Background

Splenogonadal fusion (SGF) is a rare benign congenital malformation in which the spleen is aberrantly connected to the gonads or rarely to the mesonephric derivatives such as vas deferens or epididymis [1, 2]. SGF usually presents as a left-sided scrotal swelling/ mass or cryptorchidism and is frequently misdiagnosed as testicular or epididymal tumours [2]. It is a great clinical masquerader, and accurate preoperative diagnosis is often difficult due to the rarity of this entity. Many patients tend to undergo unnecessary surgical explorations and also orchiectomy. Ultrasonography (USG) is often the first-line imaging modality for the evaluation of a scrotal mass. Colour Doppler combined with ultrasound elastography can provide a valuable clue for the diagnosis. Cross-sectional imaging modalities like magnetic resonance imaging (MRI) or computed tomography (CT) further ascertain the diagnosis [3, 4]. We report a histopathologically proven case of SGF in an adolescent boy presented with scrotal swelling and intermittent pain. We reviewed all the cases of SGF reported in the literature in the last 10 years between 2013 and 2022 with an emphasis on diverse clinical presentations and radiologic findings.

Case presentation

A 12-year-old boy presented with progressive discomfort and swelling in the left scrotum for the last 8 months with associated lower abdominal pain radiating to the left testicle. At the onset, there was a transient symptomatic improvement with conservative management, however, the symptoms gradually worsened over the months with no relief from analgesics. The patient had no history of any urinary complaints or genitourinary trauma. Clinical examination revealed two discrete palpable masses in the left hemiscrotum, one almost indiscernible from the left testis and another near the head of the left epididymis. Both the testes could be palpated in the scrotal sac. No signs of scrotal inflammation were noted.

He was referred to our department for an ultrasound evaluation. The grey-scale ultrasound showed two to three well-defined lobulated oval hypoechoic (as compared to normal testis) solid masses in the upper pole of the left testis, with the largest one measuring approximately 35 × 15 × 13 mm3. On colour Doppler ultrasound, the mass lesions demonstrated higher vascularity in a radiating pattern compared to the normal testis. Strain elastography revealed higher stiffness in the solid mass lesions compared to the normal testicular tissue (Fig. 1). In consideration of the high stiffness and internal branching vascular pattern, the possibility of SGF was raised, and the patient was kept on follow-up to rule out the malignant testicular neoplastic lesion. A repeat ultrasound was performed after 2 months, which showed no interval increase in the lesion size. The patient underwent MR imaging before proceeding with surgical management. This revealed well-circumscribed soft tissue lesions in relation to the upper pole of the left testis. The lesions appear isointense on T1W images, and hypointense on T2W images (as compared to normal testicular parenchyma) with homogenous post-contrast enhancement typically more than the normal testis. Some degree of restricted diffusion was appreciated in the lesions (Fig. 2). No obvious soft tissue strand was noted extending from the lesion into the pelvic and abdominal cavities. With these clinical pictures and imaging morphology, we prospectively put a high possibility of ectopic splenic tissue in the scrotum as a rare syndrome of discontinuous-type SGF. However, a remote possibility of benign tumour of epididymis was given as differential.

Fig. 1
figure 1

A 12-year-old boy presented with progressive swelling in the left scrotum for the last 8 months with associated lower abdominal pain radiating to the left testicle. Sonographic images of the left scrotal region show a well-defined lobulated hypoechoic (as compared to testicular parenchyma) solid lesion (white asterisk in A) in the upper pole of the left testis with intense vascularity on colour Doppler map (in C) as compared to normal testicular vascularity (in B). Shear wave elastography map (D) demonstrates higher elastic modulus in the mass as compared to adjacent testicular tissue (as blue map–harder tissue)

