Hepatic angiomyolipoma (HAML) is an uncommon liver tumor characterized by having vascular, smooth muscle, and mature fat components [1]. Most cases of HAML are detected incidentally; however, initial presentation may include intratumoral hemorrhage and intraperitoneal hemorrhage, leading to acute abdominal pain. HAMLs are predominantly found in adult females residing in Asian countries like China and Japan [1]. Angiomyolipoma typically occurs in the kidneys, but the liver ranks as the second most common site. In addition to the histological presentation of adipose tissue, smooth muscle bundles, and thick-walled blood vessels, HAML characteristically presents with epithelioid cells [2]. HAML is most found in the right hepatic lobe as single or multiple, round or lobulated fat-containing lesions [1].

While the precise prevalence of HAML remains uncertain, it is estimated to range 300 to 600 cases globally, particularly affecting 5%−15% of patients diagnosed with tuberous sclerosis, an autosomal inherited phacomatosis associated with mental retardation, epilepsy, and adenoma sebaceum [3]. However, while HAMLs are typically benign, these tumors have a cumulative incidence of 4.1% for malignant behavior, exhibiting malignant characteristics, such as invasive growth, metastasis, and recurrence after resection. Therefore, the potential for malignant transformation underscores the significance of vigilant monitoring, as well as timely intervention within the framework of surgical management.

Due to its variable composition of adipose tissue, smooth muscle bundles, and thick-walled blood vessels, HAML may appear differently in different cases [4]. Under ultrasound (US), HAML can present as either a heterogeneous or homogeneous echogenic mass lesion [1]. On US alone, it may not be possible to distinguish the lesion from hemangiomas [5]. Color Doppler sonography will reveal a punctiform or filiform vascular distribution pattern. The most common diagnostic tool is computed tomography (CT), revealing a well-defined heterogeneous mass with a notably hypodense area. Magnetic resonance imaging (MRI) is the most specific imaging, but detection depends on the composition of adipose tissue. MRI shows either hyperintensity or hypointensity on T1-weighted images, and hyperintensity on T2-weighted images. Moreover, HAML typically drains through the hepatic vein, and can be distinguished from fat-containing hepatocellular carcinomas, which drain via portal veins, by identifying and characterizing a perfusing vein between the tumor center and hepatic vein [1,5].

For asymptomatic cases, observation is preferred over treatment, or conservative management involving close follow-up with histologically proven HAML smaller than 5 cm [1,3]. However, HAML-related mortality is low, with a risk estimate of 0.8% in surgically treated patients [3]. In cases of severe abdominal pain or intraperitoneal bleeding, preferred treatment options include embolization or surgical resection. Other potential surgical indications include aggressive patterns, such as vascular invasion, p53 immunoreactivity, or the rapid proliferation of tumor cells. Since most HAML follows benign clinical courses, observation is the most frequent method of treatment [6]. Tumor biopsy is usually avoided, due to the possibility of malignant tumor cells being disseminated into the peritoneal cavity. In cases where tumor malignancy cannot be ruled out using various imaging modalities, surgical resection may be suggested, in which surgical resection can be performed as open or laparoscopic, per oncological criteria [3,7].

However, robotic-assisted surgery offers a promising alternative by utilizing advanced robotic assistance to offer a tailored approach to managing HAML treatment. Through the use of such technology, this study portrays how HAMLs can be resected by navigating the intricate anatomy of the liver with greater dexterity and precision, facilitating improved tumor localization and excision, while reducing intraoperative blood loss, and minimizing the need for extensive tissue manipulation. As such, this case shows one of the first documented reports of a HAML resected via robot-assisted bisegmentectomy and cholecystectomy.

Prior written consent was gathered from the individual for the potential publication of identifiable images or data within this article. The study was approved under the blanket Tissue and Data Acquisition and Analysis Core (TDAAC) approval by Virginia Commonwealth University. The patient also granted written consent before the drafting of this article. Our patient is a previously healthy 57-year-old female who presented to the Hume–Lee transplant clinic for evaluation of bloating and elective right liver resection with cholecystectomy. Labs on admission showed lower hemoglobin of 9.3 g/dL (normal range: 12–16 g/dL) and hematocrit of 28.3% (normal range: 36%–44%). Alanine aminotransferase of 208 U/L (normal range: 7−56 U/L) and aspartate aminotransferase of 63 U/L (normal range: 10−36 U/L) were elevated.

