Testicular torsion is a surgical emergency in which the cord that feeds a testis twists, pinching off its own blood supply. The testis starts to die within hours of the twist. Ultrasound is brought in to read one thing above all: the blood flow inside the testis. Color flow that is gone inside the testis on the painful side points to a torsion that the operating room has to undo at once. The scan is read against the clock.
The clock that runs on the testis
A torsion is a race. The twist in the cord shuts the blood off. The testis lives on borrowed time from that moment. A testis untwisted within the first few hours is saved in almost every case. After that the chance drops hour by hour. By a full day it is small.
This clock shapes the whole use of ultrasound here. The scan is quick, aimed at the one question of blood flow, and read at the bedside without a wait. A finding of torsion sends the patient to surgery in the same hour. The picture serves only by being fast, since every hour spent on it is an hour off the life of the testis.
The clock also sets a hard rule about the scan. A boy with the classic story and signs of a torsion goes to the operating room on that story alone. The scan is not allowed to delay the knife when the case is clear. Ultrasound is for the case in doubt, where the picture turns a maybe into a yes or a no.
The window is counted from the moment the pain began. The story of when it started is part of the scan, since a testis four hours into a twist is a different prospect from one a day in. The time of onset is asked and noted, and it shapes how hard the testis is fought for.
A torsion is assumed until the scan and the story rule it out.
What torsion does
The spermatic cord twisting on itself, at the left, the twist that chokes the testis’s blood, beside a normal cord and testis at the right. Illustration: Hariadhi, CC BY-SA 4.0.
The testis hangs from a cord that carries its blood in and out. A torsion is a twist of that cord on itself. The twist first pinches the soft veins that drain the testis. Blood backs up. The testis swells. A tighter twist then shuts the stiffer arteries that feed it. The blood supply stops. The testis, cut off from fresh blood, starts to die.
The harm feeds on itself once it starts. The blocked veins let pressure build in the trapped testis. The swelling presses the arteries harder still. The longer the twist holds, the tighter this grip becomes. A testis caught early in the cycle has more to save than one left to swell for hours.
Some testes are built to twist. A normal testis is anchored at the back, fixed to the lining around it. In some boys the testis has no such anchor. It hangs free inside its lining, able to swing and rotate on its cord, a make called the bell-clapper. This build sits on both sides as a rule, which is why the well side is fixed at the same surgery.
The twist comes on chiefly in the years around puberty, in boys and young men. The newborn and the grown man are struck too, at any age. A sudden, severe pain in one testis, often with a sick stomach, is the story that raises the alarm and brings the scan to the bedside.
The story that brings the scan
The pain of a torsion comes on suddenly. A boy is woken by it, or struck by it at rest or at play, a sharp pain in one testis that climbs in minutes. A sick stomach often comes with it. The testis on that side rides high, sore to the touch. The shortened cord has drawn it up. The age of the boy counts too, a torsion sitting high on the list for a teenager with a sudden scrotal pain.
A few signs at the bedside lean toward a torsion. The reflex that draws the testis up when the inner thigh is stroked is often lost on the torsed side. The pain stays sharp and does not ease with rest or a change of position. These signs and the story start the clock. The scan is called to read the flow.
The blood flow that decides it
A color Doppler scan of a torsed testis. The green and yellow box marks where flow is sampled. Inside the box the testis shows no color, its blood choked off at the twist; a single fleck at the upper edge is a vessel outside the testis itself. Absent flow like this is the mark of a torsion. Image: Mak and Tzeng, CC BY 3.0.