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Fig. 2
figure 2

T2W fat-saturated (A), T1W fat-saturated (B), and post-contrast T1W fat-saturated (C) axial magnetic resonance images reveal two to three (one enlarged) well-defined T2 hypointense (as compared to normal testis) lesions with homogenous enhancement on post contrast study (white arrow), typically more than the adjacent testicular tissue. Coronal (D) and sagittal (E) T2W images demonstrate the orientation of the lesion (black arrow) in relation to the upper pole of the left testis. The area of restricted diffusion is noted in the lesion (asterisk)—high signal on diffusion-weighted image (F) and signal drop in ADC map (G)

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Consequently, surgical exploration was done by a left-sided inguinal incision. Intraoperatively, three dark red, firm, fleshy lesions were identified. The first lesion was within the testicular parenchyma and was connected to two other lesions by a fibrous cord present in the inguinal canal, which terminated distal to the deep inguinal ring. All three lesions were encapsulated by thin white fibrous tissue. These three masses were removed completely with surgical margin clearance, and most of the left testis was preserved (Fig. 3). The post-operative period was uneventful. Histopathological examination of the resected mass lesions revealed a peripheral capsule with multiple cortico-medullary differentiation with white and red pulp. This was consistent with ectopic splenic tissue with no evidence of malignancy. Testicular seminiferous tubules were noted adjacent to the lesions (Fig. 3).

Fig. 3
figure 3

Intraoperative surgical exploration image (A) confirms the radiologic findings. Gross resected specimen image (B) and cut section pathological image (C) show nutmeg appearance of sectional splenic tissue (red asterisk) and testicular tissue (black asterisk). Low (D)- and high (E)-power microscopic views of histopathological images demonstrate splenic tissue (red asterisk) and testicular tissue (black asterisk) in the lesion and confirm the diagnosis of splenogonadal fusion

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Multiple methods were used to find the current research publications on splenogonadal fusion. We started by searching the Scopus, PubMed, and Google Scholar databases online since 2013 with the combination of key terms including 'splenogonadal fusion', 'cryptorchidism', 'accessory spleen', 'scrotal swelling', and 'orchiectomy'. This search strategy recognized the abstracts of published articles, while other research articles were discovered manually from the citations. The initial search returned 427 records from all the databases from where 382 articles were found after removing duplicates. The search results were confined to journal articles written in English. We first reviewed the titles and abstracts for each of the 382 articles to determine their relevance. Following the criteria set out above, 289 studies were eliminated, and 93 studies were retained. These studies were then evaluated by going through the whole article. At least three authors independently reviewed each abstract. Minor disagreements were addressed in a meeting that resulted in an agreement, and finally, 63 articles were retained. The manuscript was drafted based on these final articles. Google spreadsheet was used to capture the data from different studies, and Microsoft Excel spreadsheet was used to tabulate the findings. One of the most comprehensive reviews of this rare entity in the recent literature was that of 61 cases by Malik et al. in 2013 [5]. Since then, from 2013 there were 62 articles with a total of 67 cases reported in the scientific literature till December 2022. We performed a comprehensive review of the literature on these reported cases of SGF in the last 10 years and summarized the details in Table 1 [3, 4, 6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65].

Table 1 Details of the reported cases of SGF from 2013 till December 2022
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Results

Out of the 67 cases analysed, only one of them was female, while the rest were males. (Table 1). A considerable proportion of patients (71.2%) were observed to be below the age of 20 years (Table 2). The most prevalent clinical presentation among these cases was cryptorchidism, accounting for 28% of the occurrences, followed by painless scrotal swelling, which constituted 23.5% of the cases (Table 3). In terms of the types of SGF observed, the discontinuous type was found to be more prevalent, accounting for 64% of the cases, while the continuous type represented ~ 36% of the cases. Regarding the management approach, orchiectomy, which includes one case of partial orchiectomy, was conducted in 36% of the total cases.