Initial MRI showed a large 14.9 cm × 11.4 cm × 13.8 cm exophytic mass arriving from the inferior right hepatic lobe that was consistent with suspected hemangioma, with mass effect on the adjacent inferior vena cava, gallbladder, hepatic flexure, and anterior aspect of the right kidney. The inferior right hepatic lobe additionally showed a 0.7 cm T2 hyperintense non-enhancing focus (Fig. 1). Furthermore, the gallbladder was found to be under-distended with cholelithiasis. Intraoperative US was utilized to delineate the perimeter of the tumor and mark the planned transection line, taking note of the hepatic veins and Glisson’s structures in proximity.

Fig 1. (A) Axial view of (B) coronal view of magnetic resonance imaging showing large 14.9 cm exophytic mass arising from the inferior right hepatic lobe with non-enhancing hyperintensity.

Robotic bisegmentectomy of segments 5 and 6, along with the right inferior hepatic tumor, was completed on day one of patient admission. Postoperatively, hemoglobin levels increased, and stabilized with normal liver enzymes. The patient was admitted to surgical trauma intensive care unit postoperatively for hemodynamic monitoring and ventilator management in the setting of hypoxia and febrile illness, in which she was initiated with intravenous Zosyn for two days. The patient was discharged on postoperative day six with oral docusate, ondansetron, and oxycodone, and scheduled for follow-up with transplant surgery.

A tumor board was assembled to deliberate the patient’s case, in which surgical intervention was recommended based on the size of the liver tumor and her symptoms. The patient was briefed on the plan for a robotic right inferior bisegmentectomy with cholecystectomy, and the potential for open conversion, if needed. After deliberation, the patient agreed to move forward with the procedure. The surgery was performed on day one after she presented to care. The robotic surgery was performed using the Da Vinci Xi surgical system. Evaluation with the use of a camera through a port revealed the large right inferior hepatic tumor extending off of the right inferior liver, from segments 5 and 6, as anticipated from preoperative MRI with no other tumors. The cystic triangle of the gallbladder was dissected, and a critical view identifying the cystic duct and artery was obtained, in which both were clipped proximally and distally, and ligated. The gallbladder was then taken off its hepatic bed through electrocauterization. The parenchymal transection was achieved with the Pringle Maneuver, in which a catheter tube was fashioned around the porta hepatis, and then completed using robotic scissors, vessel sealer, and hemolock clips at crossing vessels. To facilitate division, a hanging maneuver was performed via placing a red rubber around the liver at the transection line, and vascular load endo-staplers were employed across the segment 5 and 6 Glisson’s sheaths. With parenchymal transection completed, hemostasis was subsequently achieved with cautery, Tachosil, Fibrillar, and Vistaseal fibrin sealant. The specimens, including the two segments with liver tumor and the gallbladder, were handed off to pathology, and tumor samples returned positive for HAML. Fig. 2 demonstrates critical portions of the robotic right inferior bisegmentectomy.

Fig 2. (A) Achieving access to the right inferior hepatic tumor off of segments 5 and 6. (B) Robot-assisted intraoperative ultrasound of tumor for the delineation of tumor perimeter. (C, D) Sealing the parenchymal transection with robotic scissors.

The surgical pathology revealed a 14 cm × 12.3 cm × 9.5 cm heterogeneous, mottled tan–yellow tumor, with areas of hemorrhage and degeneration. The background liver was grossly unremarkable. On microscopic examination, the tumor consisted of three components: adipose tissue, blood vessels, and spindled myoid cells. Immunohistochemistry demonstrated positive staining for MelanA and human melanoma black-45 antigen (HMB-45), supporting the diagnosis of HAML (Fig. 3).

Fig 3. (A) Juxtaposition of the myoid and vascular components of the tumor on the left with the normal liver on the right (H&E, ×20). (B) Intermixed epithelioid to spindled myoid cells and adipocytes (H&E, ×40). The myoid cells are positive for human melanoma black-45 antigen ×40 (C) and MelanA ×40 (D).

