Testicular Tumors

Here is a slightly uncomfortable truth I wish someone had handed me on day one: the scariest masses in the body are often the ones that don't hurt. A testicular tumor classically shows up as a painless lump a young man found in the shower and ignored for a while because it didn't bother him. That's exactly the problem. Pain gets people to the doctor; silence buys the tumor time.

The good news is that ultrasound is almost embarrassingly good at this. Point a probe at a scrotum and you can usually answer the only question that matters before the gel has warmed up.

The one question: inside or outside the testis?

Imagine the testis as an egg, and the rest of the scrotum as the padded box it ships in. Lumps that grow inside the egg (intratesticular) are guilty until proven innocent — the strong majority of solid intratesticular masses in an adult are malignant. Lumps that grow in the box around the egg (extratesticular) — along the epididymis, the cord, the surrounding tissue — are overwhelmingly benign. Same scrotum, wildly different stakes, and the dividing line is the thin bright capsule of the testis itself, the tunica albuginea.

So the radiologist's whole opening move is geographic: which side of the eggshell is this thing on?

Findings by modality

Ultrasound

Use a high-frequency linear probe, scan both testes in the same frame for comparison, and remember what normal looks like: an adult testis is roughly 5 × 3 × 2 cm with a uniform, medium-gray, salt-and-pepper echotexture that regresses a little with age. The mediastinum testis — the bright linear band running along the back where the tubules converge — is normal and gets mistaken for a lesion by everyone exactly once.

A classic tumor is a solid mass within the testis that is usually hypoechoic — darker than the surrounding parenchyma. It distorts the architecture, and on color Doppler it often lights up with internal blood flow, because tumors are greedy and build their own plumbing. Bigger tumors can replace most of the testis, at which point the only clue that this used to be a testis is a crescent of normal tissue at one edge.

A few practical tells:

• Solid vs. cystic matters enormously. A purely simple cyst (anechoic, thin-walled, bright through-transmission) is reassuring. A solid, vascular nodule is not.
• Seminomas tend to look fairly uniform — a homogeneous, well-defined hypoechoic blob, sometimes lobulated, usually without calcification or cysts.
• Non-seminomatous germ cell tumors (embryonal carcinoma, yolk sac tumor, choriocarcinoma, teratoma, and the mixed tumors that combine them) tend to be the messy ones — heterogeneous, with cysts, calcification, and hemorrhage all mixed together like a poorly stirred trail mix, and often a less defined edge.
• Lymphoma and metastases go on the list in older men: often bilateral, often diffusely infiltrating rather than a discrete lump, and very vascular.
• Sex cord-stromal tumors (Leydig cell, Sertoli cell) are the small, usually benign ones that look just like small germ cell tumors. Ultrasound can't reliably separate them, which is why the pathologist still has a job.

But here's the honest caveat, and it's important: you do not name the exact tumor type from the ultrasound. The picture tells you there is a worrisome solid intratesticular mass. The pathologist, with a hand from the serum tumor markers (alpha-fetoprotein, beta-hCG, and LDH), tells you what it is.

Figure · US

Testicular microlithiasis deserves its own paragraph. These are tiny, non-shadowing bright specks scattered through the testis like someone shook pepper inside the egg. On its own it's not cancer, and most men with it never develop a tumor — but it travels in the same crowd as germ cell tumors, so it changes the plan depending on who's carrying it (see "The numbers" below).

Figure · US

CT

CT does not diagnose the testicular mass — ultrasound already did that — but it stages it. Germ cell tumors spread first along the lymphatics that follow the gonadal vessels up to the retroperitoneal nodes around the renal hilum and aorta, not to the groin (unless the scrotum has been operated on or the tumor has invaded the scrotal skin). So the staging CT of the chest, abdomen, and pelvis is looking for retroperitoneal nodal enlargement, then lung nodules, then liver and other distant sites. The nodal size cutoffs and TNM stage definitions belong to the staging manual, and this page deliberately doesn't quote them.

