Angiomyolipomatous lesions in the nasal cavity such AML and AL, which are composed of smooth muscle and vasculature with and without adipocytes, have been sparsely characterized in the literature. AL is described as a subtype of leiomyoma within the WHO Head and Neck smooth muscle tumor category. It is exceedingly rare in the nasal cavity. It is unknown whether nasal AL harbors similar or divergent molecular alterations to AML. Alterations associated with the PEComatous renal and hepatic AML include biallelic loss of the tumor suppressor genes, TSC1 or TSC2, or, alternatively, TFE3 gene fusions [24]. Genes or pathways reported as implicated in AL include monosomy of chromosome 13; loss of 6p, 13q, 21q, and 22q; recurrent gain at Xq; and rarely, NOTCH2 gene arrangement [25–31]. The MED12 and HMGA2 rearrangements of genital and retroperitoneal leiomyomas have not been reported in sinonasal leiomyomas [32–33]. Due to the rarity of these nasal cavity lesions, the literature and experience are largely limited to case reports. To our knowledge, our research is first to evaluate the genetic landscape of angiomyolipomatous lesions of the nasal cavity through SNP array, whole exome sequencing, and RNA sequencing.
In our case series of 15 nasal cavity angiomyolipomatous lesions (11 AML and four AL, mean size 22 mm), there was a striking 87% male patient predominance with no clinical history of TSC. Radiographic studies revealed variable features of bony erosion, osseous remodeling, and mucosal thickening. Most tumors demonstrated a circumscribed growth pattern. Surface ulceration and associated surface necrosis, vascular thrombosis, chronic inflammation, myxoid change, and vascular changes were seen in a subset of cases. Well-developed epithelioid cell morphology or melanocytic immunophenotypic signatures were not identified. Despite typically positive surgical margins, we observed no case recurrences during the study follow-up period, and only one case (patient #12) clinically represented recurrent disease. In summary, we confirmed that AML in the nasal cavity, compared to the more common kidney or liver locations, lacks epithelioid morphology, melanocytic immunoexpression, and association with TSC; it is indeed thereby best considered as a non-PEComatous entity [18–19]. We also suggest that nasal “AML” and “AL” are likely the same entity, given the significant histologic overlap and immunophenotypic profile and no clinically relevant, distinguishing genetic features.
Molecular analysis revealed loss of 3p and 11q in a single AML (patient #5, Fig. 4). Interestingly, this was the eldest patient at 75 years (study mean age, 60 years) and was one of only two patients that exhibited bony erosion on radiographic imaging, though the size of his AML and clinical history are unknown. The clinical significance of the 3p and 11q loss is unclear, as findings have not otherwise been reported in angiomyolipomatous lesions. However, in more than 90% of sporadic clear cell renal cell carcinomas, loss of chromosome 3p, which harbors tumor suppressors VHL on 3p25 and PBRM1, BAP1, and SETD2 on 3p21, is an established occurrence [34]. Deletion of chromosome 11q is implicated in neuroblastoma, conferring poorer prognosis in high-risk patients [35]. Deletion of 3p is also shown to be nonrandomly associated with deletion of 11q in neuroblastoma [36]. Overall, no other known pathogenic CNV, LOH regions, or classic molecular alterations were seen, including in TSC1/2, TFE3, and NOTCH2. One variant of uncertain significance (VUS) involving TSC2 was identified (patient #15). This TSC2 variant is a splice site donor (with one report in ClinVar [Variation ID: 2683333]). Similar splice variants in this region are considered benign. Several other VUS were also identified (Table 2), two of which were seen in genes associated with the androgen receptor (NCOR1 and MDC1) [37–38]. While these variants are insufficiently characterized in existing literature and genomic databases to ascertain their potential biologic significance, in the context of the predominant male predilection noted clinically, the possibility of a hormonal response component in the pathogenesis of these lesions is raised. This response may be possibly analogous to sinonasal tract angiofibroma, a lesion that exclusively affects male patients and demonstrates a hormone dependent growth pattern correlated with puberty onset and strong androgen receptor expression [39–41].
