Scrotal Scintigraphy and Quantitative Imaging Approaches in the Evaluation of Patients with Acute Scrotal Pain

INTRODUCTION

Acute scrotal pain is an important clinical presentation that necessitates great care with a rapid, definite diagnosis and management as it may represent a surgical emergency that needs immediate interference to save the affected testis. It may also be due to other medical pathological disorders that need medical treatment.

Of the different causes of acute scrotal pain, we are concerned more with the detection of cases with testicular torsion because it is a true urological emergency and must be differentiated from other pathological conditions presented with acute testicular pain. Any delay in diagnosis and management can lead to a loss of the affected testicle.

Although testicular torsion can occur at any age, including the prenatal and perinatal periods, it most commonly occurs in adolescent males. It is the most frequent cause of testicle loss in that age [1].

Testicular torsion is most often observed in males younger than 30 years old. Incidence in males younger than 25 years is approximately 1 in 4000, with the most commonly affected age range between 12 and 18 years. The peak age is 14 years, although a smaller peak also occurs during the first year of life [2].

Torsion most often involves the left testicle. Of the cases of testicular torsion that occur in the neonatal population, 70% occur prenatally and 30% postnatally [3]. The incidence of testicular torsion in cases with acute scrotal pain is 17% [4].

There are 2 forms of testicular torsion. The first is intravaginal torsion seen in adults and children. The specific initiators are unknown but it is suggested that the low insertion of cremasteric fibers leads to pulling and upward rotation of the cord and testis. Most commonly, the tunica vaginalis is overly capacious, completely surrounding the testis and epididymis, investing the cord at a higher-than-normal position (bell-clapped deformity) [5]. This defect is usually bilateral, placing the other testis at risk, as well [6]. The second is extravaginal torsion seen in neonates, where the affected testis in acute torsion becomes ischemic due to the interruption of blood flow through the twisted vascular pedicle [7].

Generally, in both types, edema, hemorrhage, and the irreversible loss of spermatogenic function follows acute testicular torsion unless perfusion is restored within 6 to 12 hours [8]. So, the condition is considered a urological emergency that needs immediate diagnosis. However, the clinical diagnosis of acute testicular torsion has many limitations as the history of sudden onset unilateral scrotal pain and swelling can occur in other conditions, such as acute eipdidimo-orhitis. Although a physical examination is useful in the diagnosis of testicular lesions, it is imperfect in diagnosing acute testicular torsion as it may be difficult to be palpated since the testis is very tender and the patient is often in significant discomfort [9].

Accurate diagnostic tools in acute testicular torsion are necessary, especially if the clinical diagnosis is equivocal. In this manner, imaging studies are emerging as rapid, useful diagnostic tools for radionuclide scans of the testicles. This is very helpful in assessing blood flow, which could differentiate torsion from other pathological conditions.

Scrotal scintigraphy, in many studies, has sensitivity and a specificity of more than 90% in detecting acute testicular torsion depending on decreased testicular blood flow, demonstrated as decreased uptake to the affected testicle [10].

However, until now all, these studies have no standard values to compare with the other testicle to increase its specificity and diagnostic accuracy. So, in this study, we are going to find a standard, fixed-comparison region of interest that couldn’t be affected by similar or other pathological disorders.

METHODS

Patients with acute scrotal pain were sent to the nuclear medicine laboratory in King Fahd Specialist Hospital for evaluation after a scrotal ultrasound (US) had been performed. Full and clear instructions were given to patients about the nature of the study and its role in achieving an accurate diagnosis for their underlying pathological condition.

SCROTAL SCINTIGRAPHY TECHNIQUE AND IMAGING PROTOCOL

By the aid of state-of-the-art, wide-field gamma cameras fitted with a low-energy collimator, patients lay supine under the gamma camera detector. The penis was taped upwards at the anterior abdominal wall and both thighs were separated away with a small pillow between to allow proper and fixed separation. The scrotum was then symmetrically adjusted over this support with a thin lead marker fixed between both scrotal compartments for proper anatomical localization.

Technetium pertechnetate (99mTcO4) was injected intravenously in a bolus dose of 10 to 15 mCi (370 to 550 MBq); meanwhile, the gamma camera, via the acquisition computer system, took 2 serial dynamic image sets as follows:

• The first dynamic set of images set was taken every 2 seconds for 2 minutes (60 vascular flow images).
• The second dynamic set of images was every 60 seconds for 10 minutes (10 images).

