Endolymphatic sac tumor showing increased activity on 68Ga-DOTA-TATE PET/CT

Abstract

Endolymphatic sac tumors (ELSTs) are rare tumors arising from the epithelium of the endolymphatic sac and duct that can be either sporadic or associated with von Hippel-Lindau (VHL) disease. We report a case of a VHL patient with histologically proven residual ELST, who underwent ⁶⁸Ga-DOTA-TATE-PET/CT showing increased activity (SUVmax: 6.29) by the ELST. The presented case of a VHL-associated ELST with increased ⁶⁸Ga-DOTA-TATE uptake indicates cell-surface expression of somatostatin receptors (SSTR) by this tumor, suggesting the potential application of SSTR-imaging using ⁶⁸Ga-DOTA-conjugated-peptides in the work-up and management of these patients.

A 46-year-old gentleman with known history of von Hippel-Lindau (VHL) disease and partial resection of right-sided temporal bone mass histologically proven to be endolymphatic sac tumor (ELST) was followed up over a period of 14 years. Surveillance imaging with consecutive magnetic resonance (MR) scans showed stable residual ELST localized within the right temporal bone causing destruction of all right inner-ear structures (post-contrast T1-weighted image - white arrows; Fig. A), markedly enhancing on post-contrast fluid-attenuated inversion recovery (FLAIR) images (Fig. B, yellow arrows). In addition to anatomical imaging the patient was evaluated with whole body PET/CT using ⁶⁸Ga-DOTA-TATE for the detection of neuroendocrine lesions, showing increased activity (SUVmax:6.29) by the residual ELST (Fig. C, white arrows). ELSTs are rare, slow-growing, locally aggressive, low-grade papillary malignancies originating from the epithelium of the endolymphatic duct and sac [1]. Depending on tumor extension, ELSTs present with cochleovestibular dysfunction, sensorineural hearing loss, tinnitus, vertigo, ataxia, disequilibrium or even facial weakness and glossopharyngeal nerve deficits [2]. Although ELSTs do not give distant hematogenous metastasis, “drop metastasis” to the spinal canal may occur, while death can happen secondary to intracranial vascular compromise [3, 4]. ELSTs can be either sporadic or associated with VHL disease, a familial cancer syndrome characterized by the development of a wide spectrum of benign and malignant tumors [5]. VHL-associated ELSTs appear to occur at younger ages, with predilection for women and are more frequently bilateral [6]. Microscopic abnormalities in the epithelium of the endolymphatic sac and duct similar to those of ELSTs are found in VHL patients even though they do not present clinical or radiological manifestations of the tumor [7]. Since, multiple VHL manifestations such as hemangioblastomas or pancreatic neuroendocrine tumors (NETs) are known to over-express somatostatin receptors (SSTRs), SSTR imaging with radiolabeled SST-analogues has been employed in the work-up of this disease [8-10]. The conjunction of SST-analogues with the chelator DOTA-, enabled labelling with the PET-emitter ⁶⁸Ga-, providing compounds with higher affinity to SSTRs compared to those used for conventional SSTR-imaging with single photon emission computed tomography (SPECT). Moreover, the superior resolution provided by hybrid PET/CT makes SSTR imaging using ⁶⁸Ga-DOTA-conjugated-peptides the new standard of reference for the detection and characterization of SSTR-positive lesions [11, 12]. The presented case of a VHL-associated ELST showing increased activity on ⁶⁸Ga-DOTA-TATE PET/CT, suggests cell-surface over-expression of SSTRs and particularly SSTR-2 for which ⁶⁸Ga-DOTA-TATE has a predominant affinity. This observation sheds more light to the behavior of this rare tumor and indicates the potential application of PET/CT imaging with ⁶⁸Ga-DOTA-TATE in the early detection of ELST, which could enable less morbid operations with higher likelihood for cure and hearing preservation. Furthermore, monitoring of disease progression as well as theranostic application of peptide receptor radionuclide therapy (PRRT) in patients with residual or recurrent ELSTs are potential benefits of SSTR imaging using ⁶⁸Ga-DOTA-conjugated-peptides that need to be further investigated.