The standards of an ultrasound examination of the prostate gland. Part 1

Abstract

The article discusses the principles of the proper performance of the ultrasound examination of the prostate gland. The paper has been divided into two parts: the general one and the detailed one. The first part presents the necessary requirements referring to the ultrasound apparatus for performing transabdominal examinations of the urinary bladder and the prostate gland as well as for transrectal examinations of the prostate gland. The paper also describes the techniques of performing both examinations together with the methods of measuring the capacity of the urinary bladder and the volume of the prostate gland. It also mentions the most frequent indications for performing the examinations as well as diagnostic algorithms applied in case of finding irregularities. The transabdominal ultrasonography is a part of the examination of the abdominal organs and it should be performed in patients complaining of dysuric symptoms. An addition to the examination, especially when the prostate gland is enlarged, should be the measurement of the capacity of the urinary bladder and the assessment of the amount of residual urine after voiding. The indications for the endosonographic examination of the prostate gland are patological changes found in the per rectum examination, elevated concentration of the prostate-specific antigen in the blood serum, cancer and inflammations of the prostate gland if an abscess is suspected, qualification for surgery in the course of benign prostatic hyperplasia and the diagnostics of disorders of ejaculation. A standard procedure performed in case of prostate cancer for the purpose of obtaining specimens for the histopathology examination is biopsy carried out with transrectal ultrasound imaging. The paper presents the indications and techniques of performing prostate biopsy, as well as the types of biopsies together with the necessary preparation and the protection against its side effects for the patient. The paper also lists the necessary elements of the description of the presented procedures. The second part of the paper presents the application of the ultrasound examination in benign prostatic hyperplasia, in cases of inflammation and in prostate cancer.

The ultrasound examination of the prostate gland performed through the abdominal integuments and the assessment of the amount of residual urine in the urinal bladder

The ultrasound examination of the prostate gland performed through the abdominal integuments (transabdominal ultrasonography, TAUS) is a part of the examination of the abdominal organs and it should be mandatorily performed especially in patients in whom dysuric symptoms are found such as frequent urination during day and night, urging needs to urinate, the feeling that the urinary bladder has not been completely emptied. An addition to the examination – especially when the prostate gland is enlarged – should be the measurement of the capacity of the urinary bladder and the assessment of the amount of residual urine after voiding^(1–3).

The apparatus

Transabdominal ultrasonography of the prostate gland in adults is performed using linear, sector or convex transducers with frequencies ranging from 2 to 5 MHz or wideband transducers with the frequency range from 2 to 5 MHz. The sector and convex transducers are more convenient, especially during performing longitudinal sections, because they may be inserted behind the pubic symphysis thus allowing to obtain the image of the entire urinary bladder.

The examination technique

The examination is performed with the patient positioned on the back. The condition for a properly performed examination is a well filled urinary bladder. If the bladder is not well filled the patient should be given fluid to drink and, if necessary, a tablet of Furosemide in order to accelerate the diuresis. A well filled urine bladder constitutes an “acoustic window” for the ultrasound waves penetrating the abdominal cavity to the prostate gland.

The examination starts by applying the transducer transversely just above the pubic symphysis. Next, the transducer is slid in a fan-like movement in search for the largest section of the prostate gland. It is necessary to measure the width of the prostate (W), assess its symmetry, evaluate the size of the third lobe of the prostate and measure the scope of its protrusion into the lumen of the urinary bladder, taking the level of the wall of the bladder as the starting point for the measurement. Some of the researchers measure the height (H) of the bladder on a transverse section, however most recommend performing measurements on a longitudinal section. Next, after turning the transducer by 90º, longitudinal (sagittal) sections are obtained. The height (H) and the length (L) of the prostate gland should be measured on the largest longitudinal section. The size of the protrusion of the prostate into the lumen of the urinary bladder is also evaluated on this section. If the anatomical conditions do not allow for this (in obese patients) it is possible to only measure and provide two dimensions of the prostate gland in the description – the height (H) and the width (W).