A static image for 500 k counts was taken after the end of the dynamic studies.

Time-activity curves, as well as different statistical count data, were generated by the aid of computer systems connected to the machine for processing of the acquired images and data.

Analysis of the dynamic data and time-activity curve to create numeric data calculating the ratio between testicular radioactivity count/background radioactivity count was done at the same time with ordinary reading criteria for interpretation of the static images to diagnose and differentiate the underlying pathological disorders. Results were compared with that of the ultrasound, both operative as well as histopathological studies done postoperative.

RESULTS

A prospective study of 40 male patients within the age range of 7 to 21 years (mean 13.5 ± 5.3) were included in this study over a period of 2 years from November 2008 to November 2010. The main complaint was acute testicular pain in all patients (100%). 24 cases (60%) had left-side testicular pain, whereas right-side pain was noticed in 16 cases (40%).

22 cases (45%) had a past history of similar attacks. A history of trauma was encountered in 9 cases (22.5%) while 9 cases (22.5%) had a past history of recurrent inflammatory process proven by previous ultrasonography. Six cases (18%) were known to have varicocele and 13 cases (32.5%) proved to have testicular torsion after surgical exploration.

The numeric data showed that there was a correlation and a significant critical cut-off ratio between testicular radioactivity count/background radioactivity count determined by symmetrical regions of interest drawn at both the testis, as well as the medial aspect of the ipsilateral thigh. This cut-off figure was 1.45 for the normal testicular radiotracer uptake in comparison to the ipsilateral medial aspect of the thigh, which represents the background radioactivity uptake. This also correlated significantly with the clinical as well as the sonographic data (p value = 0.034, significant). This cut-off figure can be calculated by taking the mean value for the count rate per pixel at the regions of interest drawn with the same sizes at left and right testis, as well as the background, and dividing it to the comparable number at the ipsilateral thigh activity.

For the case in Figure 1, the mean for ROI-1 (drawn at the left testis) is (1330 + 2080 = 3410/2 = 1705), whereas, for the right testis, ROI-2 is (1275 + 2161 = 3436/2 = 1718). The background ROI-3 is (1120 + 1215 = 2335/2 = 1167).

• Left testis count rate/Bg count rate = 1705/1167 = 1.46
• Right testis count rate/Bg count rate = 1718/1167 = 1.47

Below this figure there was a high certainty of impaired testicular perfusion and uptake that suggests impaired blood flow to the affected testis.

A mean ratio of <1.2 (found in 12 cases) was indicative of testicular torsion, impaired vascular flow to the testis, and impaired testicular uptake of radioactivity. This also correlated significantly with the clinical, sonographic data and operative data, as well as the histopathological data done postoperatively (p value = 0.00041).

For the case in Figure 2, the mean for ROI-1 (drawn at the left testis) is (7671 + 10233 = 17904/2 = 8952), whereas, for the right testis, ROI-2 is (5952 + 7146 = 13098/2 = 6549). The background ROI-3 is (5021 + 5340 = 10361/2 = 5180).

• Left testis count rate/Bg count rate = 8952/5180 = 1.7
• Right testis count rate/Bg count rate = 6549/5180 = 1.2

Moreover, the higher ratios >1.5 (found in 18 cases) was suggestive of acute inflammatory disorders, such as epididymo orchitis or varicocele with no clear cut-off figure to differentiate between these 2 pathological conditions (p value = 0.21).

This technique concludes that the sensitivity of this technique’s reach is 92.3%, with a specificity of 96.4% and diagnostic accuracy at 95.1% in the diagnosis of acute testicular torsion.

DISCUSSION

Acute scrotal pain is a very common presenting symptom for many testicular pathological disorders ranging from mild, non-emergency conditions to severe emergency situations that necessitate rapid surgical interference—testicular torsion especially if there are 3 or more complete spermatic cord rotations. Testicular infarction ensues within 2 hours, whereas a single, 360-degree twist permits testicular viability for 12 to 24 hours. Surgical testicular-salvage rates vary from 20 to 90% and are inversely related to the symptom duration. Proper diagnosis necessitates the presence of simple, readily available, rapid and definite diagnostic tools to reach the proper diagnosis.