Table 2 Age at the time of diagnosis in reported cases of SGF
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Table 3 Presenting clinical symptoms in reported cases of SGF
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Discussion

SGF is a rare congenital malformation first observed by German pathologist Bostroem in 1883. This can be associated with other congenital anomalies, such as cleft palate, cardiac defects, and micrognathia [2, 5]. Splenogonadal fusion was first categorized by Putschar and Manion in the year 1956 into two types, the continuous and the discontinuous form. The continuous form was reported to be slightly more common (58%) than the discontinuous type according to the previously reviewed literature [5]. However, in our 67 reviewed cases, only 24 cases (36%) have a continuous type. In the continuous type of SGF, a cord-like structure attaches the orthotropic spleen to the gonad. This cord-like structure can be fibrous, entirely splenic, or can have a beaded appearance containing intervening fibrous and splenic nodules similar to a 'rosary bead' [20]. The discontinuous type of SGF usually presents as a firm scrotal mass, and no connection between the spleen and the ectopic splenic tissue can be established and is considered a special variant of accessory spleen. In this type, the ectopic splenic tissue is adherent to the testis or rarely other mesonephric derivatives like the epididymis. Most cases of continuous-type SGF have been associated with syndromic congenital anomalies, and the cases of discontinuous-type SGF have been associated with isolated inguinal swellings [6, 41].

The exact aetiology remains uncertain, however, numerous theories have been proposed to explain its etiopathogenesis and association with other malformations. If there is inflammation of the peritoneal surfaces adjacent to the spleen and gonadal ridges during the development process, resulting in adhesion, this can initiate the fusion of the two organs before their descent. Between the 5th and 8th gestational weeks, the developing splenic tissue becomes fused to the gonad and is subsequently pulled caudally with the descent of the gonad into the pelvis during the 8th to 10th weeks of gestation. It is hypothesized that a teratogenic event occurring during the aforementioned gestational period causes limb deformities, micrognathia, and other congenital anomalies in addition to SGF [8, 11, 32, 57].

Although SGF can occur in both sexes, it is predominantly symptomatic in males. This disparity is mainly due to the superficial location of the testis, which allows for readily frequent palpation and detection vis a vis the abdominal location of ovaries in females. SGF is commonly diagnosed in females as an incidental finding during surgery for a different diagnosis or on autopsy [5, 41]. It is typically noted on the left side in up to 97% of cases [5]. Even in our review as well, all cases were males with SGF on the left side with the exception of only one case presented on the right as reported by Marwah et al. [37]. Guzman et al. [64] reported a case of symptomatic SGF with splenic torsion in an adolescent female who underwent operative detorsion and partial splenectomy. SGF mostly presents before 20 years of age, with a reported value of 68% in the review done by Malik et al. [5]. In our review as well, 47 out of 67 cases (71.2%) presented below 20 years of age. Clinical presentation varies from simple inguino-scrotal swelling to strangulated inguinal hernia. Varied clinical presentations are tabulated in Table 3. A wide variety of clinical presentations makes it a great clinical masquerader. Cryptorchidism was the most common presentation (28%) in our reviewed cases, followed by painless scrotal swelling (23.5%).