Initial and subsequent postoperative labs showed gradual normalizing liver function tests and stabilizing hemoglobin by day four. The patient’s recovery proceeded without complication, and she was discharged on day six with diet resumption and Oxycodone to control mild abdominal pain. At the two-week follow-up, no complications were noted on the outpatient follow-up. Labs at the three-month follow-up showed normal alanine aminotransferase of 33 U/L (normal range: 7−56 U/L) and aspartate aminotransferase of 33 U/L (normal range: 10−36 U/L), with normal total bilirubin of 0.5 (normal range: 0.1–1.2 mg/dL) and international normalized ratio of 1.0 (normal range: 0−1.1). CT abdomen/pelvis at five months postoperative showed an interval decrease in size of the postoperative fluid collection along the margin of the stable sub-centimeter right inferior lobe, demonstrated in Fig. 4.

Fig 4. Computed tomography scan with contrast image showing decrease in postoperative fluid collection along the inferior margin of the right hepatic lobe, 5-months postoperatively.

Angiomyolipomas primarily manifest in the kidney, with over 50% of cases associated with tuberous sclerosis complex (TSC) [4]. While HAMLs are considered rare, the liver represents the second most common site of involvement, with approximately 600 reported cases within the literature, while consisting of 0.4% of all primary liver tumors, and TSC being associated with approximately 10% of HAML patients [4,5,7]. HAMLs typically occur in non-cirrhotic livers, and mainly affect middle-aged women with a median age ranging 24−53 years [8]. The lesions tend to present as a solitary mass with distinct boundaries, but without encapsulation [8]. Patients diagnosed with HAML are primarily asymptomatic, but revealing symptoms may include abdominal discomfort, bloating, weight loss, or occasionally, the presence of an abdominal mass on palpation. As the tumor grows larger, patients may develop symptoms because of tumor compression, with a few severe cases revealing tumor rupture and hemorrhage [9]. Based on the tissue components and dominant tissue type, HAML can be classified into four categories: 1) hybrid, the most common type, characterized by a tumor containing nearly equal proportions of each tissue component; 2) myomas, primarily composed of smooth muscle cells; 3) lipomas, predominantly consisting of adipose tissue; and 4) hemangiomas, primarily composed of vascular tissue [10].

It is possible to misdiagnose HAML as other entities, both benign and malignant, including lipomas, hepatocellular adenomas and carcinomas, sarcoma, or other metastatic neoplasms [5]. Correct preoperative diagnosis has been difficult; but recently, several imaging methods have become available to diagnose HAML. Blood vessel and fat demonstrations represent crucial radiographic features [8]. However, due to the lesion’s rarity, such findings can be deemed as non-specific, due to inconsistent, variable fatty tissue proportions, resulting in various appearances [8,11]. Therefore, HAMLs must be further differentiated from other lesions of the liver that also contain fat, including malignant lesions, such as teratomas, hepatocellular carcinomas, liposarcomas, and hypervascular metastases [8,11]. US images are also highly variable, based on the composition of the lesion [6]. However, the typical appearance of HAML in US imaging was found to be a regular round or oval mass with clear boundaries [11]. Relying solely on US for different diagnoses may also be challenging when the tumor is predominantly composed of lipomatous tissue [6]. Contrast-enhanced US has shown significantly improved diagnostic ability. Plain CTs show heterogenous or homogenous low-density lesions, while contrast enhanced dynamic CTs show highly enhanced lesions during the arterial phase, prolonged enhancement during the portal phase, and potentially defective lesions in the late venous phase. Abdominal angiograms show tumor staining in both the arterial and portal phases. At present, MRIs are one of the best methods to determine tumor composition, revealing hyperintensity in T1 and T2 images, notably for lipomatous lesions.

A review by Yang et al. [12] of 92 patient cases diagnosed with HAML demonstrates the standard diagnostic procedure. A total of 92 patients with HAML were identified through retrospective analysis, and relevant clinical information was retrieved from the electronic medical records stored in pathology archive systems. Each patient underwent at least one imaging examination, which included US, CT, or MRI. In 91.3% of cases, HAML was typically a solitary tumor, while 8.7% (8 patients) of cases had two or more tumors. Only 15.2% of cases could be initially diagnosed, as the remaining cases either presented with atypical symptoms or lacked clinical findings, necessitating reliance on primitive imaging tools for the initial diagnosis. In plain CT imaging, 5 lesions exhibited high density, whereas 50 lesions displayed high density, 11 of these being heterogeneously dense. High signal intensity in the arterial phase was observed in T1-weighted images of MRIs in 13 cases, while only 4 cases showed low signal intensity. Similar to our patient’s MRI, high signal intensity was found in T2-weighted images of 15 cases, and 30 patients underwent intraoperative US to improve radical resection rates and avoid damage to important liver structures. Due to the difficulty of preoperative diagnosis, the final diagnosis for all cases was confirmed by guided biopsy.

