Intrascrotal Lipoblastoma Case Study: A Rare Cause of Paratesticular Mass in a Pediatric Patient

Background

The differential diagnosis of a scrotal mass in a pre-pubertal child is broad and includes both malignant causes, such as paratesticular rhabdomyosarcoma and germ cell tumors; and benign etiologies, like supernumerary testis, epididymitis and testicular or epididymal appendage torsion. Lipoblastomas are rare benign neoplasms originating from primitive white fat cells that are typically fast growing and occur predominantly in young children, with 90% presenting prior to three years of age. They are more common in males than females and are found most frequently on the trunk or extremities. However, they can involve many sites including retroperitoneum, head and neck, mediastinum and visceral organs. They can, in rare cases, be paratesticular in location.¹ Here we present an unusual cause of lipoblastoma presenting as a paratesticular mass in a pediatric patient.

Diagnostic findings

An 18-month male presented to urology clinic with concern for left polyorchidism. His pediatrician had palpated a possible extra left testicle on exam three months prior, prompting a referral to urology. His mother reported no change in size since initially noted, nor any signs or symptoms concerning for hernia or communicating hydrocele. A scrotal ultrasound at the time of initial diagnosis showed a 1.5 cm spherical structure abutting the left testis which appeared solid in nature. This was felt to be possibly a supernumerary left testis though malignancy could not be excluded. 

Exam at the time of presentation to urology clinic revealed a firm, round mass distinct from the left testis which was palpable in the upper left hemiscrotum (Figure 1). This was non-tender, and there were no right side abnormalities noted. A repeat scrotal ultrasound was performed showing a homogenous, mildly hyperechoic mass with arterial and venous blood flow adjacent to the left testis now 1.9 x 1.5 x 1.8 cm (Figure 2). Given the increase in size with vascularity over a three-month period, there was concern for malignancy and a left inguinal exploration with partial versus radical orchiectomy was planned. Pre-operative blood work showed tumor markers to be within normal limits.

Clinical course and outcome

Surgical exploration was performed via an inguinal incision, and the spermatic cord was controlled with a penrose drain prior to delivering the left testis and paratesticular mass. The mass was noted to be completely distinct from the left testis and was able to be excised in its entirety with preservation of the left testis and no compromise to its vascular supply. Frozen analysis of the mass showed adipose tissue with myxoid changes and final pathology revealed a 2 cm well-encapsulated mass composed of adipocytes consistent with lipoblastoma with negative margins. The patient has since recovered uneventfully from surgery.

Discussion 

Adipose tumors are relatively rare in pediatric patients, accounting for approximately 6% of soft tissue neoplasms, with the majority of these being lipomas and up to 30% lipoblastomas.^1,2 Lipoblastomas occurring within the scrotum are even more unusual with fewer than 20 prior cases reported in the English literature.^2-5 Reflecting the epidemiology of lipoblastomas in general, the majority of these cases were reported in children less than three years old with the youngest reported case in a four month old (Kamel et al.) and only one case reported in an adult who was 37 years old (Pereira- Lourenço et al).^2,4,6 

Like lipomas, lipoblastomas are typically superficial and well-circumscribed; however, unlike lipomas, they tend to become less mobile as they enlarge and can be locally invasive despite their benign nature.¹ These tumors can grow quite large with the largest scrotal case reported being a 14 cm mass in a one-year-old male that grew in size over a five-month period.⁷ Histologically they are composed of sheets of adipocytes arranged in lobules separated by fibrovascular septa.¹ Treatment of lipoblastomas consists of surgical resection of the entire tumor and the prognosis is excellent with no reports of metastasis or malignant transformation. However, there is a risk of recurrence up to 46%, particularly with incomplete resection; for this reason long-term clinical follow up is recommended.¹ Recurrence has been reported to be more common with lipoblastomatosis, which is the diffuse type of lipoblastoma and demonstrates an infiltrative border on pathology making it more difficulty to completely excise.¹ The only reported case of recurrence in a scrotal lipoblastoma was by Somers et al. who reported a case of a 14 cm mass that was excised via an inguinal approach in a one year old and subsequently recurred six months later with two smaller lesions.⁷

Similar to our experience, most cases presented as enlarging, painless scrotal masses and because of the rarity of lipoblastomas the diagnosis was not suspected pre-operatively. The majority of cases were approached via an inguinal incision given the concern for potential malignancy and only two groups have reported using a scrotal approach.^2,4 As with our case, most authors have reported that the mass was distinct from the testis or very easy to separate from it allowing preservation of the testis once the diagnosis was confirmed to be benign on frozen pathology sections. However, two groups reported cases in which radical orchiectomy was performed in a 10- and 14-month-old patient given concern for malignancy, specifically paratesticular rhabdomyosarcoma.^3,8

Ideally, the diagnosis of testicular lipoblastoma could be made pre-operatively, decreasing parental and patient anxiety regarding potential malignancy and allowing testis preservation. Yada et al. suspected the diagnosis of scrotal lipoblastoma pre-operatively in a 19-month-old male based on scrotal ultrasound that showed a bi-lobed well-circumcised mass that was clearly outside the tunica vaginalis of the testis on imaging. Unlike our case, ultrasound revealed their patient’s mass to be hypovascular and they also obtained additional imaging with CT and MRI, which increased their confidence in the diagnosis and enabled a scrotal approach. Similarly, Pereira- Lourenço et al. reported a case in a 37-year-old male and pre-operative MRI showed the mass to be separate from the testis and compatible with lipoma and approached the lesion scrotally.⁴ Rousslang et al. suggested that both MRI and contrast enhanced ultrasound may be useful in making the diagnosis pre-operatively. The use of MRI has been reported to be helpful; however, in pediatric patients MRI typically requires anesthesia, decreasing its appeal. At this point, no group has specially reported their findings with contrast enhanced ultrasound of a scrotal lipoblastoma though this may be a useful adjunctive imaging study in these cases. 

Conclusion

Lipoblastoma is a very uncommon but benign cause of paratesticular scrotal mass in pediatric patients with less than twenty cases previously reported.  Though pre-operative diagnosis is difficult because of the rarity of this tumor and lack of distinguishing features on scrotal ultrasound, intra-operative diagnosis with frozen pathology sections can allow for a testis sparing resection in most cases. This is an important diagnosis for pediatric urologists to be familiar with so that they can recognize it when encountered on pathology and manage it appropriately.

Key points 

• Paratesticular lipoblastoma is a rare, benign cause of scrotal mass in young children
• Presented as a painless, enlarging paratesticular mass in an 18-month-old male
• Imaging raised concern for malignancy due to interval growth and vascularity
• Inguinal exploration with frozen section enabled testis-sparing excision
• Complete surgical resection is curative, though long-term surveillance is recommended due to recurrence risk

References

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