MRI

Scrotal MRI is a problem-solver, not a screening tool. It earns its keep when ultrasound is equivocal about whether a lesion is intra- or extratesticular, when a lesion could be a segmental infarct or hematoma rather than a tumor, or when the surgeon is weighing testis-sparing surgery for a small lesion. Tumors are typically low signal on T2-weighted images against the bright normal testis and enhance with contrast; a bland infarct or an old hematoma doesn't.

The traps that look like tumors (and the tumor that hides)

Plenty of benign things impersonate cancer, and a couple of cancers play hard to find.

And the sneaky one: a tumor can occasionally "burn out," leaving mostly scar and calcification in the testis while it has already spread elsewhere. So a man with a retroperitoneal mass and a suspiciously shrunken, calcified testis deserves a hard second look — the primary may be a small scar you would otherwise have ignored.

What imaging does — and stubbornly does not — do

Let me draw the lane markers, because mixing these up is the most common conceptual mistake.

Notice what's missing: you almost never biopsy a suspicious testis through the scrotum, because of the worry about spreading tumor along the needle track and seeding a new lymphatic territory (the scrotal skin drains to the groin, and the testis doesn't). The testis comes out whole, through the groin. Imaging's role is to ring the alarm and then map the spread — not to take a tissue sample.

The numbers

Most of what a resident wants here — marker cutoffs, stage groupings, node-size thresholds — belongs to the staging manual and the oncology team, and I've kept it off this page rather than half-remember it. What I will give you is the normal testis and the microlithiasis follow-up rule, which is the one number-shaped decision the reporting radiologist actually owns.

The microlithiasis rule is the ESUR scrotal imaging subcommittee's guidance, and it's worth memorizing because it's the one place a scrotal ultrasound report is expected to recommend something rather than just describe.

How good is the test

There is no robust pooled sensitivity or specificity figure to quote for ultrasound detection of a testicular tumor. In practice ultrasound is treated as close to definitive for the presence of a solid intratesticular mass — the working assumption is that a palpable testicular lump plus a normal ultrasound is reassuring, and a solid vascular intratesticular mass goes to the urologist regardless of what else the scan shows. What ultrasound cannot do with any reliability is tell seminoma from non-seminoma, or a small benign stromal tumor from a small germ cell tumor; the histological type is a pathology call.

Mimics

Reporting

What the urologist needs from the ultrasound report:

• Location: intratesticular or extratesticular, stated explicitly, and which testis.
• Size in three planes and the size of the normal testicular tissue that remains — that last bit matters if testis-sparing surgery is on the table.
• Character: solid, cystic, or mixed; echogenicity; calcification; internal vascularity on color Doppler.
• The other testis: normal, or also involved, with or without microlithiasis.
• Microlithiasis if present, on either side, with the follow-up recommendation appropriate to the patient's risk factors.
• Extras: hydrocele, varicocele, epididymal involvement, and the clinical question you're answering.
• The next step, stated: "Solid intratesticular mass; urgent urology referral recommended" — with the reminder that serum tumor markers and staging CT are the oncology team's next moves.

The one thing to remember

If a young man has a painless solid lump inside the testis on ultrasound, you treat it as cancer and get him to the right people fast. Not pain, not size, not your gut — the location and the solid texture are what matter. And if the lump is throbbing and tender instead, that's a different page entirely: the don't-miss emergency is testicular torsion, where the clock, not the biopsy, is what you're racing.

References

• Lam Shin Cheung J, Bhaduri M. A sound approach to stay on the ball—a review of scrotal pathologies on ultrasound imaging. Br J Radiol 2026;99(1181):847–858. Used for: the normal adult testis of about 5 × 3 × 2 cm, homogeneously echogenic and regressing with age, in "Findings by modality" and "The numbers."
• Richenberg J, Belfield J, Ramchandani P, et al. Testicular microlithiasis imaging and follow-up: guidelines of the ESUR scrotal imaging subcommittee. Eur Radiol 2015;25(2):323–330. Used for: the microlithiasis follow-up rule in Key Points, "The numbers," and "Reporting": no follow-up for isolated microlithiasis without risk factors; annual ultrasound up to age 55 when risk factors are present (personal or family history of germ cell tumor, maldescent, orchidopexy, testicular atrophy); urgent specialist referral for microlithiasis with a testicular mass.