Abstract
This pictorial review explores the wide spectrum of paediatric groin and scrotal masses. Examples overlap with the adult population but concentrate on those more common in, or unique to, children. Correlation with other imaging modalities is included where appropriate.
Keywords
Introduction
Ultrasound is an excellent modality for the initial assessment of superficial groin lesions in the paediatric population. It is quick, non-invasive, with no radiation dose or requirement for general anaesthetic. Interaction with child and carer allows the operator to gain a detailed history, provide reassurance and alleviate anxiety. Our department is receiving an increasing number of requests, from paediatricians and GPs, for evaluation of paediatric groin and scrotal lumps and bumps.
The purpose of this pictorial essay is to raise awareness of the wide spectrum of lesions encountered in children. Examples overlap with the adult population but concentrate on those more common in, or unique to, children. Correlation with other imaging modalities is included where appropriate.
Embryology
A little knowledge of the embryological development of the groin, particularly in males, can help understand the common causes of groin and scrotal lumps and bumps. Knowledge of two embryological structures, the gubernaculum and processus vaginalis peritonei, can help explain the clinical diagnoses.
Normal testicles develop within the abdomen and descend into the scrotum with two distinct phases: transabdominal (8–15 weeks) and inguinoscrotal (25–35 weeks). 1 This complex process is due to the hormonally controlled migration of the gubernaculum, which attaches the caudal pole of the testicle to the scrotum (in females the ovary to the labium majus).
The processus vaginalis peritonei is an evagination of the peritoneum into the scrotum. It lies anterior to the gubernaculum.2,3 Three steps occur in the normal obliteration of the processus vaginalis: (a) closure of the deep inguinal ring, (b) closure of the area just above the testis and (c) atresia of the processus vaginalis between the two constrictions (the funicular process). 4 These steps lead to formation of the potential cavity of the tunica vaginalis, a mesothelium-lined sac composed of a visceral layer and a parietal layer. The visceral layer envelops all but the posterior aspect of the testis, and the parietal layer lies against the scrotal wall. 2
Pathology
Congenital cryptorchidism (undescended testis)
This is failure of the normal descent of the testes from the abdomen into the scrotum. The affected testicle can be found anywhere along the descent path. It is an important diagnosis to make as it is linked to impaired fertility (33% in unilateral cases and 66% in bilateral undescended testes) and a cancer risk 5–10 times greater than normal is observed over time.
5
The mainstay of therapy for undescended testes is operative treatment within the first two years of life in order to avoid ongoing testicular degenerative changes. The surgical therapy for the palpable undescended testis is orchiopexy (the undescended testis is fastened inside the scrotum) and when the testis is non-palpable, a supplementary laparoscopic approach is used (Figures 1(a)–(c)).
6
Undescended testis. Images (b) and (c) show solid, oval, hypoechoic masses orientated along the inguinal canal, and palpable in the groin. No corresponding scrotal testis felt. They are smaller and of lower echogenicity than a normally sited testis (Image a). It is important to assess vascularity
Patent processus, inguinoscrotal hernias, communicating hydroceles and spermatic cord hydroceles
The processus vaginalis remains patent at birth in 1 in 5 as a potential space. A persistent processus vaginalis is often asymptomatic and closes during the 1st year of life, probably in response to the surge in serum testosterone that normally occurs at 1–2 months of age.
2
It is the potential space that enlarges to form either an inguinoscrotal hernia, which contains bowel or omentum, or a fluid-containing hydrocele. The differentiation between these can be made by the ultrasound appearances. A communicating hydrocele is anechoic with posterior acoustic enhancement and no vascularity. Both bowel and omental hernias will demonstrate vascularity whilst bowel will be tubular, air- or fluid-filled structures, which demonstrate peristalsis and omentum is hyperechoic. Spermatic cord hydroceles are rarer entities seen in less than 1% of cases.
7
They differ from communicating hydroceles as they represent a loculated fluid collection along the spermatic cord, separated from and located above the testicle and the epididymis.
4
Two types are described; these are the encysted hydrocele of the cord, where the fluid collection does not communicate with the peritoneum or the tunica vaginalis, and the funicular hydrocele (FH), where there is a fluid collection along the cord, communicating with the peritoneum at the internal ring (Figures 2(a)–(d) and 3).