Scrotal scintigraphy in many studies has a sensitivity of 90% and a specificity of 80% in detecting testicular blood flow when it demonstrates decreased uptake to the affected testicle [10].

In many nuclear medicine studies, and through the aid of advanced computer systems, there is much standardized numeric data and curves in the imaging of many organs and systems that could facilitate reaching a definite and proper diagnosis, as well as creating a baseline figure for follow-up later on. The most popular example is assessing the glomerular filtration rate (GFR) in global kidney functions and the split functions of both kidneys separately [11].

Another example is in assessing the degree of uptake of radiotracers via the functioning tumor cells in comparison to the normal cells. This creates a cut-off ratio and figure (3.5:1) to diagnose malignant cells and differentiate them from the surrounding normal cells, showing the affinity for uptake as well as retention of radioactivity inside cells [12]. However, until now, laboratories have no standard values in the imaging and diagnosis of a more critical situation like testicular torsion. Diagnosis is done (qualitatively) by visual and subjective comparisons of the other testicle and may have a similar pathological status (hypoperfusion) or other pathological conditions, such as varicocele (hyperperfusion), which is beside the intra-observer variability in interpreting image data.

To increase its sensitivity, specificity, and its diagnostic accuracy, we tried to compare the testicular uptake of radioactivity with that uptake at the ipsilateral medial aspect of the thigh that represents the background radioactivity, and, hence, creates a ratio between the uptake at the above-mentioned regions of interest (ROI).

By this method, we gain 2 benefits. The first is that we can overcome any misinterpretation due to the presence of any coincidental pathological disorders in the other testis. The second is achieving a clear and definite numeric figure that could help differentiate different pathological disorders that may affect the testis.

Acute testicular pain may be due to acute inflammatory processes that associate with marked hyperemia and increased blood flow aimed at bringing many antibodies and leukocytes in response to the release of inflammatory mediators. This pathological condition appears in the scrotal scintigraphy (Figure 1 and Figure 2).

The dynamic study showed increased radiotracer flow rates to the affected testis in response to hyperemia.

Enhanced radiotracer uptake by the affected testis, in response to the inflammatory affection of the interstitial cells and tissues, causes pooling and stagnation of radioactivity in the interstitium. These 2 criteria lead to increased and enhanced radiotracer uptake by the affected testis, compared to the contra-lateral normal testis or the background radioactivity at the medial aspect of the thigh.

So, the increased ratio of radiotracer uptake between the affected testis and the background radioactivity become more than 1.45, which proved to be the cut-off figure for the normal testicular radioactivity uptake/background radioactivity uptake.

In comparison, in the presence of acute testicular torsion, there is decreased blood flow to the affected testis due to occlusion of the feeding vessels and, consequently, decreased testicular perfusion.

Scan-wise there is a marked decreased radiotracer flow rate to the affected testis and marked impairment of the testicular handle of radiotracers in the static images. This condition significantly decreased the ratio between the testicular tissue radioactivity uptakes in comparison to the background radioactivity. This ratio is <1. This background uptake level at the affected scrotal compartment is attributed to the scrotal skin uptake itself and not the testis.

Our study is in accordance with the work of Yuan and his group [13] who concluded that scrotal scintigraphy had significantly higher sensitivity. A comparison to scrotal ultrasonography in the detection of acute testicular torsion (94% versus 49%) was also demonstrated in the study of Wu et al. [14]. Also, our study has superior results than the study of Nussbaum and his colleagues [15] who demonstrated diagnostic accuracy of 87% for scrotal scintigraphy in the diagnosis of acute testicular torsion in 46 children with acute scrotal pain.

However, all of the previous studies used the qualitative method for evaluating the scintigraphic picture, which is subjective in counting the degree of radiotracer testicular uptake with a great possibility of intraobserver variability and, therefore, decreased diagnostic accuracy of the procedure. Our work used the quantitative method for evaluating the scintigraphic picture, which is objective in counting the degree of radiotracer testicular uptake, eliminating the bias of any suggestion and misinterpretation reflected on increased sensitivity and specificity of the scrotal scintigraphy by our quantitative method.

In conclusion, this ratio is highly significant and has a sensitivity of 92.3%, a specificity of nearly 97%, and diagnostic accuracy of 95%, which indicates the great importance of this technique in the diagnosis and differentiation of different pathological disorders that affect the testis and cause acute scrotal pain.

Table 1

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