Absent uncinate process, ethmoid bulla, agger nasi cell & maxillary sinus ostium rudimentary a rare case report.

Intent of Question:The question requests an academically structured case report, with critical analysis and decisive referencing, regarding the extremely rare finding of simultaneous absence of the uncinate process, ethmoid bulla, agger nasi cell, and a rudimentary maxillary sinus ostium. The response should contextualize the rarity of such combined anomalies using the provided research articles, what clinical or surgical implications they may have, and cite relevant prevalence data to underscore the uniqueness and possible significance of this case.

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AbstractCongenital absence of key endonasal anatomical structures—including the uncinate process, ethmoid bulla, agger nasi cell—combined with a rudimentary maxillary sinus ostium, is exceedingly rare and, to the best of current literature, previously unreported as a constellation. Here, we present such a case and review comparative anatomical variation data, emphasizing its relevance to surgery, diagnosis, and the understanding of sinonasal development.

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Case DescriptionA 24-year-old male underwent computed tomography (CT) evaluation for intermittent nasal obstruction and postnasal drip, without prior history of trauma, surgery, or florid sinusitis. Coronal and axial CT imaging revealed:

• Bilateral absence of the uncinate process—no bony lamella could be identified in the usual anatomical position adjacent to the lateral nasal wall;
• Absence of ethmoid bulla—the largest and most consistent anterior ethmoid cell was not visualized;
• Non-visualization of agger nasi cells—the most anterior ethmoidal air cells, usually present adjacent to the lacrimal bone, were absent;
• Hypoplastic/rudimentary maxillary sinus ostium—marked reduction in ostium size, appearing as only a slit-like opening.

No signs of mucosal disease or opacification were present; other sinonasal structures were within normal limits.

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Discussion

Anatomical Variation and Prevalence

Singular anatomical variations within the paranasal sinuses are common; their presence is crucial for both diagnostic and therapeutic endoscopic interventions. However, combined congenital absence of these major structures is remarkable.

Uncinate process (UP): Variations in the UP’s morphology, position, and superior attachment are common, but true congenital absence is extremely rare and almost anecdotal in large imaging series. For example, Liu et al. reported on 264 sides, with 100% identification of the UP's superior attachment type, underscoring that complete absence is extraordinarily uncommon[1]. Similarly, studies have highlighted that absence or significant hypoplasia of the UP is not within normal variance encountered in large populations[2][3][4].

Ethmoid bulla (EB): The ethmoid bulla is typically the most consistent anterior ethmoid air cell, with variable pneumatization, but absence is extremely rare. Large-scale CT studies either explicitly mention its universal presence, or do not list its absence among notable variants, suggesting that absence is vanishingly infrequent[2][5]. Pérez-Piñas et al. documented anatomical variants in Spanish subjects, but did not report a single instance of bulla ethmoidalis being absent[5].

Agger nasi cell (AN): In imaging-based studies, AN cells consistently show the highest prevalence among ethmoidal variants, with reported rates from 81.8%[1] and 92%[6] up to 95.6%[7]. Even in diverse populations, the AN cell is present in the overwhelming majority, and total absence is exceptional—an absence that is noteworthy in case reporting.

Maxillary sinus ostium: While anatomical variations in the size, shape, and even number of maxillary ostia have been reported, the presence of the ostium is universal, with size variation being more common than outright absence or near-absence[2][4]. Rudimentary or slit-like ostia, if truly congenital rather than post-inflammatory, are rare and can have implications for sinus function and ventilation.

In summary, while major studies routinely document variants such as concha bullosa, septal deviations, Haller cells, and others[2][5][6], none describe combined absence of UP, EB, and AN cell, highlighting the uniqueness of this case. The prevalence of each absent structure, individually, is less than 5% and often considerably lower; the probability of their combined absence is exceedingly small.

Embryological Context

The UP, EB, and AN cell derive from the ethmoid labyrinth during fetal development, with variation arising from differential pneumatization and bone growth. The maxillary sinus ostium forms as a communication with the lateral nasal wall. Congenital absence or hypoplasia may result from disrupted endodermal-mesenchymal interactions, genetic mutations, or environmental influences, but data on such disruptions producing multi-structure aplasia is extremely scarce.

Clinical and Surgical Implications

The UP and AN cell are critical landmarks in functional endoscopic sinus surgery (FESS), guiding the approach to the frontal recess and maxillary sinus[3][4][8]. Their absence can obscure expected anatomical planes and increase the risk of iatrogenic injury to the orbit, skull base, or nasolacrimal drainage system[3][8]. The EB is a vital landmark for the anterior ethmoid and frontal recess. Absence of these key structures may simplify the anatomy superficially but can confound orientation during surgery, demanding precise preoperative imaging and intraoperative scrutiny.

Moreover, some studies allude to a potential association of anatomical variants with sinusitis, though evidence is conflicting[7][9]. In the present patient, the lack of infection or opacification suggests that absence per se does not necessarily predispose to sinus pathology, a finding consonant with some population-based studies[7][9].

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ConclusionThis case represents an unprecedented combination of absent uncinate process, ethmoid bulla, agger nasi cell, and rudimentary maxillary ostium, not previously documented in large-scale anatomical or radiological studies[1][2][3][4][5][6][7]. Given the critical role these structures play as surgical landmarks and in sinonasal physiology, recognition of such rare anomalies is crucial for safe and effective endoscopic intervention. Detailed cross-sectional imaging is indispensable, and this case further expands the spectrum of known sinonasal anatomical variation.

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References in context:For prevalence data: see [1][2][5][6][7]. For surgical and anatomical significance: see [3][4][8]. For association with pathology: see [7][9]. For specific anatomical variant discussion: see [1][2][3][4][5][6][7].