7
Images (a) and (c) show examples of patent processus vaginalis (thick arrows). These fluid-filled sacs extend from the abdominal cavity through the inguinal canal into the scrotum. Image (b) shows a traditional hydrocele of the scrotum bathing the gonad. Image (d) is an encysted hydrocoele of the cord, palpable and static in the groin with no communication to peritoneum or scrotum Inguinal hernia TS (left) and LS (right) images of the inguinal canal show fatty tissue entering the canal and extending down towards the scrotum. The amount of soft-tissue increased during valsalva (crying)
Testicular torsion
It can affect any age group but has a bimodal distribution occurring soon after birth and more commonly at puberty. 8 The two age groups have anatomically different torsions. In neonates it is usually an extravaginal torsion, where the complete spermatic cord with all its contributing structures (vas, vessels, processus vaginalis and investing fascias) is thought to undergo torsion. 9 The exact mechanism of injury is uncertain but felt to be due to the increased mobility of the tissues during birth. 10 In adolescents and older age groups, an intravaginal torsion occurs where only the testis is involved. The bell clapper deformity is the most common predisposing factor to intravaginal torsion and is due to an abnormal insertion of the tunica vaginalis allowing the testis wide mobility. 11 It occurs when the visceral tunica vaginalis extends completely around the testicle and epididymis to envelop a length of the spermatic cord. 12
Testicular torsion (Figure 5) is a time-critical emergency, and most suspected cases are taken straight to surgery without any imaging. Imaging may delay surgery to restore blood supply, with the testis usually being unsalvageable after 6 hours. 13
Imaging is required when there is uncertainty regarding the diagnosis. The clinical mimic is epididymo-orchitis (Figure 4), which is inflammation of the epididymis and testicle secondary to either a urinary or sexually transmitted infection.
US Testes: Increased vascularity in epididymo-orchitis
Reduced blood flow on colour and pulsed Doppler is expected in the affected testicle in torsion whilst hyperaemia will be seen in epididymo-orchitis. However, a normal scan can be seen in cases of intermittent torsion and so a normal ultrasound does not rule out torsion.
One-day-old baby boy. Left scrotal swelling noted at infant check. No distress. Ultrasound: extravaginal torsion; the left testis is enlarged and of mixed appearance and echotexture with large areas of reduced echogenicity. Enlarged left epididymis but normal echotexture
Vulval lipoma
Lipomas are fat-containing mesenchymal tumours that are seen in all age groups but commonly in older groups. Retrospective studies have shown ultrasound of lipomas demonstrates low accuracy and poor intraobserver reliability.
14
On ultrasound, lesions can be hyper/iso or hypo-echoic (Figure 6).
Vulval lipoma US: LS (a) and TS (b) images of a well-defined mass slightly hyperechoic with respect to adjacent tissue. The lesion contains short thin linear striations that run parallel to the skin as does the long axis of the mass. No internal vascularity
Myositis ossificans
Myositis ossificans is benign heterotopic bone formation commonly related to trauma. It is most common in adolescents and young adults and the most common locations are the quadriceps muscles of the thigh and the brachialis muscles of the arm.
15
Ultrasound can be used for early detection. In the earliest stages, a soft tissue mass without calcification is seen. When calcification develops, peripheral
15
and lamellar
16
calcification are more specific for myositis ossificans (Figure 7).
Myositis ossificans. Teenage boy presented with hard lump in upper thigh. US shows acoustic shadowing behind linear hyperechoic area XR shows high (bone density) within the muscle with normal femur adjacent
Lymph nodes and Lymphadenopathy
Superficial lymph nodes are commonly palpable in young children and likely to be seen in ultrasound of the groin. The majority will be normal or benign reactive lymphadenopathy. There are sonographic features which help differentiate between benign and malignant lesions, as in the table below (Figure 8).
17
–
19
The Doppler image shows a reactive node with a normal fatty hilum and increased vascularity. The upper two images show cavitating nodes in acute infection. The bottom right image shows an abnormal node in cat scratch fever
Hip effusion with/without osteomyelitis
Usually a child will present with a limp and usually have hip specific imaging, however, it is a cause of referred pain and should be thought of when imaging the groin if the child has an antalgic gait not mentioned by the referrer (Figure 9).
Osteomyelitis with hip effusion 18-month-old with a 2-day history of not weightbearing on his right leg. US (a) shows a right hip effusion with minor synovial thickening and increased synovial vascularity. A few scattered internal echoes seen within the fluid. XR Right femoral capital epiphysis (b) looks more osteopaenic and there is a lucency extending in from its articular surface. MR A STIR (c) high signal lesion visible in the right femoral epiphysis. This is bounded by the epiphyseal plate. There is minor enhancement and oedema visible in the proximal femoral metaphysis. There is a joint effusion and synovial enhancement following contrast. US Hip effusion (d) showing underlying femur, epiphysis, growth plate, metaphysis and diaphysis
Abscess
An abscess will usually be swollen, tender, erythematous and in the inguinal region causes include incarcerated inguinal hernia, perforated Amyand hernia Abscess, anechoic or hypoechoic with irregular borders, variable internal echoes and through transmission. Surrounding tissues may show inflammatory change, increased vascularity and skin thickening
Conclusion
There is a time-effective triage element to ultrasonic assessment of these lumps and bumps. The dynamic scan allows one to ascertain the presence of a lesion, its location and morphological characteristics. The sonographer is well-placed to guide the referrer towards the most appropriate future management of the patient, be it reassurance from the GP, more complex imaging investigations, referral for surgical opinion or evaluation by a paediatric soft tissue sarcoma centre.
Footnotes
ACKNOWLEDGEMENTS
We are grateful to all of the sonographers and radiologists from York Teaching Hospital, for performing the radiology examinations in this study.