The heart of the scan is the blood flow in the testis, read with color or power Doppler. The probe is laid on the testis and the flow is looked for within it. A healthy testis fills with specks of color, the small vessels of its substance lit by the Doppler. A torsed testis shows little color or none, its flow choked off at the twist. That loss of color is the sign the scan is built around. A flow that is gone on the painful side is the mark of a torsion. The two sides are read together, and this is the rule of the scan. The probe is set on the well testis first, the color turned up until its flow shows clearly, and the same setting carried across to the sore one. The well side gives the measure of a normal flow in that patient, on that machine, at that moment. The sore side is held against it. A testis full of color, beside one with none, tells the story at a glance. The comparison turns a faint or doubtful picture into a clear one, since the eye judges the bad side against a known good. The color is read in the substance of the testis. A ring of flow around a dead testis can fool the eye into calling it alive, so the center is what counts. The vessels sought are the small ones threading the body of the testis, the ones a torsion shuts down. The reading is made slow, the color watched over several beats of the heart, so a flow that comes only in a faint pulse is given its chance to show. The flow answers the question the surgery turns on. A testis with blood still in it can be saved by an untwisting. A testis with no flow has been starved. The longer it has gone, the less there is to save. The scan that shows the flow, or its loss, is the scan that sets the speed of everything that follows. The reading is made with care. The flow in a small testis is faint. A hasty look can miss it, or call it gone when a trace remains. The settings are turned to catch a slow flow, the probe laid with a light touch, both sides read the same way, before the call of present or absent is made.
The signs in gray scale
The plain gray picture carries its own marks of a torsion, read alongside the flow. Early in a torsion the testis can look normal in gray scale, with the loss of flow the only sign. So the flow is read first and trusted. Once its color is gone, even a normal-looking testis is not a well one.
As the hours pass the gray picture changes. The starved testis swells. It darkens, its even texture breaking up in patches. A little fluid gathers around it. The skin of the scrotum thickens. The testis may lie crosswise, turned off its upright line, pulled to a new angle by the twist in its cord.
The twist itself can sometimes be seen. The cord above the testis, traced upward, can show a spiral where it turns on itself, a sign named the whirlpool for its shape. A whirlpool in the cord is a direct mark of the twist. Color laid over it shows the vessels spiralling into the knot. The sign is sought when the cord can be followed cleanly.
The flow can be read as a trace as well as a color. A sample taken in the testis draws a waveform of the blood moving through it, the rise of each heartbeat shown as a wave. A waveform that is flat, or that shows the pulse pushing in and then drawing back out, is the mark of a flow the twist has strangled. The trace adds a measure to the color, of use when the color alone is hard to call.
The gray picture also speaks to the hours gone by. A smooth, even testis, with only the flow missing, has been caught early, in good time for a rescue. The testis darkens and turns patchy only after hours of starving, its tissue breaking down. The look of the testis on the screen lends a rough sense of how far the clock has run.
Settings to catch a faint flow
The flow in a testis is faint. The machine is tuned to bring it out. The scale is turned low, so the Doppler answers to a gentle flow and holds the faint signal on the screen. The filter that hides slow signals is dropped. Power Doppler, which reads the faintest flow, is the setting many reach for in a small or a young testis.
The hand on the probe matters as much as the dial. A heavy press on the scrotum can squeeze the small vessels shut and rub out a flow that is there. The probe is laid with the lightest touch, a pool of gel taking up the weight, so a true flow is not pressed away. A warm room and warm gel keep the scrotum loose, the better to see a faint flow.
The comparison is the safeguard over all of it. The well side, read on the same low scale and the same light touch, proves the machine is set to show the flow that is present. A sore side that stays dark on settings that light up the well side is dark for a reason. Tuning the scan on the good testis is what makes the silence on the bad one mean something.
One view sets both testes side by side in a single picture. The probe is laid across the two at once, with the color on, so the flow of the well side and the sore side show in the same frame. The eye reads the two together, the bright color of one beside the silence of the other. This single picture is among the clearest the scan can give.
The trap of flow that lingers
A flow that is still there does not always clear a testis. A cord twisted part of the way, or twisted and partly loosened, can pinch the veins. Some blood still creeps through the stiffer arteries. The testis then shows a flow that is reduced, or even a flow that looks near normal. The torsion can be underway even then.