Many methods of measuring the volume of the prostate gland have been described. The most common method is the one applying the formula for the volume of the ellipsoid. It is assumed that the prostate gland, similarly as the urinary bladder, has got a shape most resembling an ellipsoid. However the prostate does not change its shape, as it is in the case of the urinary bladder, depending on the degree to which it is filled. Therefore the measurements are more accurate than the measurements of the capacity of the urinary bladder. The formula for the volume of the ellipsoid is as follows:

V (the volume of the prostate gland) = Π/6 × height (H) × width (W) × length (L)

Π/6 = 1/6 Π = 0,5236

This is a method of a biplane measurement because on one section the measurement of the width and the height is performed and on the second one – the one which is orthogonal to the first section – the length measurement is performed. Such measurements are performed in men with dysuric symptoms, e.g. resulting from benign prostatic hyperplasia. In this group of patients during the examination it is necessary to measure the volume of the residual urine after voiding. After the examination of the prostate gland performed with a full urine bladder the patient should urinate. The measurement is performed if the result of the ultrasound examination or the history taken from the patient suggest a bladder outlet obstruction or if the clinician orders the performing of the examination.

Many methods of measuring the capacity of the urinary bladder and of evaluating the amount of residual urine after voiding have been described. The most common one, similarly as in case of calculating the volume of the prostate gland, is the measurement method applying the formula for the volume of the ellipsoide. It is assumed that the urinary bladder has the shape most resembling an ellipsoid. On the basis of this assumption one can deduce that the more the bladder is filled, the more the ultrasound measurements are close to real values. The measurement of the width of the bladder (W) is performed on the transverse section, and the measurement of its length (L) – on the longitudinal section. The measurement of its height may be performed on the transverse or the longitudinal section, however it is necessary to remember to mark the largest distance between the examined walls. If such measurements are performed on a bladder which is maximally filled, the effect will be the measurement of the capacity of the bladder; if they are performed after urination, the effect will be the measurement of the residual urine after voiding^(4–7).

In the transabdominal examination one should not evaluate the echogenicity of the prostate gland nor potential pathological changes within its scope. The transabdominal examination in obese patients, in patients with aches of the abdominal cavity and in case of a lack of possibility for the proper filling of the urinary bladder does not always allow for a reliable assessment of the volume of the gland. Every time any irregularities are found, e.g. in case of an enlargement of the gland, it is necessary to order an examination performed with an endorectal transducer.

Results

The description of an ultrasound examination of the prostate gland should include: the dimensions of the gland, the evaluation of its shape and symmetry, the description of its boundaries and the volume of residual urine after voiding. In case of suspected pathology, it should include a recommendation for an examination of the prostate gland using an endorectal transducer. The description should end with diagnostic conclusions, if necessary, with a recommendation of an examination using an endorectal transducer and of a medical consultation with a urologist. The results of the calculations of the volume of the prostate gland should be provided in millimeters. The supplementation of the description of the examination should always be the photographic documentation of all the abnormal changes found in the prostate gland and the documentation referring to the performed measurements.

The transrectal ultrasonography of the prostate gland

The indications for performing an endosonographic examination of the prostate gland using an endorectal transducer are: pathological changes found during the palpation examination performed per rectum (an induration, a lump, asymmetry), elevated concentration of the prostate-specific antigen (PSA) in the blood serum, benign prostatic hyperplasia (qualification for surgery), inflammation of the prostate gland, prostate abscess, the diagnostics of disorders of ejaculation and prostate cancer (qualification for surgery or radiotherapy, monitoring of the non-operative treatment, the search for local recurrence after radical surgery)⁽⁸⁾.

The apparatus

The ultrasound examination of the prostate gland should be performed using endorectal transducers with a frequency of 8 MHz and higher, preferably 10 MHz, electronic linear transducers or convex transducers. The best transducer for the examination is a transducer which demonstrates the transverse and the longitudinal section of the prostate simultaneously, the so called biplane transducer. It allows the precise localization of changes found in the prostate; it enables the performing of a biopsy of precisely specified areas of prostate gland. The endorectal transducer should have the option of a power doppler or a color doppler for the assessment of the vascularization of the prostate gland.