Furthermore, a patient case report by Günster et al. [3] detailing symptomatic HAML revealed MRI findings of a mass within left liver segments II and III with inhomogeneous intensity in T1- and T2-weighted sequences, accompanied by cystic and hemorrhagic composition, marginal hyperperfusion, diffusion restriction, and areas with large proportions of fat. With imaging generally inconclusive, histology completed via fine needle biopsy showed mesenchymal neoplasia characterized by the presence of lipomatous tissue and smooth muscle cells, alongside evidence of extramedullary hematopoiesis and notable positivity for HMB-45. The presence of the suspected symptomatic HAML and indicated displacing growth warranted surgical resection. A left lobectomy was subsequently conducted to remove the cystic tumor from segments II and III, along with clear visualization of the anterior stomach wall. Intraoperative US of the liver defined the limits for resection, and confirmed the lack of infiltrative growth. The pathological evaluation of excised tissue confirmed the diagnosis of HAML. Measuring 16 cm × 15 cm × 6.5 cm, the resected tumor was lipomatous with adipocytes and myogenic, displaying spindle and epithelioid cell morphology. Subsequent immunohistochemical analysis of the resected tissue revealed strong positivity for HMB-45.

However, our case report marks the documentation of robotic-assisted surgical resection of a right inferior lobe HAML, showcasing the innovative application of robotic surgical techniques in the treatment of this rare liver lesion. Using robot assistance in surgery represents an evolution of traditional minimally invasive surgical techniques [13]. That most laparoscopic procedures can be performed through robotic assistance underlines a transition from open surgery to laparoscopic surgery, and further, to robot-assisted surgery [14]. Several factors related to the laparoscopic approach pose significant limitations for conducting complex hepatectomies, especially for larger tumors, including the use of unstable cameras, instruments with limited degrees of freedom and rigidity, human hand tremors, ergonomic challenges, and the difficulty of suturing in hard-to-reach locations [15]. Robotic systems have compensated for the limitations inherent in laparoscopic approaches by using stable, 3D high-definition cameras that can eliminate hand tremors [15]. The primary advantage of robotic surgery lies in its ability to offer seven degrees of freedom, which can help overcome the difficulties arising from rigid laparoscopic instruments by increasing manual dexterity and enabling smoother instrument movements, while better facilitating liver resections via precise instrumental control during repetitive motions and operations within deep cavities [14-16]. During the resections of huge liver tumors, robotic instruments can aid in the precise dissection of the individual hepatic artery and portal vein, especially in cases of distorted anatomy [16]. They also improve the dissection and control of short hepatic veins within the hepatocaval region, while simplifying the process of suturing bleeders during parenchymal transection [15,16]. Furthermore, it has been shown that robotic platforms can also reduce musculoskeletal strain and physical workload for surgeons, while improving posture during longer procedures, potentially reducing technical error as a result of human fatigue [15-17]. During robotic-assisted liver resections, intraoperative open procedure conversion is also known to be less frequent, compared to laparoscopic liver resections [18]. In addition, cost analysis from prior studies have shown a lower total cost for robotic liver surgeries as a result of further shortening of hospital stays and absences of severe complications, as well as the lower costs of instruments and accessories, compared to laparoscopic surgeries [19].

This report signifies a significant advancement in surgical approaches, and highlights the potential for enhanced precision and minimally invasive interventions in the future management of HAMLs. The decision for the robotic approach was motivated by its capacity for exceptional visualization and control during minimally invasive surgeries. The robotic platform further facilitates precise dissections, and ensures effective hemostasis. Other existing field reports emphasize the strategic benefits of employing surgical robots, particularly in resections of greater complexity, highlighting further growth in minimally invasive surgical resections [14,15].