SGF is mostly a retrospective diagnosis based on histological features of a surgical or autopsy specimen, and the radiologic literature is limited. This stresses the need for a high index of suspicion and awareness for a potential SGF preventing unnecessary orchiectomies. Previously before the era of cross-sectional imaging and sonography, technetium-99m sulphur colloid scan was the only diagnostic clue towards a diagnosis of SGF [5, 29]. A definitive diagnosis of SGF may not be made solely based on sonographic findings. However, a well-defined lobulated capsulated homogenous hypoechoic mass close to the testis with a branching/ radiating vascular pattern resembling the vascular pattern of normal splenic tissue in a patient with left-sided scrotal swelling along with normal tumour markers for testicular malignancies should raise the suspicion for SGF. A disorganized branching criss-cross vascular pattern from the testicular mass lesion on colour Doppler may indicate testicular malignancy [66]. Microflow imaging (MFI) is a recently developed ultrasound technique by Philips (Bothell, WA, USA, a similar technique known as superb microvascular imaging [SMI]; Toshiba Medical Systems, Tokyo, Japan) different than conventional power Doppler technique, which is very sensitive for detecting slow and weak blood flow from tissue with high spatial resolution [67]. In MFI, the artefact reduction technique is applied to separate slow flow signals from tissue motion artefacts without the use of contrast agents. Studies on the utility of MFI in breast, thyroid, testicular, and hepatic lesions are available. However, to the best of our knowledge, no literature on the application of MFI in SGF is available. This technique may be useful in detecting the pattern of tissue vascularity in SGF and testicular tumours. With the advent of ultrasound elastography, testicular tissue can be distinctly differentiated from other tissue like the spleen having higher stiffness [3, 21]. Contrast-enhanced ultrasonography (CEUS) can facilitate the evaluation process as the ectopic splenic tissue shows avid atrial phase enhancement. In the continuous type of SGF, computed tomography (CT) can demonstrate the connection with the spleen and delineate vasculature originating from the splenic hilum [25]. MR evaluation of the pelvis and abdomen helps better delineation of SGF, which can differentiate between continuous from discontinuous types owing to the better soft tissue spatial resolution. Signal intensities and enhancement patterns of the ectopic splenic tissue in SGF will be similar to the normal orthotopic splenic tissue. MR imaging is also useful to differentiate SGF from other malignancies as ectopic tissue usually adheres to testicular tissue with maintained fat planes. Among our 67 reviewed cases, many cases do not have any radiologic data, and MR imaging is available in less than 10 cases [3, 7, 9, 17, 19, 51, 56, 58, 63]. Hence, we emphasize using radiological modalities in the diagnostic evaluation of this entity and their accurate interpretation for correct clinical guidance and management.

Tissue diagnosis is the gold standard in establishing the diagnosis of this entity. The ectopic splenic tissue in SGF shows the normal splenic architecture on histopathology and demonstrates capsule, cortex, and medulla with red pulp and white pulp with sinusoids. Ectopic splenic tissue may sometimes show thrombosis, calcification, fat degradations, and hemosiderin depositions. Few cases had been reported with an intermingling of splenic and gonadal tissue histologically [2, 5]

Unnecessary interventions can be avoided if a confident diagnosis using ultrasound and cross-sectional imaging modalities is made. A testis-preserving surgical procedure should be planned in a patient with SGF if however, performed [5, 41, 51, 57]. There are few cases in the literature reporting an association between SGF and testicular malignancy [64]. SGF associated with cryptorchidism increases the risk of malignancy and hence orchiectomy is a better option [41]. A complete orchiectomy is often not required because the fused splenic tissue can be dissected safely off the tunica albuginea. Even if SGF is almost always a benign condition, the cord attached to the ectopic splenic tissue is liable to undergo torsion as well as associated with congenital hernias as described in a few case reports [3, 7]. Orchiectomy was done in 24 cases out of 67 male patients (36%) in our review, and it was about 37% and 24% in the cases reviewed by Carragher [1] and Malik et al. [5], respectively. The symptomatic adolescent female reported by Guzman et al. [64] underwent laparoscopic detorsion and partial splenectomy with preservation of the left ovary.

Conclusions

Splenogondal fusion is an uncommon differential diagnosis in patients with scrotal swelling. Its typical imaging findings should raise suspicion. We suggest that the addition of colour Doppler and elastography to routine grey-scale ultrasound can increase diagnostic confidence. Subsequent cross-sectional imaging with MR helps categorize the subtype and pre-operative planning. In our case, unnecessary radical orchiectomy was avoided as a differential diagnosis of SGF was prospectively suggested based on imaging findings. Knowledge of this entity along with familiarization with its imaging features among radiologists is essential for surgical prognostication and avoiding unnecessary orchiectomy.