The ultrasound machine with 3D software allows for creating three-dimensional images of the prostate gland. This enables the performing of a more detailed examination of the prostate presenting it in a new coronal section, which was not possible to achieve until now. This allows for very detailed examining of the prostate gland, its capsule, its apex, its base with the seminal vesicles, the neurovascular bundles and for the spatial evaluation of its vascularization. It is advisable to also take this option into consideration while purchasing a new machine.

The examination technique

Every examination performed using an endorectal transducer should be preceded by a digital rectal examination (DRE) of the prostate gland. It is advisable that this examination is performed by the same person who is next going to carry out the ultrasound examination. The transrectal ultrasonography (TRUS) of the prostate gland should be correlated with the clinical per rectum examination.

It is advisable to determine the level of the prostate-specific antigen (PSA) in the blood serum before performing the ultrasound examination using the endorectal transducer.

The examination is performed with the patient laying on his left side, with legs bent in the knees and pulled to the chest. A rubber protective cap should be placed on the transducer with a little gel before every examination.

The transducer is delicately inserted into the rectum while observing the ultrasound machine screen.

First the measurements of the prostate are performed. The width (W) is measured on the transverse section, after finding the largest section and next the height (H) and the length (L) are measured on the largest longitudinal section. It is necessary to precisely define the lower measurement boundary, i.e. the apex of the prostate or the beginning of the urethra within the bulb. Some researchers measure the height (H) on the transverse section. The majority of modern ultrasound machines perform calculations of the volume of the gland automatically. They apply the formula for the volume of the ellipsiod quoted in the previous chapter^(7–9).

The next step is the evaluation of the shape, the symmetry of the gland, the integrity of the capsule, the echogenicity of each of the zones of the gland (described by McNeal), basing on the detailed transverse, longitudinal and intermediate sections which were developed. Attention is paid to areas of reduced and increased echogenicity – focal or diffuse. Evaluation is also performed in reference to the periprostatic structures (the adipose tissue, vascular plexi), the seminal vesicles – their dimensions (length and width), structure, symmetry and the angle between the vesicle and the prostate – as well as the ampullae of the ducti deferens.

Every abnormal change should be accurately measured and described with paying special attention to the echogenicity, the location, the shape and the demarcation from the adjacent structures.

A valuable supplementation of the entire examination is the assessment of the vascularization of the prostate and the adjacent organs, including the neurovascular bundles, using a color doppler or a power doppler. Neoplastic changes are often accompanied by angioneogenesis, hence the strong densifying of the blood vessel mesh in the neoplasm development areas. This facilitates the localizing of the neoplasm and it is specially useful during the biopsy of the prostate.

Another very useful extension of the endorectal examination is the evaluation of the firmness (consistency) of the prostate tissue performed using elastography. If the ultrasound machine provides the possibility to perform this examination it should be mandatorily performed, because it allows for demonstrating areas of more firm consistency, which may be cancers and which are isoechogenic in classical ultrasonography and thus may not be noticed. This examination increases the sensitivity of the endorectal ultrasound diagnostics of the prostate, which is especially important and useful for the localization of neoplastic focuses during the biopsy of the gland^(10–12).

In a case when a prostate of quite a big size is found in men in whom there is a suspicion of the occurrence of residual urine after voiding, there is a need to assess the urinary bladder. In such cases one should underline the need to perform an ultrasound examination of the abdominal cavity (the evaluation of the urinary bladder and the kidneys – if such an examination had not been carried out before).

3D transrectal ultrasonography (TRUS 3D) slightly changed the research methodology. After the carrying out of the basic 2D endosonographic examination the 3D option is turned on and the acquisition of images is performed by sliding the transducer in a steady and smooth motion so that the entire prostate gland is covered – from the apex to the base together with the base with the seminal vesicles, and the issues surrounding it. The data saved in the form of units of volume, the so called voxels, are elaborated after the examination. The obtained images are spatial (three-dimensional). This allows for obtaining any sections of the prostate. As a result, more accurate images are obtained and proper computer processing allows for obtaining a whole range of new details referring to the morphology of the prostate, its surrounding and the seminal vesicles. This examination is especially useful in searching for places where the neoplasm extends beyond the prostate gland, which is related to the assessment of the local staging (T).