To delve deeper into the clinical characteristics and outcomes of HAML, we conducted a thorough examination of case reports concerning both symptomatic and asymptomatic HAML. Table 1 presents details on the primary diagnosis and indication, surgical approach, and documented complications.

Table 1 . Literature review of previously observed cases of hepatic angiomyolipoma, including the number of cases, presenting symptoms, surgical treatment option, and complications, if any

Author	Year	Study design	Patient	Patients with HAML	Primary diagnosis/indication	Operative technique	Complication
Zhu et al. [10]	2022	Case series	12	12	Epigastric pain (3), incidental (9)	Left lateral segmentectomy (4), partial hepatectomy (6), extended left hemihepatectomy (2)	Bilateral pleural effusion (1), moderate fever (1)
Günster et al. [3]	2020	Case report	1	1	Abdominal discomfort, feeling of fullness	Left lobe lobectomy
Klompenhouwer et al. [4]	2020	Retrospective cohort	38	38	Abdominal pain or distension (19), asymptomatic (16), acute liver bleeding (1)	Surgical resection (29), observation (4), liver transplant (3), lost-to-follow-up (2)	Recurrence (2)
Yang et al. [12]	2018	Retrospective cohort	92	92	Upper abdominal pain (14), abdominal distention (2), backache (2), abdominal discomfort (2), shoulder pain (2), weight loss (1)	Partial hepatectomy (68), US-guided radiofrequency ablation (22), liver biopsy (2)	Recurrence (2)
Damaskos et al. [2]	2017	Case report	1	1	Right upper quadrant abdominal pain	Laparoscopic left lateral hepatectomy and concurrent cholecystectomy
Ortiz and Tortosa [8]	2016	Retrospective cohort	4	4	Abdominal pain (1), non-specific (1), incidental (2)	Core needle biopsy (3), surgery (1)
Theodosopoulos et al. [11]	2013	Retrospective cohort	56	5	Abdominal discomfort (1), palpable mass (1), asymptomatic (3)	Segmentectomies and atypical liver resections (5)	Respiratory infection (1), biloma (1), urinary tract infection (1)
Butte et al. [7]	2011	Retrospective cohort	238	22	HAML (15), abdominal pain (7)	Resection (13), embolization (3), systemic chemotherapy (2), observation (4)	Recurrence (13)
Ding et al. [9]	2011	Retrospective cohort	79	79	Right upper abdominal discomfort (20), general malaise (5), incidental (54)	Liver resection (79)	Recurrence (1), non-specific complaints (8)

None of the observed cases were treated using a robotic technique.

Values are presented as number only.

HAML, hepatic angiomyolipoma; US, ultrasound.

In conclusion, this case report details a 57-year-old female with a right inferior HAML of liver segments 5 and 6. The patient exhibited symptoms of bloating, with concerns of a liver lesion. MRI studies revealed a large exophytic mass and T2 hyperintense lesion off of the inferior right hepatic lobe, which was consistent with HAML. The patient underwent a robotic right inferior bisegmentectomy with cholecystectomy. US-guided robot-assisted biopsy and surgical pathology with microscopic examination confirmed the post-operative diagnosis of HAML. The patient successfully recovered after surgery, and has undergone outpatient follow-up with no complications.

HAML is a rare, noncancerous liver tumor of mesenchymal origin that mimics hepatic malignancy in presentation, and should consistently be considered within the differential diagnosis of patients with single or multiple hepatic lesions. However, HAML remains challenging to diagnose, but advances in imaging techniques, which include a combination of US, CT, MRI, and angiography, have led to more precise diagnosis of HAML. Pathologic examination continues to be a crucial step in reaching a final diagnosis, especially with the utilization of HMB-45 staining.

In this patient’s case, a robotic-assisted bisegmentectomy with cholecystectomy was employed as the surgical approach. Robotic assistance was chosen due to its ability to enable minimally invasive surgery with enhanced surgical precision, dexterity, and three-dimensional imaging. Subsequently, the robotic system facilitated precise dissection of the gallbladder, transection of liver parenchyma, and effective hemostasis.

None.

No potential conflict of interest relevant to this article was reported.

Conceptualization: SL. Data curation: AP, KS, AA, SL. Methodology: All authors. Writing - original draft: All authors. Writing - review & editing: All authors.