This trap sets a firm limit on the scan. A normal flow lowers the chance of a torsion. Some risk remains. Some flow does not clear a boy whose story strongly points to torsion. The picture is weighed with the story. A doubt the story keeps alive is settled in the operating room.
The flow is read for how much there is, not only for whether it is there. A testis with clearly less color than its partner, even with some flow left, points to a torsion that is partial or early. The scan reports what the flow shows and how it sits against the other side. The surgeon, holding the picture and the story together, makes the call to explore.
The degree of the twist sets how much flow is lost. A cord wound a full turn or more strangles the blood altogether. The testis shows no color at all. A cord wound part of a turn pinches the flow part way. A thread of color may still creep through. The amount of color left tracks the tightness of the twist, which is the reason a faint flow is read with care and not taken as a clearance.
A testis can twist and untwist on its own. A boy with bouts of sudden testicular pain that come and pass may have a cord that winds and unwinds on its own. Between the bouts the scan can look normal. The story of a pain that keeps coming back is the clue. A testis that does this is fixed in surgery before a twist holds for good.
The look-alikes
Color Doppler of epididymo-orchitis. The testis and its tube are flooded with red and blue color, a flow run high by the infection. This flooding is the reverse of a torsion. A torsion drains the color away. Image: D’Andrea et al., CC BY 2.5.
A swollen, painful testis has more than one cause. The flow tells them apart. An infection of the testis and its tube, an epididymo-orchitis, floods the part with blood. The Doppler lights up bright over an infected testis. A torsion empties the testis of color. The flow that is gone points to a torsion. The flow that is heightened points to an infection.
A smaller twist has its own look. The little tag of tissue at the top of the testis can twist on its own, a torsion of the appendix testis. The testis itself keeps its normal flow. The pain centers on a tender spot at the top that can show as a dark dot through the skin. The blue tinge of that dead tag, seen through thin skin, gives the sign its name. This is a gentler trouble, settled without surgery as a rule.
Other troubles round out the list. A blow to the scrotum, a hernia slipping down into it, a gathering of fluid or blood all have their own look on the screen. The scan sorts the painful scrotum by the flow and the gray picture together. The one cause that cannot wait is the one it has to catch.
Sorting these is the daily work of the scan. A painful scrotum can come from a twist, an infection, a knock, or a swelling. Each takes a path of its own. Surgery undoes a torsion. Antibiotics and rest settle an infection. The scan that reads the flow and the gray picture points the care down the right road from the start.
When the scan must yield to the knife
Ultrasound serves the diagnosis. The clinician makes it. A torsion is a thing judged by the whole picture, the story and the hand on the scrotum as much as the screen. A scan is one voice in that judgment, a strong one when it is clear, a quiet one when the case already speaks for itself.
The strongest cases skip the scan. A boy whose story and signs cry torsion is taken to surgery without waiting for a picture, since the wait would cost the testis the time it cannot spare. The surgeon explores, untwists, and judges the testis by eye. The scan would only have slowed a path that was already set.
The scan does its real work in the middle ground. A picture that is not plain, a story that could be a torsion or an infection, a testis whose flow is the thing in question, all turn to the scan for the answer. A clear loss of flow sends the patient to surgery. When the flow is full and the story is mild, the search turns to the other causes.
The judgment rests with the surgeon. The scan is one voice among the story, the exam, and the picture. A urologist called to a sore scrotum weighs them as one. A scan that argues against a strong clinical story does not settle the matter. It is weighed in with the rest. The testis is too dear, and the clock too short, to hang the whole call on a single faint signal.
After the diagnosis
The treatment of a torsion is to untwist the cord and fix the testis in place. The surgeon opens the scrotum, turns the testis back, and watches the color return to it. A testis that pinks up is stitched down so it cannot twist again. The other testis is fixed at the same time, since the build that let one twist tends to sit on both sides.