Entities such as AML and AL pose a diagnostic challenge with regard to developing consistent nomenclature and defining them as either neoplastic or hamartomatous. Derived from the Greek root hamartia (“to miss the mark”), hamartomas consist of an abnormal proliferation of cells normally found in an anatomic region but failing to form the structures expected for the region [42]. Some authors also indicate that hamartomas should show evidence of being present near the time of birth [43]. Hamartomas may also show clonality, which blurs the distinction from true neoplasms. The WHO Head and Neck tumor categories of nasal hamartomas currently includes only respiratory epithelial adenomatoid hamartoma (REAH), seromucinous hamartoma (SH), and nasal chondromesenchymal hamartoma (NCMH) [44]. The unusually high fractional allelic loss of 31% for REAH suggests it may be a benign neoplasm [45], though recent evidence show its lack of KRAS, BRAF, or EGFR mutations [46]. There have been documented EGFR::ZNF267 gene fusions [45] and increased mutation rates in heteroplasmy [47] in SH, suggesting it as a benign neoplasm. Thirdly, NCMH has been shown to exhibit somatic DICER1 missense mutations [48] as well as a t(12;17)(q24.1;q21) translocation [49], classifying it as a benign neoplasm of nasopharynx, though the terminology of hamartoma is retained. Therefore, each of the three WHO-classified hamartomas of the nasal cavity exhibit unique genetic aberrations. However, in contrast to neoplasms, hamartomas typically have self-limited growth and do not recur [50]. For example, in a retrospective study of sinonasal REAH, 49 cases were endoscopically resected without recurrence in a mean follow-up period of 27.2 months [51]. In this delicate anatomic location, where even small lesions present with symptoms (nasal obstruction), surgical excision may be favored clinically over observation (unlike renal or liver AMLs). Resections of hamartomas appear to be curative [51]. Similarly, in the largest series of sinonasal angioleiomyomas, no recurrences occurred after local excision [5].
The classification of nasal tumors with features of non-PEComatous AML has been inconsistent and controversial in the literature. Diagnostic proposals have included: “angiomyolipomatous hamartoma”, wherein authors favored these termed lesions as non-PEComatous and likely non-neoplastic, though molecular testing was not performed [9]; “mucocutaneous AML” [12], “nasal AML”, and “sinonasal AL with adipocytic differentiation” [3]. In a series of 16 sinonasal ALs, authors noted that 25% demonstrated mature adipocytes and in reviewing the literature noted adipocytes in a higher proportion (35%) of sinonasal ALs compared to the cutaneous counterparts (2.8%) [5]. Furthermore, AL with adipocytic differentiation tended to affect males more (63%) compared to AL without adipocytic differentiation (46%) [5]. In our multi-institutional study with multiple participating pathologists, we noted variability in the diagnostic nomenclature used in practice for these lesions. Five cases, initially submitted as “sinonasal AL with adipocytic differentiation” and “AL (vascular leiomyoma)”, were re-classified to AML once defining lesions with any amount of adipose tissue as AML for the purposes of this study. However, we do note the controversy of simply labeling these nasal cavity lesions as “AML”, as cautioned by Tosios, et al. [52]: AML is a well-studied and defined entity to clinicians, conferring specific diagnostic value to clinicians and patients that may otherwise mislead.
In conclusion, angiomyolipomatous lesions in the nasal cavity warrant a universally adopted nomenclature. Genetic analysis shows that sinonasal angiomyolipomatous lesions distinct from neoplastic, PEComatous angiomyolipomatous lesions of the kidney, lacking alterations in the known PEComa-related genes. Therefore, while these benign nasal cavity lesions could reasonably descriptively be termed as “angiomyolipomatous hamartomas” [9], this nomenclature may be misleading because of its tendency to invoke associations with PEComatous AML. Most of these lesions affect adults without evidence of origin near the time of birth, calling into question characterization as hamartomatous. Thus, it may be most prudent to endorse the nomenclature of “sinonasal angioleiomyoma with adipocytic differentiation.”