little excess space in the cranial cavity and as this benign meningioma continues to grow it will need more space.  At a critical point it will start to push the brain down through the foramen magnum which is the area of least resistance for the expanding brain.  Left untrated this would press on vital structures and cause death.  Fortunately this disease, meningioma, once diagnosed,  can be cured by surgery. 423078c meningioma  Courtes James Donnelly MD

In the following example, a small metastasis from a renal cell carcinoma occupies little space, but it does cause significant edema in the brain, and it is the edema, rather than the tumor itself that does harm by occupying space.

Renal Cell Carcinoma Metastasis with Edema

In this MRI image of the brain there is a metatsattic nodule (green) that is fairly small measuring just over 2cms, but it has created a ring of edema which is causing mass effect by space occupation (yellow).  This has resulted in subtle space occupation with midline shift. 77300c bilateral RCC mets to lung hemorrhagic mets to brain mass edema mass effect midline shift edema MRI T2 weighted Courtesy Ashley DAvidoff MD copyright 2008

Renal Cell Carcinoma Metastasis with Edema

The long orange line from front to back of the brain represents the midle and the small horizontal orange line shows midline shift of about 4mm.  In this instance steroids would help reduction of the edema and would help reduce the pressure of the space occupation by the edema.

77300c01 bilateral RCC mets to lung hemorrhagic mets to brain mass edema mass effect midline shift edema MRI T2 weighted Courtesy Ashley DAvidoff MD copyright 2008

Non Critical Space Occupation

In the following example a benign bony tumor on the outside of the skull. occupies space but does no harm.

Osteoma

In this 44 year old female a dense space occupying abnormality is located on the back of the skull on the left (overlaid in green in b) and it represents a benign tumor called an osteoma.  At this stage this space occupation does no harm to the patient since it is not pressing on any vital structures. 29107c 44F one occiput occipital bone fx mass ossified dx osteoma neoplasm benign CTscan Davidoff MD

The Chest Cavity

The chest cavity or thoracic cavity, is the space formed inside the rib cage that houses the heart, lungs and mediastinum.  It is connected to the neck at the thoracic inlet, and separated from the abdominal cavity by the diaphragm.  The major organs that lie within the chest cavity include the heart with great vessels, lungs with airways, and the esophagus.  The spinal cord lies posteriorly in its own chamber within the vertebral column and is not traditionally considered part of the thoracic cavity.

The lungs with pleura and airways take up the largest space.  The lung at full inspiration can take up to 6 litres of air.

The Lungs in the Chest

The lungs take up the largest space in the chest.  They are paired and surround the heart (pink) which lies in the centre of the chest and occupies less space.

45770b02c.jpg chest lungs fx normal chest CT anatomy Courtesy Ashley Davidoff MD Davidoff

The lungs surround the heart and are surrounded by by two layers of pleura that are adhered together by a thin layer of fluid.

Spaces in the Chest

The teal green lungs are surrounded by the visceral pleura (pink) pleural space (yellow) and parietal pleura (green) as seen in the both the image on the left and the zoomed image of the layers on the right.32634b10  32634b11b01 The surface of the lung is magnified in the following two images. Fig 1a shows the pink visceral pleura, the yellow pleural space, and the green parietal pleura. Fig 1b shows the costophrenic sulcus where the visceral pleura is absent and two layers of parietal pleura face each other. Courtesy Ashley Davidoff MD . 32634b11b01 32634b11b

 When we inspire, the muscles of the rib cage move out, pull on the outside layer of the pleura, (parietal pleura) which in turn pulls on the inner layer of visceral pleura, which in turn pulls on the lungs, which then expand and pull in fresh air.  The fluid layer in between the two layers of pleura enable the two smooth layers of pleura to adhere together by capillary force in the same way that two wet pieces of smooth glass are inseparable by virtue of the same capillary forces.