The description of the examination result

The description of the ultrasound examination of the prostate gland should include: the dimensions of the gland, the volume (in millimeters), the assessment of its shape, symmetry, the assessment of the size of particular zones – especially the peripheral and transition zones, a description of the echogenicity and the assessment of the integrity of the capsule. Moreover the description should include the assessment of the seminal vesicles, their size, echogenicity and the symmetry of the angles between the vesicles and the prostate, as well as the assessment of the ampullae of the ducti deferens. If examinations were performed with the application of the doppler, it is necessary to describe the symmetry of the vascularization, the presence of the flow in neurovascular bundles, the areas where significant densifying of blood vessels was observed.

In case of finding pathological changes it is always necessary to describe their morphology, their location and to suggest further procedure.

The supplementation of the description of the examination should always be photo documentation imaging the abnormal changes.

Biopsy of the prostate gland

The biopsy of the prostate gland performed under ultrasound control using a tru-cut needle, for example of the thickness of 18 gauge providing histological specimens is a standard procedure in the diagnostics of prostate cancer. The histopathological diagnosis of cancer is the necessary condition for beginning both radical an palliative treatment.

The indications for performing a biopsy of the prostate are: pathological changes found during the digital rectal examination (an induration, a lump, asymmetry), elevated concentration of the prostate-specific antigen (PSA) in the blood serum, evident changes of the structure of the gland found in the ultrasound examination, especially in the group of patients who are at risk due to a family history of prostate cancer. Transrectal biopsy is also performed for the purpose of the diagnostics of local recurrences after radical surgical treatment^(13–16).

The aim of the biopsy is: to obtain a histopathological diagnosis, to assess the degree of the impairment of cytoarchitectonics according to the Gleason score, to evaluate the histological malignancy grading and, in selected cases, when there is a suspicion of the expansion of the neoplasm outside the gland to assess the local staging (T).

The apparatus

Both the ultrasound examination of the prostate gland preceding the biopsy and the biopsy itself carried out under ultrasound control must be performed using endorectal transducers with a frequency of 6 MHz and higher, preferably 10 MHz, electronic linear ones – which demonstrate the longitudinal section of the prostate gland – or convex transducers – which demonstrate the transverse section.

The perfect transducer for performing a biopsy of the prostate is a transducer allowing for the simultaneous biplane imaging of the prostate gland. The imaging of the transverse section and the longitudinal section of the prostate demonstrated on the monitor screen in real time allows for very precise taking of specimens from strictly determined areas. The describing of the areas from which the specimens are taken grants the possibility to perform a precise re-biopsy in case of finding pre-cancerous conditions. It would be good if there was a possibility to perform a doppler examination and an elastography examination of the prostate tissue using the transducer.

The endorectal transducer must be equipped with an internal bioptic channel or an attached biopsy needle guide which corresponds with the biopsy track shown on the screen of the ultrasound machine in the form of a line of light spots.

A biopsy is performed using a tru-cut cutting needle, preferably one with a diameter of 18 gauge. This needle allows for obtaining bioptic specimens of ca. 15 mm of length and ca. 1 mm of thickness (diameter). The needle is placed in the so called automatic biopsy gun, which after loading (stretching the spring), unlocking and pressing the trigger allows for taking bioptic specimens. During the biopsy, in a short time the tru-cut needle performs a sliding motion consisting of two stages. In the first stage the needle core (the arrowhead) with a special indentation is pierced into the tissue, in the second stage the external cutting part cuts off the piece of tissue which is present in the indentation of the arrowhead.

The examination technique

The biopsy of the prostate gland is performed in the treatment room with taking into consideration all the rules of aseptics and antiseptics. The needles used for the biopsy as well as the needle guide are sterile. Biopsy needles are disposable.

The physician carrying out the biopsy of the prostate is obliged to take the medical history from the patient before performing the procedure. It is especially important to find out whether the patient does not take antithrombotic medications. This is an absolute contraindication to performing a biopsy. The patient should stop taking antiplatelet medications 5 days before the biopsy procedure and he should restart taking them after 3 days from the procedure. The patient should stop taking derivatives of coumarin 5 days before the procedure and he should resume taking them on the third day after the procedure. After stopping taking antiplatelet medications the patients suffering from thromboembolic disease should take semi-synthetic, low molecular weight heparin, for example Fraxiparine or Clexane.