A doctor can sometimes untwist the testis by hand before surgery. The testis is turned outward, toward the thigh, the way a book is opened, to unwind the cord and bring the blood back. A pain that eases and a flow that returns on the scan are signs the turn has helped. This is a holding measure that buys time. The surgery to fix the testis comes next.
The newborn is a case apart. A torsion found at or near birth has often turned before the birth, the testis lost by the time it is seen. Its twist sits outside the lining of the testis, in a place all its own. The scan and the care are weighed for the newborn on their own terms.
A testis too long starved cannot be saved. A testis that stays dark after the untwisting, with no life returning to it, is removed, since dead tissue left behind brings only harm. The hard truth of the clock shows here, that the testes lost are commonly the ones that came late, after the hours of flow had run out.
The aim of the whole effort is to beat that clock. The fast story, the quick scan in the doubtful case, the straight path to surgery in the clear one all serve the single goal of blood brought back to the testis in time. A torsion caught early is a testis kept. A torsion caught late is a testis lost.
The whole case is the clock
Testicular torsion is a race the scan is built to win. A twisted cord cuts the blood to the testis. The gland dies by the hour. Past about six hours the testis is hard to save. A scan that shows the missing flow turns a long wait for a surgeon into a quick call to the operating room. The hours it saves are the testis it saves.
The scan goes to where the patient is. A unit carried to the bedside, or to the emergency room cot, reads the flow in each testis the moment the boy arrives. Color Doppler puts the color of both testes on one screen. The missing flow on the sore side shows at once.
The flow is faint. The settings decide whether it shows. The Doppler box is set small and low. A normal flow does not clear the boy, since an early or partial twist can leave some flow. The sudden, severe pain still rules. A boy with that pain goes to surgery on the picture and the story together.
Common questions about ultrasound for testicular torsion
How does ultrasound diagnose a twisted testis?
By the blood flow. On color or power Doppler a torsed testis shows little flow or none. The other testis, read on the same settings, shows the normal flow for comparison. The plain gray picture can show a swollen, dark testis, a twist in the cord called a whirlpool sign, and fluid around the testis. Early on it can look normal.
How quickly must testicular torsion be treated?
Within hours. A testis untwisted in the first few hours is saved in almost every case. The chance falls steeply after that, and by a full day it is small. This is why a clear case goes straight to surgery, and ultrasound is used only when it does not slow that path.
Can ultrasound rule out testicular torsion?
Not on its own. A partial or early torsion can leave some blood flow in the testis. A normal flow lowers the chance of a torsion. Some risk remains. A boy with a strong story of torsion is explored in the operating room even when some flow is seen.
How is torsion told from an infection on ultrasound?
By the direction of the blood flow. An infection of the testis floods it with flow, so the Doppler lights up bright. A torsion empties the testis of flow, so the color is reduced or gone. The flow that is heightened points to an infection. The flow that is lost points to a torsion.
Why are both testes scanned?
The well testis sets the measure of a normal flow in that patient, on that machine, at that moment. The sore testis is read against it on the same settings. A testis lit with color, beside one that stays dark, shows the torsion clearly. A single side read alone might leave a doubt.
Can torsion untwist on its own?
Yes. An intermittent torsion untwists on its own. The pain eases as it does. It can twist again and stay twisted the next time. A boy whose pain keeps returning is sent to a urologist, since one of those twists may not let go.
About the Author
Julien Mercier
Senior R&D Engineer · Medical Ultrasound Transducer Development
Senior R&D Engineer with an M.S. in Applied Physics and over 15 years of experience in medical ultrasound transducer development, specializing in the design verification and performance testing of high-frequency imaging transducers. Currently leading the development and verification of the company’s next-generation high-frequency linear-array transducer, responsible for imaging performance evaluation and reliability analysis in preclinical testing. Brings extensive hands-on experience in piezoelectric element tuning, beamforming parameter optimization, and system-level performance testing.