Space Occupation

When excessive fluid accumulates in the pleural space it pushes on the lung and causes compression of the normal lung since there is only a limited amount of space in the thoracic cavity.  At some stage, the area that is compressed collapese and becomes airless, and therefore non functional.  Although this is not a life threatening situation it may cause the patient to become short of breath.  In the case of the tension pneumothorax described above, the pressure that accumulates in the pleural space is higher, and for this reason tension pneumothorax can be lethal.  In both instances however the underlying concept is the same – ie space occupation.

Pleural Effusions and Space Occupation Normal on the left and Abnormal on the right

In the above example, the normal lungs are noted on the left and are at their full normal volume.  On the right, the images are of an 88 year old man with bilateral pleural effusions.   Both lungs are reduced in volume caused by the effusions.  The cross sectional images below show the effusions tobetter effect.  The left lung is significantly reduced in volume while the right is only mildly reduced.74238c01 88 year old male bilateral complex effusions pleura pleural space atelecactasis space occupation normal 3D volume rendering CTscan Courtey Ashley DAvidoff MD

Complex Pleural Effusion and Atelectasis

The aerated lungs in the first image are noted in black with the effusions

pleural effusions 74243b01 74242 74242b01 88 year old male complex effusions pleura pleural space thickened pleura thickening unilateral atelecactasis pleural calcification calcified CTscan Courtey Ashley DAvidoff MD

There are many instances of disease and destruction caused by space occupation but another one that comes to mind in the chest is acute coronary thrombosis.  The coronary arteries are basically tubes that deliver blood with life sustaining oxygen to the heart muscle.  If these become blocked with thrombus, the space normally occupied by flowing blood is obstructed with thrombus and flow threfore cannot occur commonly resulting in death of the myocardium, and sometimes death of the patient.

Breast Cancer Invading the Skin Chest Wall and Heart

In this CT scan the breat carcioma (green) has invaded the skin and is exposed on the outside between the thickened pink skin which is thickened due to radiation,  The tumor also invades through the chest wall and has started to erode the pericardium (yellow).  The orange structure is a pad that is acting as a prosthesis in this patient who has had a mastectomy.78387c breast skin heart pericardium invasion space occupation prosthesis CTscan Courtesy Ashley Davidoff MD

Abdominal Cavity

The abdominal cavity, is the space formed by a diaphragm of muscle above and a diaphragm of pelvic muscle below, and usually includes the pelvic cavity.  It mostly houses organs of the gastrointestinal system, genitourinary system, but components of the cardiovascular system, nervous system, endocrine system, reticuloendothelial system, and musculoskeletal system are present to enable the abdominal cavity to connect with the thorax and all the other parts of ther body.

 The major organs that lie within the abdominal cavity include the liver, spleen, adrenals, kidneys, pancreas, gastrointestinal tract, uterus ovaries and prostate and bladder.

Unlike the cranial cavity and the thoracic cavity, there is little bony protection.  Most of the protection comes from more elastic and pliable abdominal musculature.

The spinal cord lies posteriorly in its own chamber within the vertebral column and is not traditionally considered part of the abdominal cavity.

The distinction and border between the abdominal cavity proper and the pelvic cavity is ill defined and vague, and for the sake of discussion it is considered in this text as both part of the abdominal cavity, though a specific subsection of this text will discuss the pelvic cavity separately as well.

Spaces in the Abdomen

The abdominal cavity is divided into the peritoneal cavity and the retroperitoneal cavity.  Each of these is further divided and the detail will be expanded in later modules.  The peritoneal cavity is the larger of the two and it contains almost all the abdominal organs.  The reroperitoneal space contains only the kidneys, ureters, the larger tributaries of the neurovascular system like the aorta, inferior vena cava,  nerves and lymphatic duct.

Space Occupation

The accumulation of fluid or disease processes in the peritoneal cavity is not as life threatening as space occupation described in the chest.  Accumulation of fluid in the abdomen is called ascites and is seen in many conditions.  In the patient shown below the fluid accumulation is due cancer deposits on the peritoneum which is the abdominal lining.