Prostate biopsy is a procedure which causes a potential risk of an infection. Due to this fact it is necessary to perform this procedure with antimicrobial protection. The European Association of Urology recommends the oral or intravenous use of fluoroquinolones, for example ciprofloxacin 1 capsule (500 mg) 2 times a day. Recently growing resistance to fluoroquinolones is observed. In this situation microbiologists recommend using Biseptol 960 1 tablet 2 times a day or Cefuroxime 1 tablet (500) two times a day, also orally. These medications should be taken by the patient not later than 2 hours before the procedure and the patient should continue taking them for 5 days after the procedure^(15–17). Recently a biopsy needle has been applied which is covered with a polymer releasing antibiotics (amikacin or ciprofloxacin) directly to the prostate gland during the biopsy (the drug-eluting biopsy needle, DEBN). Preliminary observations have shown effective antibacterial activity precisely in the place where the specimens are taken⁽¹⁸⁾.

In some hospitals an enema is performed on the day of the procedure in order to purify the rectum from fecal masses. However in most cases natural defecation is enough.

On taking the medical history, before the biopsy, it is necessary to inform the patient about the purpose of the examination, about the purpose and technique of the examination and possible complications such as the presence of a small amount of blood in the stool, in the urine for a few days, in the semen (sometimes even for several weeks) and possible infection. A rare complication are prostate hematoma and prostatic abscess developing as a result of it.

Before the procedure, the patient must provide written consent for the procedure and he must follow the post-procedure recommendations.

Every inserting of the endorectal transducer into the rectum should be preceded by a digital rectal examination (DRE) of the prostate gland. This examination should be performed by the same person who carries out the ultrasound examination and the biopsy.

The examination is performed with the patient lying on his left side, with legs bent in the knees and pulled to the chest. A sterile rubber protective cap should be placed on the ultrasound transducer with a little gel before every examination. Next, a sterile guide for the biopsy needle is mounted and one more sterile rubber protective cap is inserted on the guide. All this is delicately inserted into the rectum under control of sight with simultaneous observing of the ultrasound machine screen.

After the precise ultrasound examination of the gland, specimens are taken. Usually no special local anesthesia is necessary. However, in some cases, 1–2 ml of 1% solution of lignocaine may be administered under the control of TRUS in the area of the neurovascular bundles on each side.

After the needle is inserted into the gland, it is guided to the boundary of the area from which the specimen is to be taken. The triggering of the biopsy automaton causes the moving of the needle forward and the taking of the specimen.

The following biopsy types may be distinguished:

• A formal biopsy is a biopsy performed in patients in whom radical treatment is not planned. These are usually patients with an advanced clinical level of the development of the disease and the diagnosis is to enable the implementation of palliative treatment.

In clinical practice, a diagnostic biopsy is expected to provide much more information, i.e. besides the histologic diagnosis also the assessment of the histological malignancy grading, the assessment of the level of impairment of the cytoarchitectonics according to Gleason and the evaluation of the extent and the local staging (T). This requirements may be met by:

• A mapping biopsy – is based on taking from 12 to over 20 specimens from strictly defined, routine locations of the prostate gland in which the probability of the existence of cancer is the highest – the side areas of the peripheral zone – the area of the base, the middle part and the apex of the gland. A biopsy of this kind is performed when neither DRE nor TRUS suggest the existence of a neoplasm, and the suspicion of its existence is based on an elevated PSA level. Some authors, who decide on the number of specimens depending on the size of the prostate, apply the following calculation method: in small glands of 40 cm³ of volume or less they take 6 specimens, they take 8 specimens if the volume of the gland is between 40–100 cm³ and 10 specimens if the volume of the prostate is over 100 cm³.

For the need of determining the number of biopsy specimens some authors introduced the concept of “biopsy density” understood as the ratio of the number of the collected tissue specimens (N) to the rectal surface area of the prostate. The rectal surface area was likened to an ellipse and it was calculated using the formula for the surface area of an ellipse, where the minor axis of the ellipse is the width of the prostate (W) and the major axis – the length of the prostate (L)^{(13, 16)}.

