Testicular torsion represents a common surgical emergency. Therefore, early diagnosis and prompt surgical treatment are pivotal.There are two types of testicular torsion, the intravaginal and the extravaginal [1]. The age distribution in pediatric patients has a bimodal pattern: the extravaginal one occuring from the prenatal or perinatal period to the first year of life and the intravaginal one affecting boys older than 12 years old [1]. The most frequent type is the intravaginal one, where spermatic cord torsion is located within the tunica vaginalis [2]. Intravaginal torsion is attributed to bell clapper deformity of tunica vaginalis, which is usually present bilaterally [1, 2].

Fig 1: Illustration of a normal testicle and bell clapper deformity (Dimitra Boviatsi). a. Normal anatomy of the testis. b. Bell clapper deformity is an anatomical variation which pertains to the complete envelopment of the epididymis, distal spermatic cord and testis by the internal lamina of tunica vaginalis, rather than its attachment only to the posterolateral aspect of the testis, as in Figure 1a. Lilac: testis, Red: epididymis, Mauve: spermatic cord, Blue: tunica vaginalis

Generally, the degree of spermatic cord torsion varies from 90° to 1080° [3]. Regarding the degree of torsion, complete, partial, or intermittent testicular torsion can arise. 

• Complete torsion is defined as a degree of spermatic cord twist of 360° or greater, which commonly causes abruption of intratesticular blood flow [1].
• Partial torsion occurs when the affected testis rotates less than 360°; hence, the perfusion of testicular parenchyma is usually preserved [1].
• Intermittent torsion or Torsion-detorsion syndrome refers to recurrent episodes of acute testicular pain followed by spontaneous resolution due to detorsion [4].

The degree of spermatic cord twist is critical for testicular viability, as a tight 720° torsion can lead to necrosis in a four-hour interval [1].  However, in cases of partial or intermittent torsion a twisted testis can be viable after several days [1].

Testicular torsion mainly presents with sudden unilateral testicular pain, sometimes along with nausea, low-grade fever [1, 4]. In cases of partial torsion, the clinical presentation is often atypical with subtle symptoms, whereas in intermittent torsion spontaneous regression of symptoms is noted [2]. Physical exam reveals asymmetric scrotum enlargement with a swollen, tender, erythematous hemi-scrotum [3]. A high-riding testicle or horizontal testicular lie can be also present [3, 4]. Absence of the cremasteric reflex is the most sensitive clinical sign [5, 6]. Negative Prehn’s sign is also noted (when elevating the testes, pain does not resolve) [3]. 

Clinical manifestations of this entity are often nonspecific; thus, an ultrasound exam allows the Paediatric Radiologist to safely narrow down the differential diagnosis of acute scrotum.