Space Occupation by Fluid and Tumor

This unfortunate 88 year old patient developed ovarian cancer which is a disease that commonly spreads to the peritoneal cavity and a large metastatic mass (green) was both clinically palpable as well as easily seen on CT scan.  The tumor on the peritoneum caused the exudation of fluid which is called ascites.  (yellow overlay) The progressive accumulation of fluid eventually leads to “tense ascites” which is not a life threatening condition , and is mostly felt as discomfort by the patient.  This can be readily relieved by putting a small catheter in the abdominal cavity and draining the fluid.  Unfortunately in this instance the fluid will recur within a week or two.

77370c01 abdomen abdominal cavity ascites ovarian cancer omentum omental cake granulomatous liver disease mass malignant ascites Courtesy Ashley Davidoff MD copyright 2008

Pelvic Cavity

The pelvic cavity, is the space formed by a diaphragm of pelvic muscle below and an open roof above where the distinction between the pelvic cavity and abdominal cavity is vague but best defined by the region of the bony pelvis, including the iliac crests and lumbosacral joint and sacral promontory and the pubic symphisis.  It houses the uterus, ovaries and Fallopian tubes, the bladder and distal ureters, prostate vasa deferentia, sigmoid colon and rectum.  Components of the cardiovascular system, nervous system, endocrine system, reticuloendothelial system, and musculoskeletal system are present to enable the pelvic cavity to connect with all the other parts of ther body.

Similar to the cranial cavity and the thoracic cavity, there is prominent  bony protection by the pelvic bones.

The Normal Pelvis

The bony pelvis is shown in the above CT scan reconstruction.  While the iliac crests and ischia and pubic symphisis are well shown, the sacral component is hidden by parts of the gastrointestinal tract.

71198b01 pelvis bone iliac crest pubic symphisis hip ischial tuberosity pubic bone normal anatomy CTscan 3D Courtesy Ashley Davidoff MD copyright 2008

Spaces in the Pelvis

Most of the pelvic cavity is part of the peritoneal cavity but the retroperitoneum does extend down into the pelvic cavity and thre is also a space called the extraperitoneal space.

Space Occupation

Diseases and fluid accumulation can occupy space in the pelvis in the same way as they may in the abdominal cavity.  Similarly the space occupation is not uually immedietely and emergently life threatening.  The cul de sac is a space that in the female lies between the rectum and uterus, and in the male lies between the bladder and the rectum.  It is the most posterior space in the abdominal-pelvic cavity, and therefore by default is the the first space to accumulate fluid when the patient is imaged in the supine projection.

Space occupation is sometimes (though rarely) a welcoming event.  In the case of the pelvis, the gravid uterus occupies space in the pelvis  and although progressively uncomfortable, the final result is not only desirable but also restoresthe space to its usual owners.

Pregnancy – Physiological and Temporary Space Occupation

The MRI shows a fetus with vertex (head) presentation lying within the gestational sac filled with fluid (white), taking up the space of the pelvic cavity and to some extent the abdominal cavity and displacing normal structures into the abdomen.

46704 abdomen pregnancy fetus baby head brain lungs amniotic cavity amniotic fluid normal anatomy physiology MRI T2 weighted Davidoff MD

Other Spaces

There are other spaces and compartments in the body that do not fit in to the confines of the larger spaces described above.  These include the space of the spinal column, prevertebral spaces, compartments of the muscles bones and joints, the oral cavity, spaces of the neck, the vagina, the external space occupied by the penis and testes, and of course all the microscopic spaces of the tissues, cells and molecules that have a world of their own.

From the Cells to the Cities – Space – a Universal Principle

The artists reconstruction of the space of cells and the the reality of the photograph of space in a seaside town in Cape Town South Africa, are seemingly different, but in reality the same with the universal principle being relevant to both

 of 57927.800 houses town organization position efficiency Muizenberg Cape South Africa Davidoff photography

When one extends the concept of space beyond the body and into homes and towns, cities and countries and then of course planets and the universe – the universality of the principles unfold.  When all is in order – and space is well used, and apportioned then peace and harmony exist.  When on the other hand aggressive space occupation occurs the stories of disorder, disease, death, and misery are told in our history.