The rectal surface area (S):

$$\text{S}=\frac{\Pi \times \text{W}\times \text{L}}{4}$$

The formula for the density of the biopsy (^TRUScore B × D) therefore takes the following form:

$${}^{\text{TRUS}}\text{core\hspace{0.17em}B}\times \text{D}=\frac{\text{4}\times \text{N}}{\text{Π}\times \text{W}\times \text{L}}$$

It was experimentally found that the chance of detecting prostate cancer increases nearly four times when the biopsy density is equal 0.75 or more. Therefore the formula for the minimum number of specimens for a given size of the prostate takes the following form:

$$\text{N}=\frac{\text{0,75}\times \text{Π}\times \text{W}\times \text{L}}{\text{4}}$$

During re-biopsies a higher number of biopsy specimens is collected, with taking into consideration especially the local pathologies found in previous biopsies.

• A biopsy targeted at a lesion consists in taking specimens from a palpable tumor or from: 1) an abnormality of the architectonics of the prostate in the form of hypo- or hyperechogenic areas visible in the TRUS or 2) areas of densification of the vascular mesh demonstrated in doppler examinations or 3) areas of more firm consistency shown in the elastographic examination. If the patient is a candidate for radical treatment then the targeted biopsy is supplemented with a mapping biopsy.

• Targeted and staging biopsy – is based on taking specimens from typical of a mapping biopsy and additionally from the neurovascular bundles, the seminal vesicles, from the apex of the prostate and from the periprostatic tissue.

The specimens are removed from the needle by the person assisting during the biopsy. This person places them on a strip of sterile paper tissue moistened with physiological saline. The specimens need to be straightened and the peripheral ending has to be marked, e.g. with ink. It is accepted that the total length of the specimens should be at least 60 mm. The paper tissue together with the specimens is placed in a 10% solution of buffered formalin. Placing every specimen in a separate vessel with a precise description of the place from which it was taken (e.g. the base, right side) is especially important in the assessment of the degree of the spread of the neoplastic change within the prostate tissue, and it is most valuable in case of re-biopsies when previously precancerous conditions were found and now a relatively small neoplastic mass is sought. If such procedure is not possible then specimens from the right and the left lobe are placed separately and they are precisely marked.

The information present on the referral form to the department of pathology include not only the patient’s personal data but also his age and the level of the prostate-specific antigen in the blood serum as well as the information about the possible treatment (radiotherapy and hormonal therapy).

Procedure description

The description of the biopsy of the prostate gland performed under ultrasound control is made in the medical procedure register book and its copy is placed in the medical history if the patient was subject to one-day hospitalization. Besides typical data such as the name and surname of the patient, his address, birth date, the date of the procedure, the diagnosis, the description should also include the type of the ultrasound machine and the parameters of the transducer used for the procedure. The referral to the department of pathology includes information about the number of the taken specimens and about the areas from which they were taken. The medical history, and later the hospital discharge form should include the recommendations for the antibiotic therapy after the procedure and the information where and when the patient should collect the result of the histopathological examination.

The description of the histopathological examination should include the diagnosis and in case of neoplastic changes: the length of the neoplastic focus in mm, its percentual content in the specimen, the degree of the impairment of the cytoarchitectonics according to the Gleason score, the assessment of the histological malignancy grading, the location of the tumor in relation to the ending of the specimen and the characteristics of the spreading of the infiltration beyond the prostate.

It is also necessary to inform the patient that after receiving the biopsy result, regardless of the histopathologic diagnosis he should consult a urologist in order to determine how to proceed further.

In the recent years an increase of the importance of the magnetic resonance imaging (MRI) has been observed in the diagnosing of neoplastic changes of the prostate gland. Unfortunately, modern technology significantly limits the possibility to perform biopsies under MRI control in real time. The procedure which has become more common relies on MRI examination and next overlaying the MRI image on the ultrasound image in real time using a special technique of digital image processing^{(19, 20)}. The reports present in scientific literature are promising, however they are still at the stage of clinical research and the necessary instruments are expensive and not in the widespread use.

Conflict of interest

Authors do not report any financial or personal connections with other persons or organizations, which might negatively affect the contents of this publication and/or claim authorship rights to this publication.